linux-kernel - Re: [PATCH 6/9] KVM: cpuid: mask more bits in leaf 0xd and subleaves

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Date:	Fri, 5 Dec 2014 08:34:47 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	rkrcmar@...hat.com
Subject: Re: [PATCH 6/9] KVM: cpuid: mask more bits in leaf 0xd and subleaves

Hi Paolo,
On Thu, Dec 04, 2014 at 04:57:11PM +0100, Paolo Bonzini wrote:
>- EAX=0Dh, ECX=1: output registers ECX/EDX are reserved.
>
>- EAX=0Dh, ECX>1: output register ECX bit 0 is clear for all the CPUID
>leaves we support, because variable "supported" comes from XCR0 and not
>XSS.  Bits above 0 are reserved, so ECX is overall zero.  Output register
>EDX is reserved.
>
>Source: Intel Architecture Instruction Set Extensions Programming
>Reference, ref. number 319433-022
>
>Reviewed-by: Radim Krčmář <rkrcmar@...hat.com>
>Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>---
> arch/x86/kvm/cpuid.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>

Do you miss this in your patch?

+       /* cpuid 0xD.1.eax */
+       const u32 kvm_supported_word10_x86_features =
+               F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1);
+

In addition, there is bisect issue if this is added in this patch.
(4/9 will take advantage of kvm_supported_word10_x86_features)

Regards,
Wanpeng Li 

>diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>index 2f7bc2de9915..644bfe828ce1 100644
>--- a/arch/x86/kvm/cpuid.c
>+++ b/arch/x86/kvm/cpuid.c
>@@ -482,8 +482,14 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> 					entry[i].ebx =
> 						xstate_required_size(supported,
> 								     true);
>-			} else if (entry[i].eax == 0 || !(supported & mask))
>-				continue;
>+			} else {
>+				if (entry[i].eax == 0 || !(supported & mask))
>+					continue;
>+				if (WARN_ON_ONCE(entry[i].ecx & 1))
>+					continue;
>+			}
>+			entry[i].ecx = 0;
>+			entry[i].edx = 0;
> 			entry[i].flags |=
> 			       KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
> 			++*nent;
>-- 
>1.8.3.1
>
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