linux-kernel - Re: [PATCH v2] x86/cpu: Fix migration safety with X86_BUG_NULL

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Message-ID: <YW3TdmEe/mx/5aOO@google.com>
Date:   Mon, 18 Oct 2021 20:05:10 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Jane Malalane <jane.malalane@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Pu Wen <puwen@...on.cn>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Yazen Ghannam <Yazen.Ghannam@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Huang Rui <ray.huang@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Kim Phillips <kim.phillips@....com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] x86/cpu: Fix migration safety with X86_BUG_NULL_SEL

On Mon, Oct 18, 2021, Borislav Petkov wrote:
> On Mon, Oct 18, 2021 at 07:29:41PM +0000, Sean Christopherson wrote:
> > I agree.  If the argument for this patch is that the kernel can be migrated to
> > older hardware, then it stands to reason that the kernel could also be migrated
> > to a different CPU vendor entirely.  E.g. start on Intel, migrate to Zen1, kaboom.
> 
> Migration across vendors? Really, that works?
> 
> I'll believe it only when I see it with my own eyes.

There are plenty of caveats, but it is feasible.  KVM even has a few patches that
came about specifically to support cross-vendor migration, e.g. commit adc2a23734ac
("KVM: nSVM: improve SYSENTER emulation on AMD").