Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 832 insertions, 0 deletions

diff --git a/linux-user/mmap.c b/linux-user/mmap.c
new file mode 100644
index 000000000..c125031b9
--- /dev/null
+++ b/linux-user/mmap.c
@@ -0,0 +1,832 @@
+/*
+ *  mmap support for qemu
+ *
+ *  Copyright (c) 2003 Fabrice Bellard
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+#include "qemu/osdep.h"
+#include "trace.h"
+#include "exec/log.h"
+#include "qemu.h"
+#include "user-internals.h"
+#include "user-mmap.h"
+
+static pthread_mutex_t mmap_mutex = PTHREAD_MUTEX_INITIALIZER;
+static __thread int mmap_lock_count;
+
+void mmap_lock(void)
+{
+    if (mmap_lock_count++ == 0) {
+        pthread_mutex_lock(&mmap_mutex);
+    }
+}
+
+void mmap_unlock(void)
+{
+    if (--mmap_lock_count == 0) {
+        pthread_mutex_unlock(&mmap_mutex);
+    }
+}
+
+bool have_mmap_lock(void)
+{
+    return mmap_lock_count > 0 ? true : false;
+}
+
+/* Grab lock to make sure things are in a consistent state after fork().  */
+void mmap_fork_start(void)
+{
+    if (mmap_lock_count)
+        abort();
+    pthread_mutex_lock(&mmap_mutex);
+}
+
+void mmap_fork_end(int child)
+{
+    if (child)
+        pthread_mutex_init(&mmap_mutex, NULL);
+    else
+        pthread_mutex_unlock(&mmap_mutex);
+}
+
+/*
+ * Validate target prot bitmask.
+ * Return the prot bitmask for the host in *HOST_PROT.
+ * Return 0 if the target prot bitmask is invalid, otherwise
+ * the internal qemu page_flags (which will include PAGE_VALID).
+ */
+static int validate_prot_to_pageflags(int *host_prot, int prot)
+{
+    int valid = PROT_READ | PROT_WRITE | PROT_EXEC | TARGET_PROT_SEM;
+    int page_flags = (prot & PAGE_BITS) | PAGE_VALID;
+
+    /*
+     * For the host, we need not pass anything except read/write/exec.
+     * While PROT_SEM is allowed by all hosts, it is also ignored, so
+     * don't bother transforming guest bit to host bit.  Any other
+     * target-specific prot bits will not be understood by the host
+     * and will need to be encoded into page_flags for qemu emulation.
+     *
+     * Pages that are executable by the guest will never be executed
+     * by the host, but the host will need to be able to read them.
+     */
+    *host_prot = (prot & (PROT_READ | PROT_WRITE))
+               | (prot & PROT_EXEC ? PROT_READ : 0);
+
+#ifdef TARGET_AARCH64
+    {
+        ARMCPU *cpu = ARM_CPU(thread_cpu);
+
+        /*
+         * The PROT_BTI bit is only accepted if the cpu supports the feature.
+         * Since this is the unusual case, don't bother checking unless
+         * the bit has been requested.  If set and valid, record the bit
+         * within QEMU's page_flags.
