* [PATCH] x86emul: tighten CLFLUSH emulation
@ 2015-01-12 8:23 Jan Beulich
2015-01-12 11:04 ` Andrew Cooper
0 siblings, 1 reply; 2+ messages in thread
From: Jan Beulich @ 2015-01-12 8:23 UTC (permalink / raw)
To: xen-devel; +Cc: Andrew Cooper, Keir Fraser
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While for us it's not as bad as it was for Linux, their commit
13e457e0ee ("KVM: x86: Emulator does not decode clflush well", by
Nadav Amit <namit@cs.technion.ac.il>) nevertheless points out two
shortcomings in our code: opcode 0F AE /7 is clflush only when it uses
a memory mode (otherwise it's SFENCE) and when there's no REP prefix
(an operand size prefix is fine, as that's CLFLUSHOPT).
Signed-off-by: Jan Beulich <jbeulich@suse.com>
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -4400,7 +4400,9 @@ x86_emulate(
case 0xae: /* Grp15 */
switch ( modrm_reg & 7 )
{
- case 7: /* clflush */
+ case 7: /* clflush{,opt} */
+ fail_if(modrm_mod == 3);
+ fail_if(rep_prefix());
fail_if(ops->wbinvd == NULL);
if ( (rc = ops->wbinvd(ctxt)) != 0 )
goto done;
[-- Attachment #2: x86emul-clflush.patch --]
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x86emul: tighten CLFLUSH emulation
While for us it's not as bad as it was for Linux, their commit
13e457e0ee ("KVM: x86: Emulator does not decode clflush well", by
Nadav Amit <namit@cs.technion.ac.il>) nevertheless points out two
shortcomings in our code: opcode 0F AE /7 is clflush only when it uses
a memory mode (otherwise it's SFENCE) and when there's no REP prefix
(an operand size prefix is fine, as that's CLFLUSHOPT).
Signed-off-by: Jan Beulich <jbeulich@suse.com>
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -4400,7 +4400,9 @@ x86_emulate(
case 0xae: /* Grp15 */
switch ( modrm_reg & 7 )
{
- case 7: /* clflush */
+ case 7: /* clflush{,opt} */
+ fail_if(modrm_mod == 3);
+ fail_if(rep_prefix());
fail_if(ops->wbinvd == NULL);
if ( (rc = ops->wbinvd(ctxt)) != 0 )
goto done;
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^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] x86emul: tighten CLFLUSH emulation
2015-01-12 8:23 [PATCH] x86emul: tighten CLFLUSH emulation Jan Beulich
@ 2015-01-12 11:04 ` Andrew Cooper
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Cooper @ 2015-01-12 11:04 UTC (permalink / raw)
To: Jan Beulich, xen-devel; +Cc: Keir Fraser
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On 12/01/15 08:23, Jan Beulich wrote:
> While for us it's not as bad as it was for Linux, their commit
> 13e457e0ee ("KVM: x86: Emulator does not decode clflush well", by
> Nadav Amit <namit@cs.technion.ac.il>) nevertheless points out two
> shortcomings in our code: opcode 0F AE /7 is clflush only when it uses
> a memory mode (otherwise it's SFENCE) and when there's no REP prefix
> (an operand size prefix is fine, as that's CLFLUSHOPT).
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
>
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -4400,7 +4400,9 @@ x86_emulate(
> case 0xae: /* Grp15 */
> switch ( modrm_reg & 7 )
> {
> - case 7: /* clflush */
> + case 7: /* clflush{,opt} */
> + fail_if(modrm_mod == 3);
> + fail_if(rep_prefix());
> fail_if(ops->wbinvd == NULL);
> if ( (rc = ops->wbinvd(ctxt)) != 0 )
> goto done;
>
>
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
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Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
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2015-01-12 8:23 [PATCH] x86emul: tighten CLFLUSH emulation Jan Beulich
2015-01-12 11:04 ` Andrew Cooper
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