[PATCH]: KVM: Fix cmpxchg for writeback changes

[PATCH]: KVM: Fix cmpxchg for writeback changes

[Aurelien Jarno]

  KVM: Fix writeback for cmpxchg instruction

  The writeback fixes (02c03a326a5df825cc01de426f72e160db2b9538) broke
  cmpxchg emulation.  The patch below fixes that.

  Signed-off-by: Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 21ce977..9d30d10 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -1275,7 +1275,7 @@ twobyte_insn:
 		src.val = _regs[VCPU_REGS_RAX];
 		emulate_2op_SrcV("cmp", src, dst, _eflags);
 		/* Always write back. The question is: where to? */
-		d |= Mov;
+		no_wb = 0;
 		if (_eflags & EFLG_ZF) {
 			/* Success: write back to memory. */
 			dst.val = src.orig_val;

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org         | aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org
   `-    people.debian.org/~aurel32 | www.aurel32.net

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Re: [PATCH]: KVM: Fix cmpxchg for writeback changes

[Avi Kivity]

Aurelien Jarno wrote:
>   KVM: Fix writeback for cmpxchg instruction
>
>   The writeback fixes (02c03a326a5df825cc01de426f72e160db2b9538) broke
>   cmpxchg emulation.  The patch below fixes that.
>
>   Signed-off-by: Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>
>
> diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
> index 21ce977..9d30d10 100644
> --- a/drivers/kvm/x86_emulate.c
> +++ b/drivers/kvm/x86_emulate.c
> @@ -1275,7 +1275,7 @@ twobyte_insn:
>  		src.val = _regs[VCPU_REGS_RAX];
>  		emulate_2op_SrcV("cmp", src, dst, _eflags);
>  		/* Always write back. The question is: where to? */
> -		d |= Mov;
> +		no_wb = 0;
>  		if (_eflags & EFLG_ZF) {
>  			/* Success: write back to memory. */
>  			dst.val = src.orig_val;
>
>   

But no_wb defaults to zero?


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: [PATCH]: KVM: Fix cmpxchg for writeback changes

[Aurelien Jarno]

On Wed, Jul 25, 2007 at 12:34:02PM +0300, Avi Kivity wrote:
> Aurelien Jarno wrote:
> >   KVM: Fix writeback for cmpxchg instruction
> >
> >   The writeback fixes (02c03a326a5df825cc01de426f72e160db2b9538) broke
> >   cmpxchg emulation.  The patch below fixes that.
> >
> >   Signed-off-by: Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>
> >

[snip]

> But no_wb defaults to zero?

Oops right. So please find a new patch below.

  KVM: Remove dead code in the cmpxchg instruction emulation

  The writeback fixes (02c03a326a5df825cc01de426f72e160db2b9538) let
  some dead code in the cmpxchg instruction emulation. Remove it.

  Signed-off-by: Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 21ce977..7b1baec 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -1274,8 +1274,6 @@ twobyte_insn:
 		src.orig_val = src.val;
 		src.val = _regs[VCPU_REGS_RAX];
 		emulate_2op_SrcV("cmp", src, dst, _eflags);
-		/* Always write back. The question is: where to? */
-		d |= Mov;
 		if (_eflags & EFLG_ZF) {
 			/* Success: write back to memory. */
 			dst.val = src.orig_val;

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org         | aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org
   `-    people.debian.org/~aurel32 | www.aurel32.net

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Re: [PATCH]: KVM: Fix cmpxchg for writeback changes

[Avi Kivity]

Aurelien Jarno wrote:
>   KVM: Remove dead code in the cmpxchg instruction emulation
>
>   The writeback fixes (02c03a326a5df825cc01de426f72e160db2b9538) let
>   some dead code in the cmpxchg instruction emulation. Remove it.
>
>   Signed-off-by: Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>
>
>   

Applied, thanks.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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