From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     "Christopherson,, Sean" <seanjc@google.com>,
        "Liu, Jing2" <jing2.liu@intel.com>
CC:     "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "corbet@lwn.net" <corbet@lwn.net>,
        "shuah@kernel.org" <shuah@kernel.org>,
        "Nakajima, Jun" <jun.nakajima@intel.com>,
        "jing2.liu@linux.intel.com" <jing2.liu@linux.intel.com>,
        "Zeng, Guang" <guang.zeng@intel.com>,
        "Wang, Wei W" <wei.w.wang@intel.com>,
        "Zhong, Yang" <yang.zhong@intel.com>
Subject: RE: [PATCH v3 22/22] kvm: x86: Disable interception for IA32_XFD on
 demand
Thread-Topic: [PATCH v3 22/22] kvm: x86: Disable interception for IA32_XFD on
 demand
Thread-Index: AQHX9zE4gQJMQm2XFEKlfvGX4m1Fn6xIsbuAgABrvfA=
Date:   Wed, 29 Dec 2021 07:37:14 +0000
Message-ID: <BN9PR11MB5276B64A8F28FF23A71C949A8C449@BN9PR11MB5276.namprd11.prod.outlook.com>
References: <20211222124052.644626-1-jing2.liu@intel.com>
 <20211222124052.644626-23-jing2.liu@intel.com> <Ycu0KVq9PfuygKKx@google.com>
In-Reply-To: <Ycu0KVq9PfuygKKx@google.com>
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> From: Sean Christopherson <seanjc@google.com>
> Sent: Wednesday, December 29, 2021 9:05 AM
> > +	if (vcpu->arch.xfd_out_of_sync)
>=20
> Rather than adding a flag that tracks whether or not the MSR can be writt=
en
> by
> the guest, can't this be:
>=20
> 	if (!vmx_test_msr_bitmap_write(vcpu->loaded_vmcs->msr_bitmap))
> 		fpu_sync_guest_vmexit_xfd_state();
>=20

and forgot to mention a change different from above. It's in x86
common exit path but above is vmx specific check. I'm not sure
whether it's worthy of introducing another kvm_x86_ops callback
just for this minor usage.

Introducing an extra flag (e.g. vcpu->arch.xfd_disable_interception)
sounds simpler here.

Thanks
Kevin