linux-kernel - Re: [PATCH] KVM: vmx: Fix the broken usage of vmx_xsaves

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Message-ID: <165af492-027d-c640-9dea-c4c2d76fa1aa@redhat.com>
Date:   Thu, 20 Jun 2019 10:36:49 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Xiaoyao Li <xiaoyao.li@...ux.intel.com>,
        Tao Xu <tao3.xu@...el.com>, Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, kvm <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: vmx: Fix the broken usage of vmx_xsaves_supported

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.