+         */
+        if ((prot & TARGET_PROT_BTI) && cpu_isar_feature(aa64_bti, cpu)) {
+            valid |= TARGET_PROT_BTI;
+            page_flags |= PAGE_BTI;
+        }
+        /* Similarly for the PROT_MTE bit. */
+        if ((prot & TARGET_PROT_MTE) && cpu_isar_feature(aa64_mte, cpu)) {
+            valid |= TARGET_PROT_MTE;
+            page_flags |= PAGE_MTE;
+        }
+    }
+#endif
+
+    return prot & ~valid ? 0 : page_flags;
+}
+
+/* NOTE: all the constants are the HOST ones, but addresses are target. */
+int target_mprotect(abi_ulong start, abi_ulong len, int target_prot)
+{
+    abi_ulong end, host_start, host_end, addr;
+    int prot1, ret, page_flags, host_prot;
+
+    trace_target_mprotect(start, len, target_prot);
+
+    if ((start & ~TARGET_PAGE_MASK) != 0) {
+        return -TARGET_EINVAL;
+    }
+    page_flags = validate_prot_to_pageflags(&host_prot, target_prot);
+    if (!page_flags) {
+        return -TARGET_EINVAL;
+    }
+    len = TARGET_PAGE_ALIGN(len);
+    end = start + len;
+    if (!guest_range_valid_untagged(start, len)) {
+        return -TARGET_ENOMEM;
+    }
+    if (len == 0) {
+        return 0;
+    }
+
+    mmap_lock();
+    host_start = start & qemu_host_page_mask;
+    host_end = HOST_PAGE_ALIGN(end);
+    if (start > host_start) {
+        /* handle host page containing start */
+        prot1 = host_prot;
+        for (addr = host_start; addr < start; addr += TARGET_PAGE_SIZE) {
+            prot1 |= page_get_flags(addr);
+        }
+        if (host_end == host_start + qemu_host_page_size) {
+            for (addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
+                prot1 |= page_get_flags(addr);
+            }
+            end = host_end;
+        }
+        ret = mprotect(g2h_untagged(host_start), qemu_host_page_size,
+                       prot1 & PAGE_BITS);
+        if (ret != 0) {
+            goto error;
+        }
+        host_start += qemu_host_page_size;
+    }
+    if (end < host_end) {
+        prot1 = host_prot;
+        for (addr = end; addr < host_end; addr += TARGET_PAGE_SIZE) {
+            prot1 |= page_get_flags(addr);
+        }
+        ret = mprotect(g2h_untagged(host_end - qemu_host_page_size),
+                       qemu_host_page_size, prot1 & PAGE_BITS);
+        if (ret != 0) {
+            goto error;
+        }
+        host_end -= qemu_host_page_size;
+    }
+
+    /* handle the pages in the middle */
+    if (host_start < host_end) {
+        ret = mprotect(g2h_untagged(host_start),
+                       host_end - host_start, host_prot);
+        if (ret != 0) {
+            goto error;
+        }
+    }
+    page_set_flags(start, start + len, page_flags);
+    mmap_unlock();
+    return 0;
+error:
+    mmap_unlock();
+    return ret;
+}
+
+/* map an incomplete host page */
+static int mmap_frag(abi_ulong real_start,
+                     abi_ulong start, abi_ulong end,
+                     int prot, int flags, int fd, abi_ulong offset)
+{
+    abi_ulong real_end, addr;
+    void *host_start;
+    int prot1, prot_new;
+
+    real_end = real_start + qemu_host_page_size;
+    host_start = g2h_untagged(real_start);
+
+    /* get the protection of the target pages outside the mapping */
+    prot1 = 0;
+    for(addr = real_start; addr < real_end; addr++) {
+        if (addr < start || addr >= end)
+            prot1 |= page_get_flags(addr);
+    }
+
+    if (prot1 == 0) {
+        /* no page was there, so we allocate one */
+        void *p = mmap(host_start, qemu_host_page_size, prot,
+                       flags | MAP_ANONYMOUS, -1, 0);
+        if (p == MAP_FAILED)
+            return -1;
+        prot1 = prot;
+    }
+    prot1 &= PAGE_BITS;
+
+    prot_new = prot | prot1;
+    if (!(flags & MAP_ANONYMOUS)) {
+        /* msync() won't work here, so we return an error if write is
+           possible while it is a shared mapping */
+        if ((flags & MAP_TYPE) == MAP_SHARED &&
+            (prot & PROT_WRITE))
+            return -1;
+
+        /* adjust protection to be able to read */
+        if (!(prot1 & PROT_WRITE))
