linux-kernel - Re: [PATCH v3 22/22] kvm: x86: Disable interception for IA32

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Date:   Tue, 4 Jan 2022 18:58:09 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Jing Liu <jing2.liu@...el.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, corbet@....net, shuah@...nel.org,
        jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, guang.zeng@...el.com,
        wei.w.wang@...el.com, yang.zhong@...el.com
Subject: Re: [PATCH v3 22/22] kvm: x86: Disable interception for IA32_XFD on
 demand

On Tue, Jan 04, 2022, Paolo Bonzini wrote:
> On 12/29/21 02:04, Sean Christopherson wrote:
> > 
> > Speaking of nested, interception of #NM in vmx_update_exception_bitmap() is wrong
> > with respect to nested guests.  Until XFD is supported for L2, which I didn't see
> > in this series, #NM should not be intercepted while L2 is running.
> 
> Why wouldn't L2 support XFD, since there are no new VMCS bits?  As long as
> L0 knows what to do with XFD and XFD_ERR, it will do the right thing no
> matter if L1 or L2 is running.

I incorrectly assumed there was something L0 needed to do in order to support
nested XFD.