linux-kernel - Re: FSGSBASE causing panic on 5.9-rc1

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Message-ID: <aab48f12-5c2a-8e01-8dcb-16669fda7526@redhat.com>
Date:   Thu, 20 Aug 2020 15:43:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Joerg Roedel <joro@...tes.org>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sasha Levin <sashal@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: FSGSBASE causing panic on 5.9-rc1

On 19/08/20 23:25, Andy Lutomirski wrote:
>         wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gsbase);
>         load_gs_index(svm->host.gs);
> 
> Surely that should do load_gs_index() *before* wrmsrl().  But that's
> not the problem at hand.

The wrmsrl is writing the inactive GS base so the ordering between
load_gs_index and wrmsrl(MSR_KERNEL_GS_BASE) should be irrelevant?

Paolo