+            mprotect(host_start, qemu_host_page_size, prot1 | PROT_WRITE);
+
+        /* read the corresponding file data */
+        if (pread(fd, g2h_untagged(start), end - start, offset) == -1)
+            return -1;
+
+        /* put final protection */
+        if (prot_new != (prot1 | PROT_WRITE))
+            mprotect(host_start, qemu_host_page_size, prot_new);
+    } else {
+        if (prot_new != prot1) {
+            mprotect(host_start, qemu_host_page_size, prot_new);
+        }
+        if (prot_new & PROT_WRITE) {
+            memset(g2h_untagged(start), 0, end - start);
+        }
+    }
+    return 0;
+}
+
+#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
+#ifdef TARGET_AARCH64
+# define TASK_UNMAPPED_BASE  0x5500000000
+#else
+# define TASK_UNMAPPED_BASE  (1ul << 38)
+#endif
+#else
+# define TASK_UNMAPPED_BASE  0x40000000
+#endif
+abi_ulong mmap_next_start = TASK_UNMAPPED_BASE;
+
+unsigned long last_brk;
+
+/* Subroutine of mmap_find_vma, used when we have pre-allocated a chunk
+   of guest address space.  */
+static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size,
+                                        abi_ulong align)
+{
+    abi_ulong addr, end_addr, incr = qemu_host_page_size;
+    int prot;
+    bool looped = false;
+
+    if (size > reserved_va) {
+        return (abi_ulong)-1;
+    }
+
+    /* Note that start and size have already been aligned by mmap_find_vma. */
+
+    end_addr = start + size;
+    if (start > reserved_va - size) {
+        /* Start at the top of the address space.  */
+        end_addr = ((reserved_va - size) & -align) + size;
+        looped = true;
+    }
+
+    /* Search downward from END_ADDR, checking to see if a page is in use.  */
+    addr = end_addr;
+    while (1) {
+        addr -= incr;
+        if (addr > end_addr) {
+            if (looped) {
+                /* Failure.  The entire address space has been searched.  */
+                return (abi_ulong)-1;
+            }
+            /* Re-start at the top of the address space.  */
+            addr = end_addr = ((reserved_va - size) & -align) + size;
+            looped = true;
+        } else {
+            prot = page_get_flags(addr);
+            if (prot) {
+                /* Page in use.  Restart below this page.  */
+                addr = end_addr = ((addr - size) & -align) + size;
+            } else if (addr && addr + size == end_addr) {
+                /* Success!  All pages between ADDR and END_ADDR are free.  */
+                if (start == mmap_next_start) {
+                    mmap_next_start = addr;
+                }
+                return addr;
+            }
+        }
+    }
+}
+
+/*
+ * Find and reserve a free memory area of size 'size'. The search
+ * starts at 'start'.
+ * It must be called with mmap_lock() held.
+ * Return -1 if error.
+ */
+abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong align)
+{
+    void *ptr, *prev;
+    abi_ulong addr;
+    int wrapped, repeat;
+
+    align = MAX(align, qemu_host_page_size);
+
+    /* If 'start' == 0, then a default start address is used. */
+    if (start == 0) {
+        start = mmap_next_start;
+    } else {
+        start &= qemu_host_page_mask;
+    }
+    start = ROUND_UP(start, align);
+
+    size = HOST_PAGE_ALIGN(size);
+
+    if (reserved_va) {
+        return mmap_find_vma_reserved(start, size, align);
+    }
+
+    addr = start;
+    wrapped = repeat = 0;
+    prev = 0;
+
+    for (;; prev = ptr) {
+        /*
+         * Reserve needed memory area to avoid a race.
+         * It should be discarded using:
+         *  - mmap() with MAP_FIXED flag
+         *  - mremap() with MREMAP_FIXED flag
+         *  - shmat() with SHM_REMAP flag
+         */
+        ptr = mmap(g2h_untagged(addr), size, PROT_NONE,
+                   MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE, -1, 0);
+
+        /* ENOMEM, if host address space has no memory */
+        if (ptr == MAP_FAILED) {
+            return (abi_ulong)-1;
+        }
+
+        /* Count the number of sequential returns of the same address.
