Re: [PATCH v2] linux-user: Undo incomplete mmap

[Akihiko Odaki <akihiko.odaki@daynix.com>]

On 2023/09/03 14:39, Akihiko Odaki wrote:
> When the host page size is greater than the target page size and
> MAP_FIXED or MAP_FIXED_NOREPLACE is requested, mmap will be done for
> three parts: start, middle, and end. If a later part of mmap fail,
> mmap done in the earlier parts must be reverted.
> 
> Fixes: 54936004fd ("mmap emulation")
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
> V1 -> V2: Rebased.
> 
>   linux-user/mmap.c | 65 +++++++++++++++++++++++++++++------------------
>   1 file changed, 40 insertions(+), 25 deletions(-)
> 
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index 9aab48d4a3..72521f8d27 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -224,13 +224,15 @@ int target_mprotect(abi_ulong start, abi_ulong len, int target_prot)
>   
>   /* map an incomplete host page */
>   static bool mmap_frag(abi_ulong real_start, abi_ulong start, abi_ulong last,
> -                      int prot, int flags, int fd, off_t offset)
> +                      int prot, int flags, int fd, off_t offset, bool *mapped)
>   {
>       abi_ulong real_last;
>       void *host_start;
>       int prot_old, prot_new;
>       int host_prot_old, host_prot_new;
>   
> +    *mapped = false;
> +
>       if (!(flags & MAP_ANONYMOUS)
>           && (flags & MAP_TYPE) == MAP_SHARED
>           && (prot & PROT_WRITE)) {
> @@ -271,6 +273,7 @@ static bool mmap_frag(abi_ulong real_start, abi_ulong start, abi_ulong last,
>               return false;
>           }
>           prot_old = prot;
> +        *mapped = true;
>       }
>       prot_new = prot | prot_old;
>   
> @@ -448,7 +451,7 @@ abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong align)
>   abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
>                        int flags, int fd, off_t offset)
>   {
> -    abi_ulong ret, last, real_start, real_last, retaddr, host_len;
> +    abi_ulong ret, last, real_start, retaddr, host_len;
>       abi_ulong passthrough_start = -1, passthrough_last = 0;
>       int page_flags;
>       off_t host_offset;
> @@ -577,12 +580,16 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
>           passthrough_start = start;
>           passthrough_last = last;
>       } else {
> +        abi_ulong middle_start = HOST_PAGE_ALIGN(start);
> +        abi_ulong middle_last = ((start + len) & qemu_host_page_mask) - 1;
> +        abi_ulong mapped_len = 0;
> +        bool mapped;
> +
>           if (start & ~TARGET_PAGE_MASK) {
>               errno = EINVAL;
>               goto fail;
>           }
>           last = start + len - 1;
> -        real_last = HOST_PAGE_ALIGN(last) - 1;
>   
>           /*
>            * Test if requested memory area fits target address space
> @@ -649,35 +656,26 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
>           }
>   
>           /* handle the start of the mapping */
> -        if (start > real_start) {
> -            if (real_last == real_start + qemu_host_page_size - 1) {
> +        if (start < middle_start) {
> +            if (last < middle_start) {
>                   /* one single host page */
>                   if (!mmap_frag(real_start, start, last,
> -                               target_prot, flags, fd, offset)) {
> +                               target_prot, flags, fd, offset, &mapped)) {
>                       goto fail;
>                   }
>                   goto the_end1;
>               }
> -            if (!mmap_frag(real_start, start,
> -                           real_start + qemu_host_page_size - 1,
> -                           target_prot, flags, fd, offset)) {
> +            if (!mmap_frag(real_start, start, middle_start - 1,
> +                           target_prot, flags, fd, offset, &mapped)) {
>                   goto fail;
>               }
> -            real_start += qemu_host_page_size;
> -        }
> -        /* handle the end of the mapping */
> -        if (last < real_last) {
> -            abi_ulong real_page = real_last - qemu_host_page_size + 1;
> -            if (!mmap_frag(real_page, real_page, last,
> -                           target_prot, flags, fd,
> -                           offset + real_page - start)) {
> -                goto fail;
> +            if (mapped) {
> +                mapped_len = qemu_host_page_size;
>               }
> -            real_last -= qemu_host_page_size;
>           }
>   
>           /* map the middle (easier) */
> -        if (real_start < real_last) {
> +        if (middle_start < middle_last) {
>               void *p, *want_p;
>               off_t offset1;
>               size_t len1;
> @@ -685,10 +683,10 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
>               if (flags & MAP_ANONYMOUS) {
>                   offset1 = 0;
>               } else {
> -                offset1 = offset + real_start - start;
> +                offset1 = offset + middle_start - start;
>               }
> -            len1 = real_last - real_start + 1;
> -            want_p = g2h_untagged(real_start);
> +            len1 = middle_last - middle_start + 1;
> +            want_p = g2h_untagged(middle_start);
>   
>               p = mmap(want_p, len1, target_to_host_prot(target_prot),
>                        flags, fd, offset1);
> @@ -697,10 +695,27 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
>                       munmap(p, len1);
>                       errno = EEXIST;
>                   }
> +                if (mapped_len) {
> +                    munmap(g2h_untagged(middle_start - mapped_len), mapped_len);
> +                }
> +                goto fail;
> +            }
> +            mapped_len += len1;
> +            passthrough_start = middle_start;
> +            passthrough_last = middle_last;
> +        }
> +
> +        /* handle the end of the mapping */
> +        if (last > middle_last) {
> +            abi_ulong real_page = middle_last + 1;
> +            if (!mmap_frag(real_page, real_page, last,
> +                           target_prot, flags, fd,
> +                           offset + real_page - start, &mapped)) {
> +                if (mapped_len) {
> +                    munmap(g2h_untagged(real_page - mapped_len), mapped_len);
> +                }
>                   goto fail;
>               }
> -            passthrough_start = real_start;
> -            passthrough_last = real_last;
>           }
>       }
>    the_end1:

Hi Richard,

Can you have a look at this patch?

Regards,
Akihiko Odaki