From: Paolo Bonzini <pbonzini@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>,
"Wanpeng Li" <wanpeng.li@linux.intel.com>
Cc: Nadav Amit <nadav.amit@gmail.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/4] kvm: cpuid: fix the size of xsaves area
Date: Thu, 04 Dec 2014 16:49:10 +0100 [thread overview]
Message-ID: <54808276.9090309@redhat.com> (raw)
In-Reply-To: <20141204131454.GA17050@potion.brq.redhat.com>
On 04/12/2014 14:14, Radim Krčmář wrote:
> 2014-12-04 19:11+0800, Wanpeng Li:
>> The section of CPUID(EAX=0xd, ECX=1) in the spec which commit
>> f5c2290cd01e (KVM: cpuid: mask more bits in leaf 0xd and subleaves)
>> mentioned is older than SDM.
>>
>> EBX: Bits 31-00: The size in bytes of the XSAVE area containing all
>> states enabled by XCR0|IA32_XSS.
>
> Well, CPUs without XSAVES return 0 there, so we would emulate them
> incorrectly ... (I don't mind much, it is reserved.)
I agree it should stay to 0 if !XSAVES && !XSAVEC.
For !XSAVEC && XSAVES there's no silicon, so we have some leeway.
>> The the value of EBX should represent the size of XCR0 related XSAVE
>> area since IA32_XSS is not used currently.
>
> True, but 'supported' is not the state of XCR0, just its supremum.
> EBX should be set in kvm_update_cpuid(), like [3/4] does.
> (We can safely drop [2/4].)
Still, it's nice to be consistent and return a plausible value to
userspace for KVM_GET_SUPPORTED_CPUID.
Paolo
next prev parent reply other threads:[~2014-12-04 15:49 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-04 11:11 [PATCH v2 1/4] kvm: vmx: add nested virtualization support for xsaves Wanpeng Li
2014-12-04 11:11 ` [PATCH v2 2/4] kvm: cpuid: fix the size of xsaves area Wanpeng Li
2014-12-04 13:14 ` Radim Krčmář
2014-12-04 15:49 ` Paolo Bonzini [this message]
2014-12-04 16:41 ` Radim Krčmář
2014-12-04 11:11 ` [PATCH v2 3/4] kvm: cpuid: fix xsave area size of XSAVEC Wanpeng Li
2014-12-04 13:19 ` Radim Krčmář
2014-12-04 11:11 ` [PATCH v2 4/4] kvm: vmx: fix VMfailValid when write vmcs02/vmcs01 Wanpeng Li
2014-12-04 14:28 ` Paolo Bonzini
2014-12-04 14:17 ` [PATCH v2 1/4] kvm: vmx: add nested virtualization support for xsaves Paolo Bonzini
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