+           This is used to modify the search algorithm below.  */
+        repeat = (ptr == prev ? repeat + 1 : 0);
+
+        if (h2g_valid(ptr + size - 1)) {
+            addr = h2g(ptr);
+
+            if ((addr & (align - 1)) == 0) {
+                /* Success.  */
+                if (start == mmap_next_start && addr >= TASK_UNMAPPED_BASE) {
+                    mmap_next_start = addr + size;
+                }
+                return addr;
+            }
+
+            /* The address is not properly aligned for the target.  */
+            switch (repeat) {
+            case 0:
+                /* Assume the result that the kernel gave us is the
+                   first with enough free space, so start again at the
+                   next higher target page.  */
+                addr = ROUND_UP(addr, align);
+                break;
+            case 1:
+                /* Sometimes the kernel decides to perform the allocation
+                   at the top end of memory instead.  */
+                addr &= -align;
+                break;
+            case 2:
+                /* Start over at low memory.  */
+                addr = 0;
+                break;
+            default:
+                /* Fail.  This unaligned block must the last.  */
+                addr = -1;
+                break;
+            }
+        } else {
+            /* Since the result the kernel gave didn't fit, start
+               again at low memory.  If any repetition, fail.  */
+            addr = (repeat ? -1 : 0);
+        }
+
+        /* Unmap and try again.  */
+        munmap(ptr, size);
+
+        /* ENOMEM if we checked the whole of the target address space.  */
+        if (addr == (abi_ulong)-1) {
+            return (abi_ulong)-1;
+        } else if (addr == 0) {
+            if (wrapped) {
+                return (abi_ulong)-1;
+            }
+            wrapped = 1;
+            /* Don't actually use 0 when wrapping, instead indicate
+               that we'd truly like an allocation in low memory.  */
+            addr = (mmap_min_addr > TARGET_PAGE_SIZE
+                     ? TARGET_PAGE_ALIGN(mmap_min_addr)
+                     : TARGET_PAGE_SIZE);
+        } else if (wrapped && addr >= start) {
+            return (abi_ulong)-1;
+        }
+    }
+}
+
+/* NOTE: all the constants are the HOST ones */
+abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
+                     int flags, int fd, abi_ulong offset)
+{
+    abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len;
+    int page_flags, host_prot;
+
+    mmap_lock();
+    trace_target_mmap(start, len, target_prot, flags, fd, offset);
+
+    if (!len) {
+        errno = EINVAL;
+        goto fail;
+    }
+
+    page_flags = validate_prot_to_pageflags(&host_prot, target_prot);
+    if (!page_flags) {
+        errno = EINVAL;
+        goto fail;
+    }
+
+    /* Also check for overflows... */
+    len = TARGET_PAGE_ALIGN(len);
+    if (!len) {
+        errno = ENOMEM;
+        goto fail;
+    }
+
+    if (offset & ~TARGET_PAGE_MASK) {
+        errno = EINVAL;
+        goto fail;
+    }
+
+    /*
+     * If we're mapping shared memory, ensure we generate code for parallel
+     * execution and flush old translations.  This will work up to the level
+     * supported by the host -- anything that requires EXCP_ATOMIC will not
+     * be atomic with respect to an external process.
+     */
+    if (flags & MAP_SHARED) {
+        CPUState *cpu = thread_cpu;
+        if (!(cpu->tcg_cflags & CF_PARALLEL)) {
+            cpu->tcg_cflags |= CF_PARALLEL;
+            tb_flush(cpu);
+        }
+    }
+
+    real_start = start & qemu_host_page_mask;
+    host_offset = offset & qemu_host_page_mask;
+
+    /* If the user is asking for the kernel to find a location, do that
+       before we truncate the length for mapping files below.  */
+    if (!(flags & MAP_FIXED)) {
+        host_len = len + offset - host_offset;
+        host_len = HOST_PAGE_ALIGN(host_len);
+        start = mmap_find_vma(real_start, host_len, TARGET_PAGE_SIZE);
+        if (start == (abi_ulong)-1) {
+            errno = ENOMEM;
+            goto fail;
+        }
+    }
+
+    /* When mapping files into a memory area larger than the file, accesses
+       to pages beyond the file size will cause a SIGBUS. 
