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

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Message-ID: <20210311203206.GF5829@zn.tnic>
Date:   Thu, 11 Mar 2021 21:32:06 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Babu Moger <babu.moger@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.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 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...

Anyway, needs more info.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette