linux-kernel - Re: [PATCH] KVM: VMX: Flush shadow VMCS on emergency reboot

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Message-ID: <9ffccab8-5e77-4e55-bd92-f31058600e9f@intel.com>
Date: Mon, 14 Apr 2025 14:24:32 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] KVM: VMX: Flush shadow VMCS on emergency reboot

On 4/12/2025 12:57 AM, Sean Christopherson wrote:
>> If a VMM wants to leverage the VMXOFF behavior, software enumeration
>> might be needed for nested virtualization. Using CPU F/M/S (SPR+) to
>> enumerate a behavior could be problematic for virtualization. Right?
> Yeah, F/M/S is a bad idea.  Architecturally, I think the behavior needs to be
> tied to support for SEAM.  Is there a safe-ish way to probe for SEAM support,
> without having to glean it from MSR_IA32_MKTME_KEYID_PARTITIONING?

yes, the bit 15 of MSR_IA32_MTRRCAP.