linux-kernel - Re: [RFC PATCH v1 5/5] KVM: Remove kvm

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Message-ID: <e0ce7a92-f8e4-406c-a7dd-c59c8d541d0b@zytor.com>
Date: Wed, 17 Sep 2025 09:51:29 -0700
From: Xin Li <xin@...or.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-pm@...r.kernel.org, pbonzini@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, rafael@...nel.org, pavel@...nel.org,
        brgerst@...il.com, david.kaplan@....com, peterz@...radead.org,
        andrew.cooper3@...rix.com, kprateek.nayak@....com,
        arjan@...ux.intel.com, chao.gao@...el.com, rick.p.edgecombe@...el.com,
        dan.j.williams@...el.com
Subject: Re: [RFC PATCH v1 5/5] KVM: Remove kvm_rebooting and its references

On 9/16/2025 10:56 AM, Sean Christopherson wrote:
> On Tue, Sep 09, 2025, Xin Li (Intel) wrote:
>> Drop kvm_rebooting and all related uses.  Virtualization is now disabled
>> immediately before a CPU shuts down, eliminating any chance of executing
>> virtualization instructions during reboot.
> 
> Wrong.  KVM clears EFER.SVME in reponse to kvm_shutdown(), and thus can trip
> #UDs on e.g. VMRUN.
> 

This patch assumes that AMD SVM enable/disable has been moved to the CPU
startup and shutdown routines.  Accordingly, kvm_shutdown() no longer 
clears EFER.SVME, and the patch demonstrates the resulting simplification 
from removing kvm_rebooting.  However, as noted in the cover letter, no 
actual modifications were made to AMD SVM.

Is this what seems wrong to you?

Thanks!
     Xin