+
+       For example, if mmaping a file of 100 bytes on a host with 4K pages
+       emulating a target with 8K pages, the target expects to be able to
+       access the first 8K. But the host will trap us on any access beyond
+       4K.  
+
+       When emulating a target with a larger page-size than the hosts, we
+       may need to truncate file maps at EOF and add extra anonymous pages
+       up to the targets page boundary.  */
+
+    if ((qemu_real_host_page_size < qemu_host_page_size) &&
+        !(flags & MAP_ANONYMOUS)) {
+        struct stat sb;
+
+       if (fstat (fd, &sb) == -1)
+           goto fail;
+
+       /* Are we trying to create a map beyond EOF?.  */
+       if (offset + len > sb.st_size) {
+           /* If so, truncate the file map at eof aligned with 
+              the hosts real pagesize. Additional anonymous maps
+              will be created beyond EOF.  */
+           len = REAL_HOST_PAGE_ALIGN(sb.st_size - offset);
+       }
+    }
+
+    if (!(flags & MAP_FIXED)) {
+        unsigned long host_start;
+        void *p;
+
+        host_len = len + offset - host_offset;
+        host_len = HOST_PAGE_ALIGN(host_len);
+
+        /* Note: we prefer to control the mapping address. It is
+           especially important if qemu_host_page_size >
+           qemu_real_host_page_size */
+        p = mmap(g2h_untagged(start), host_len, host_prot,
+                 flags | MAP_FIXED | MAP_ANONYMOUS, -1, 0);
+        if (p == MAP_FAILED) {
+            goto fail;
+        }
+        /* update start so that it points to the file position at 'offset' */
+        host_start = (unsigned long)p;
+        if (!(flags & MAP_ANONYMOUS)) {
+            p = mmap(g2h_untagged(start), len, host_prot,
+                     flags | MAP_FIXED, fd, host_offset);
+            if (p == MAP_FAILED) {
+                munmap(g2h_untagged(start), host_len);
+                goto fail;
+            }
+            host_start += offset - host_offset;
+        }
+        start = h2g(host_start);
+    } else {
+        if (start & ~TARGET_PAGE_MASK) {
+            errno = EINVAL;
+            goto fail;
+        }
+        end = start + len;
+        real_end = HOST_PAGE_ALIGN(end);
+
+        /*
+         * Test if requested memory area fits target address space
+         * It can fail only on 64-bit host with 32-bit target.
+         * On any other target/host host mmap() handles this error correctly.
+         */
+        if (end < start || !guest_range_valid_untagged(start, len)) {
+            errno = ENOMEM;
+            goto fail;
+        }
+
+        /* worst case: we cannot map the file because the offset is not
+           aligned, so we read it */
+        if (!(flags & MAP_ANONYMOUS) &&
+            (offset & ~qemu_host_page_mask) != (start & ~qemu_host_page_mask)) {
+            /* msync() won't work here, so we return an error if write is
+               possible while it is a shared mapping */
+            if ((flags & MAP_TYPE) == MAP_SHARED &&
+                (host_prot & PROT_WRITE)) {
+                errno = EINVAL;
+                goto fail;
+            }
+            retaddr = target_mmap(start, len, target_prot | PROT_WRITE,
+                                  MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
+                                  -1, 0);
+            if (retaddr == -1)
+                goto fail;
+            if (pread(fd, g2h_untagged(start), len, offset) == -1)
+                goto fail;
+            if (!(host_prot & PROT_WRITE)) {
+                ret = target_mprotect(start, len, target_prot);
+                assert(ret == 0);
+            }
+            goto the_end;
+        }
+        
+        /* handle the start of the mapping */
+        if (start > real_start) {
+            if (real_end == real_start + qemu_host_page_size) {
+                /* one single host page */
+                ret = mmap_frag(real_start, start, end,
