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Subject: Re: [PATCH] KVM: vmx: Fix the broken usage of vmx_xsaves_supported
To:     Wanpeng Li <kernellwp@gmail.com>
Cc:     Xiaoyao Li <xiaoyao.li@linux.intel.com>,
        Tao Xu <tao3.xu@intel.com>, Radim Krcmar <rkrcmar@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, kvm <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20190620050301.1149-1-tao3.xu@intel.com>
 <CANRm+Cwg7ogTN1w=xNyn+8CfxwofdxRykULFe217pXidzEhh6Q@mail.gmail.com>
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 <CANRm+Cy_oo7BkYXD-nc0Ro=rivJircL6aheuFujMv6twS3gk=g@mail.gmail.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <165af492-027d-c640-9dea-c4c2d76fa1aa@redhat.com>
Date:   Thu, 20 Jun 2019 10:36:49 +0200
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On 20/06/19 10:27, Wanpeng Li wrote:
> Agreed, in addition, guest can enable/disable cpuid bits by grub
> parameter

Through what path?  Guest can disable X86_FEATURE_* but that's purely a
Linux feature, the few CPUID bits that can change at runtime already
call kvm_x86_ops->cpuid_update().

Paolo

> , should we call kvm_x86_ops->cpuid_update() in
> kvm_vcpu_reset() path to reflect the new guest cpuid influence to
> exec_control? e.g. the first boot guest disable xsaves in grub, kvm
> disables xsaves in exec_control; then guest reboot w/ xsaves enabled,
> it still get an #UD when executing.