linux-kernel - Re: [PATCH 16/28] KVM: VMX: Manually recalc all MSR intercepts on userspace MSR filter change

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Message-ID: <aEFAQW2HxUu0ynVr@intel.com>
Date: Thu, 5 Jun 2025 14:59:13 +0800
From: Chao Gao <chao.gao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...en8.de>, Xin Li
	<xin@...or.com>, Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH 16/28] KVM: VMX: Manually recalc all MSR intercepts on
 userspace MSR filter change

On Thu, May 29, 2025 at 04:40:01PM -0700, Sean Christopherson wrote:
>On a userspace MSR filter change, recalculate all MSR intercepts using the
>filter-agnostic logic instead of maintaining a "shadow copy" of KVM's
>desired intercepts.  The shadow bitmaps add yet another point of failure,
>are confusing (e.g. what does "handled specially" mean!?!?), an eyesore,
>and a maintenance burden.
>
>Given that KVM *must* be able to recalculate the correct intercepts at any
>given time, and that MSR filter updates are not hot paths, there is zero
>benefit to maintaining the shadow bitmaps.
>
>Link: https://lore.kernel.org/all/aCdPbZiYmtni4Bjs@google.com
>Link: https://lore.kernel.org/all/20241126180253.GAZ0YNTdXH1UGeqsu6@fat_crate.local
>Cc: Borislav Petkov <bp@...en8.de>
>Cc: Xin Li <xin@...or.com>
>Cc: Chao Gao <chao.gao@...el.com>
>Cc: Dapeng Mi <dapeng1.mi@...ux.intel.com>
>Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Chao Gao <chao.gao@...el.com>

one nit below,

>+
>+	if (vcpu->arch.xfd_no_write_intercept)
>+		vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD, MSR_TYPE_RW);
>+
>+

Remove one newline here.