Date:   Tue, 4 Jan 2022 18:58:09 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Jing Liu <jing2.liu@intel.com>, x86@kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, corbet@lwn.net, shuah@kernel.org,
        jun.nakajima@intel.com, kevin.tian@intel.com,
        jing2.liu@linux.intel.com, guang.zeng@intel.com,
        wei.w.wang@intel.com, yang.zhong@intel.com
Subject: Re: [PATCH v3 22/22] kvm: x86: Disable interception for IA32_XFD on
 demand
Message-ID: <YdSYwR5NDfJ6LIrU@google.com>
References: <20211222124052.644626-1-jing2.liu@intel.com>
 <20211222124052.644626-23-jing2.liu@intel.com>
 <Ycu0KVq9PfuygKKx@google.com>
 <ff29b36a-ffe4-8ba9-2856-cf96fcf33c0d@redhat.com>
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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.