Re: [Xen-devel] [PATCH] address_space_translate: do not cross page boundaries

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

Il 30/01/2014 13:46, Stefano Stabellini ha scritto:
> The following commit:
>
> commit 149f54b53b7666a3facd45e86eece60ce7d3b114
> Author: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Date:   Fri May 24 12:59:37 2013 +0200
>
>     memory: add address_space_translate
>
> breaks Xen support in QEMU, in particular the Xen mapcache. The effect
> is that one Windows XP installation out of ten would end up with BSOD.
>
> The reason is that after this commit l in address_space_rw can span a
> page boundary, however qemu_get_ram_ptr still calls xen_map_cache asking
> to map a single page (if block->offset == 0).
>
> Fix the issue by reverting to the previous behaviour: do not return a
> length from address_space_translate_internal that can span a page
> boundary.
>
> Also in address_space_translate do not ignore the length returned by
> address_space_translate_internal.
>
> This patch should be backported to QEMU 1.6.x.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Signed-off-by: Anthony Perard <anthony.perard@xxxxxxxxxx>
Tested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: qemu-stable@xxxxxxxxxx

> ---
>  exec.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index 667a718..f3797b7 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -251,7 +251,7 @@ address_space_translate_internal(AddressSpaceDispatch *d, 
> hwaddr addr, hwaddr *x
>                                   hwaddr *plen, bool resolve_subpage)
>  {
>      MemoryRegionSection *section;
> -    Int128 diff;
> +    Int128 diff, diff_page;
>
>      section = address_space_lookup_region(d, addr, resolve_subpage);
>      /* Compute offset within MemoryRegionSection */
> @@ -260,7 +260,9 @@ address_space_translate_internal(AddressSpaceDispatch *d, 
> hwaddr addr, hwaddr *x
>      /* Compute offset within MemoryRegion */
>      *xlat = addr + section->offset_within_region;
>
> +    diff_page = int128_make64(((addr & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE) - 
> addr);
>      diff = int128_sub(section->mr->size, int128_make64(addr));
> +    diff = int128_min(diff, diff_page);
>      *plen = int128_get64(int128_min(diff, int128_make64(*plen)));
>      return section;
>  }
> @@ -275,7 +277,7 @@ MemoryRegion *address_space_translate(AddressSpace *as, 
> hwaddr addr,
>      hwaddr len = *plen;
>
>      for (;;) {
> -        section = address_space_translate_internal(as->dispatch, addr, &addr, 
> plen, true);
> +        section = address_space_translate_internal(as->dispatch, addr, &addr, 
> &len, true);
>          mr = section->mr;
>
>          if (!mr->iommu_ops) {

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