linux-kernel - Re: [PATCH 2/2] KVM: VMX: Drop unnecessary vmx_fb_clear_ctrl

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Message-ID: <20230607202038.5vsgsrt724qhxnjd@desk>
Date:   Wed, 7 Jun 2023 13:20:38 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chao Gao <chao.gao@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 2/2] KVM: VMX: Drop unnecessary
 vmx_fb_clear_ctrl_available "cache"

On Tue, Jun 06, 2023 at 05:43:10PM -0700, Sean Christopherson wrote:
> Now that KVM snapshots the host's MSR_IA32_ARCH_CAPABILITIES, drop the
> similar snapshot/cache of whether or not KVM is allowed to manipulate
> ARCH_CAPABILITIES.FB_CLEAR_CTRL.  The motivation for the cache was

FB_CLEAR_CTRL is a read-only bit, I think you mean
MSR_IA32_MCU_OPT_CTRL.FB_CLEAR_DIS.

> presumably to avoid the RDMSR, e.g. boot_cpu_has_bug() is quite cheap, and
> modifying the vCPU's MSR_IA32_ARCH_CAPABILITIES is an infrequent option
> and a relatively slow path.
> 
> Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

LGTM.

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>