+                                host_prot, flags, fd, offset);
+                if (ret == -1)
+                    goto fail;
+                goto the_end1;
+            }
+            ret = mmap_frag(real_start, start, real_start + qemu_host_page_size,
+                            host_prot, flags, fd, offset);
+            if (ret == -1)
+                goto fail;
+            real_start += qemu_host_page_size;
+        }
+        /* handle the end of the mapping */
+        if (end < real_end) {
+            ret = mmap_frag(real_end - qemu_host_page_size,
+                            real_end - qemu_host_page_size, end,
+                            host_prot, flags, fd,
+                            offset + real_end - qemu_host_page_size - start);
+            if (ret == -1)
+                goto fail;
+            real_end -= qemu_host_page_size;
+        }
+
+        /* map the middle (easier) */
+        if (real_start < real_end) {
+            void *p;
+            unsigned long offset1;
+            if (flags & MAP_ANONYMOUS)
+                offset1 = 0;
+            else
+                offset1 = offset + real_start - start;
+            p = mmap(g2h_untagged(real_start), real_end - real_start,
+                     host_prot, flags, fd, offset1);
+            if (p == MAP_FAILED)
+                goto fail;
+        }
+    }
+ the_end1:
+    if (flags & MAP_ANONYMOUS) {
+        page_flags |= PAGE_ANON;
+    }
+    page_flags |= PAGE_RESET;
+    page_set_flags(start, start + len, page_flags);
+ the_end:
+    trace_target_mmap_complete(start);
+    if (qemu_loglevel_mask(CPU_LOG_PAGE)) {
+        log_page_dump(__func__);
+    }
+    tb_invalidate_phys_range(start, start + len);
+    mmap_unlock();
+    return start;
+fail:
+    mmap_unlock();
+    return -1;
+}
+
+static void mmap_reserve(abi_ulong start, abi_ulong size)
+{
+    abi_ulong real_start;
+    abi_ulong real_end;
+    abi_ulong addr;
+    abi_ulong end;
+    int prot;
+
+    real_start = start & qemu_host_page_mask;
+    real_end = HOST_PAGE_ALIGN(start + size);
+    end = start + size;
+    if (start > real_start) {
+        /* handle host page containing start */
+        prot = 0;
+        for (addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
+            prot |= page_get_flags(addr);
+        }
+        if (real_end == real_start + qemu_host_page_size) {
+            for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
+                prot |= page_get_flags(addr);
+            }
+            end = real_end;
+        }
+        if (prot != 0)
+            real_start += qemu_host_page_size;
+    }
+    if (end < real_end) {
+        prot = 0;
+        for (addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
+            prot |= page_get_flags(addr);
+        }
+        if (prot != 0)
+            real_end -= qemu_host_page_size;
+    }
+    if (real_start != real_end) {
+        mmap(g2h_untagged(real_start), real_end - real_start, PROT_NONE,
+                 MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE,
+                 -1, 0);
+    }
+}
+
+int target_munmap(abi_ulong start, abi_ulong len)
+{
+    abi_ulong end, real_start, real_end, addr;
+    int prot, ret;
+
+    trace_target_munmap(start, len);
+
+    if (start & ~TARGET_PAGE_MASK)
+        return -TARGET_EINVAL;
+    len = TARGET_PAGE_ALIGN(len);
+    if (len == 0 || !guest_range_valid_untagged(start, len)) {
+        return -TARGET_EINVAL;
+    }
+
+    mmap_lock();
+    end = start + len;
+    real_start = start & qemu_host_page_mask;
+    real_end = HOST_PAGE_ALIGN(end);
+
+    if (start > real_start) {
+        /* handle host page containing start */
+        prot = 0;
+        for(addr = real_start; addr < start; addr += TARGET_PAGE_SIZE) {
+            prot |= page_get_flags(addr);
+        }
+        if (real_end == real_start + qemu_host_page_size) {
+            for(addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
+                prot |= page_get_flags(addr);
