linux-kernel - Re: [PATCH v6 00/12] SVM cleanup and INVPCID feature support

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Message-ID: <CALMp9eQC5V_FQWGLUjc3pMziPeO0it_Mcm=L3bYcTMSEuFdGrA@mail.gmail.com>
Date:   Thu, 11 Mar 2021 13:23:47 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Babu Moger <babu.moger@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        kvm list <kvm@...r.kernel.org>, Joerg Roedel <joro@...tes.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Makarand Sonare <makarandsonare@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v6 00/12] SVM cleanup and INVPCID feature support

On Thu, Mar 11, 2021 at 12:32 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Thu, Mar 11, 2021 at 09:07:55PM +0100, Borislav Petkov wrote:
> > On Wed, Mar 10, 2021 at 07:21:23PM -0600, Babu Moger wrote:
> > > # git bisect good
> > > 59094faf3f618b2d2b2a45acb916437d611cede6 is the first bad commit
> > > commit 59094faf3f618b2d2b2a45acb916437d611cede6
> > > Author: Borislav Petkov <bp@...e.de>
> > > Date:   Mon Dec 25 13:57:16 2017 +0100
> > >
> > >     x86/kaiser: Move feature detection up
> >
> > What is the reproducer?
> >
> > Boot latest 4.9 stable kernel in a SEV guest? Can you send guest
> > .config?
> >
> > Upthread is talking about PCID, so I'm guessing host needs to be Zen3
> > with PCID. Anything else?
>
> That oops points to:
>
> [    1.237515] kernel BUG at /build/linux-dqnRSc/linux-4.9.228/arch/x86/kernel/alternative.c:709!
>
> which is:
>
>         local_flush_tlb();
>         sync_core();
>         /* Could also do a CLFLUSH here to speed up CPU recovery; but
>            that causes hangs on some VIA CPUs. */
>         for (i = 0; i < len; i++)
>                 BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);       <---
>         local_irq_restore(flags);
>         return addr;
>
> in text_poke() which basically says that the patching verification
> fails. And you have a local_flush_tlb() before that. And with PCID maybe
> it is not flushing properly or whatnot.
>
> And deep down in the TLB flushing code, it does:
>
>         if (kaiser_enabled)
>                 kaiser_flush_tlb_on_return_to_user();
>
> and that uses PCID...

I would expect kaiser_enabled to be false (and PCIDs not to be used),
since AMD CPUs are not vulnerable to Meltdown.