Xen devel - May 2006 - RE: [Xen-changelog] Fix MOVS instruction emulation for HVM MMIO.

> -----Original Message-----
> From: xen-changelog-bounces@lists.xensource.com 
> [mailto:xen-changelog-bounces@lists.xensource.com] On Behalf 
> Of Xen patchbot-unstable
> Sent: 16 May 2006 22:30
> To: xen-changelog@lists.xensource.com
> Subject: [Xen-changelog] Fix MOVS instruction emulation for HVM MMIO.
> 
> # HG changeset patch
> # User kaf24@firebug.cl.cam.ac.uk
> # Node ID 7fdc4a8b782b1e17fc473d418236ab44cc31b35f
> # Parent  aab3cd33d2ba65340d355ffbfc859ef6e7b64df3
> Fix MOVS instruction emulation for HVM MMIO.
> From: Gerd Hoffman
> Signed-off-by: Keir Fraser <keir@xensource.com>
> ---
>  xen/arch/x86/hvm/platform.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff -r aab3cd33d2ba -r 7fdc4a8b782b xen/arch/x86/hvm/platform.c
> --- a/xen/arch/x86/hvm/platform.c	Tue May 16 16:34:27 2006 +0100
> +++ b/xen/arch/x86/hvm/platform.c	Tue May 16 19:50:23 2006 +0100
> @@ -865,7 +865,7 @@ void handle_mmio(unsigned long va, unsig
>           * copy ourself. After this copy succeeds, "rep 
> movs" is executed
>           * again.
>           */
> -        if ((addr & PAGE_MASK) != ((addr + size - 1) & PAGE_MASK))
{
> +        if ((addr & PAGE_MASK) != ((addr + sign * (size - 1)) & 
> + PAGE_MASK)) {
With the risk of being wrong (again), I''d say this is incorrect: The
MOVS instruction will start reading at ESI, and write at the address
indicated by EDI and write with size bytes, even when it''s copying
backwards. So there should be no multiplication of sign on this line. 

I''m sorry I missed this the first time I looked at the patch the first
time and said "That looks right". 

The rest of the patch looks fine to me.

--
Mats
>              unsigned long value = 0;
>  
>              mmio_opp->flags |= OVERLAP; @@ -876,7 +876,7 @@ 
> void handle_mmio(unsigned long va, unsig
>                  hvm_copy(&value, addr, size, HVM_COPY_IN);
>              send_mmio_req(IOREQ_TYPE_COPY, gpa, 1, size, 
> value, dir, 0);
>          } else {
> -            if ((addr & PAGE_MASK) != ((addr + count * size 
> - 1) & PAGE_MASK)) {
> +            if ((addr & PAGE_MASK) != ((addr + sign * (count 
> * size - 
> + 1)) & PAGE_MASK)) {
>                  regs->eip -= inst_len; /* do not advance %eip */
>  
>                  if (sign > 0)
> 
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> 
> 

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Petersson, Mats wrote:
>> Subject: [Xen-changelog] Fix MOVS instruction emulation for HVM MMIO.
>>
>> diff -r aab3cd33d2ba -r 7fdc4a8b782b xen/arch/x86/hvm/platform.c
>> --- a/xen/arch/x86/hvm/platform.c	Tue May 16 16:34:27 2006 +0100
>> +++ b/xen/arch/x86/hvm/platform.c	Tue May 16 19:50:23 2006 +0100
>> @@ -865,7 +865,7 @@ void handle_mmio(unsigned long va, unsig
>>           * copy ourself. After this copy succeeds, "rep 
>> movs" is executed
>>           * again.
>>           */
>> -        if ((addr & PAGE_MASK) != ((addr + size - 1) &
PAGE_MASK)) {
>> +        if ((addr & PAGE_MASK) != ((addr + sign * (size - 1))
&
>> + PAGE_MASK)) {
> 
> With the risk of being wrong (again), I''d say this is incorrect:
The
> MOVS instruction will start reading at ESI, and write at the address
> indicated by EDI and write with size bytes, even when it''s copying
> backwards. So there should be no multiplication of sign on this line. 
I still think this is correct.  If I understand things correctly the
point of the test is to figure whenever the _next_ repz movs interation
will access another page (and if so copy just one data word and let the
emulator kick in again for the remaining data on the page above/below).

cheers,

  Gerd

-- 
Gerd Hoffmann <kraxel@suse.de>
Erst mal heiraten, ein, zwei Kinder, und wenn alles läuft
geh'' ich nach drei Jahren mit der Familie an die Börse.
http://www.suse.de/~kraxel/julika-dora.jpeg

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