+            }
+            end = real_end;
+        }
+        if (prot != 0)
+            real_start += qemu_host_page_size;
+    }
+    if (end < real_end) {
+        prot = 0;
+        for(addr = end; addr < real_end; addr += TARGET_PAGE_SIZE) {
+            prot |= page_get_flags(addr);
+        }
+        if (prot != 0)
+            real_end -= qemu_host_page_size;
+    }
+
+    ret = 0;
+    /* unmap what we can */
+    if (real_start < real_end) {
+        if (reserved_va) {
+            mmap_reserve(real_start, real_end - real_start);
+        } else {
+            ret = munmap(g2h_untagged(real_start), real_end - real_start);
+        }
+    }
+
+    if (ret == 0) {
+        page_set_flags(start, start + len, 0);
+        tb_invalidate_phys_range(start, start + len);
+    }
+    mmap_unlock();
+    return ret;
+}
+
+abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
+                       abi_ulong new_size, unsigned long flags,
+                       abi_ulong new_addr)
+{
+    int prot;
+    void *host_addr;
+
+    if (!guest_range_valid_untagged(old_addr, old_size) ||
+        ((flags & MREMAP_FIXED) &&
+         !guest_range_valid_untagged(new_addr, new_size)) ||
+        ((flags & MREMAP_MAYMOVE) == 0 &&
+         !guest_range_valid_untagged(old_addr, new_size))) {
+        errno = ENOMEM;
+        return -1;
+    }
+
+    mmap_lock();
+
+    if (flags & MREMAP_FIXED) {
+        host_addr = mremap(g2h_untagged(old_addr), old_size, new_size,
+                           flags, g2h_untagged(new_addr));
+
+        if (reserved_va && host_addr != MAP_FAILED) {
+            /* If new and old addresses overlap then the above mremap will
+               already have failed with EINVAL.  */
+            mmap_reserve(old_addr, old_size);
+        }
+    } else if (flags & MREMAP_MAYMOVE) {
+        abi_ulong mmap_start;
+
+        mmap_start = mmap_find_vma(0, new_size, TARGET_PAGE_SIZE);
+
+        if (mmap_start == -1) {
+            errno = ENOMEM;
+            host_addr = MAP_FAILED;
+        } else {
+            host_addr = mremap(g2h_untagged(old_addr), old_size, new_size,
+                               flags | MREMAP_FIXED,
+                               g2h_untagged(mmap_start));
+            if (reserved_va) {
+                mmap_reserve(old_addr, old_size);
+            }
+        }
+    } else {
+        int prot = 0;
+        if (reserved_va && old_size < new_size) {
+            abi_ulong addr;
+            for (addr = old_addr + old_size;
+                 addr < old_addr + new_size;
+                 addr++) {
+                prot |= page_get_flags(addr);
+            }
+        }
+        if (prot == 0) {
+            host_addr = mremap(g2h_untagged(old_addr),
+                               old_size, new_size, flags);
+
+            if (host_addr != MAP_FAILED) {
+                /* Check if address fits target address space */
+                if (!guest_range_valid_untagged(h2g(host_addr), new_size)) {
+                    /* Revert mremap() changes */
+                    host_addr = mremap(g2h_untagged(old_addr),
+                                       new_size, old_size, flags);
+                    errno = ENOMEM;
+                    host_addr = MAP_FAILED;
+                } else if (reserved_va && old_size > new_size) {
+                    mmap_reserve(old_addr + old_size, old_size - new_size);
+                }
+            }
+        } else {
+            errno = ENOMEM;
+            host_addr = MAP_FAILED;
+        }
+    }
+
+    if (host_addr == MAP_FAILED) {
+        new_addr = -1;
+    } else {
+        new_addr = h2g(host_addr);
+        prot = page_get_flags(old_addr);
+        page_set_flags(old_addr, old_addr + old_size, 0);
+        page_set_flags(new_addr, new_addr + new_size,
+                       prot | PAGE_VALID | PAGE_RESET);
+    }
+    tb_invalidate_phys_range(new_addr, new_addr + new_size);
+    mmap_unlock();
+    return new_addr;
+}