linux-kernel - Re: [PATCH v2 4/7] KVM:CPUID: Fix xsaves area size calculation for CPUID.(EAX=0xD,ECX=1).

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Message-ID: <20190125224704.GD21849@linux.intel.com>
Date:   Fri, 25 Jan 2019 14:47:05 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com,
        yu-cheng.yu@...el.com, yi.z.zhang@...el.com, hjl.tools@...il.com,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v2 4/7] KVM:CPUID: Fix xsaves area size calculation for
 CPUID.(EAX=0xD,ECX=1).

On Wed, Jan 23, 2019 at 04:59:06AM +0800, Yang Weijiang wrote:
> According to latest Software Development Manual vol.2/3.2,
> for CPUID.(EAX=0xD,ECX=1), it should report xsaves area size
> containing all states enabled  by XCR0|IA32_MSR_XSS.
> 
> Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/kvm/cpuid.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index dbeb4e7904eb..67b464d1d749 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -136,7 +136,8 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>  
>  	best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
>  	if (best && (best->eax & (F(XSAVES) | F(XSAVEC))))
> -		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
> +		best->ebx = xstate_required_size(vcpu->arch.xcr0 |
> +			    kvm_supported_xss(), true);

kvm_supported_xss() provides the wrong value, that's what's *supported*.
CPUID reflects what's actually enabled, e.g. vcpu->arch.ia32_xss.

If you're going to bother adding spaces to align things, might as well
align the parameters, e.g.:

		best->ebx = xstate_required_size(vcpu->arch.xcr0 |
						 vcpu->arch.ia32_xss, true);

>  
>  	/*
>  	 * The existing code assumes virtual address is 48-bit or 57-bit in the
> -- 
> 2.17.1
>