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 09:20:05 +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

On Fri, Dec 05, 2014 at 08:34:47AM +0800, Wanpeng Li wrote:
>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)

Also due to "kvm: x86: mask out XSAVES".

Regards,
Wanpeng Li

>
>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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