Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
Message-ID: <87c26050-9242-e6fb-3fce-b6bde815f76a@redhat.com>
Date:   Sat, 11 Dec 2021 02:31:42 +0100
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Subject: Re: [PATCH 15/19] kvm: x86: Save and restore guest XFD_ERR properly
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To:     Thomas Gleixner <tglx@linutronix.de>,
        Yang Zhong <yang.zhong@intel.com>, x86@kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com
Cc:     seanjc@google.com, jun.nakajima@intel.com, kevin.tian@intel.com,
        jing2.liu@linux.intel.com, jing2.liu@intel.com
References: <20211208000359.2853257-1-yang.zhong@intel.com>
 <20211208000359.2853257-16-yang.zhong@intel.com> <87pmq4vw54.ffs@tglx>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <87pmq4vw54.ffs@tglx>
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On 12/11/21 01:10, Thomas Gleixner wrote:
>      2) When the guest triggers #NM is takes an VMEXIT and the host
>         does:
> 
>                  rdmsrl(MSR_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
> 
>         injects the #NM and goes on.
> 
>      3) When the guest writes to MSR_XFD_ERR it takes an VMEXIT and
>         the host does:
> 
>             vcpu->arch.guest_fpu.xfd_err = msrval;
>             wrmsrl(MSR_XFD_ERR, msrval);

No wrmsrl here I think, the host value is 0 and should stay so.  Instead 
the wrmsrl will happen the next time the VCPU loop is entred.

Paolo