linux-kernel - Re: [PATCH 1/4] KVM: X86: Fix tlb flush for tdp in kvm_invalidate

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALMp9eSAYYL2T_H5b3Kv+OE2KgDz_iC32yQfpiqhwspRUezQ2w@mail.gmail.com>
Date:   Thu, 21 Oct 2021 10:32:49 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/4] KVM: X86: Fix tlb flush for tdp in kvm_invalidate_pcid()

On Thu, Oct 21, 2021 at 10:13 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 21/10/21 16:52, Sean Christopherson wrote:
> >> I think the EPT violation happens*after*  the cr3 write.  So the instruction to be
> >> emulated is not "cr3 write".  The emulation will queue fault into guest though,
> >> recursive EPT violation happens since the cr3 exceeds maxphyaddr limit.
> > Doh, you're correct.  I think my mind wandered into thinking about what would
> > happen with PDPTRs and forgot to get back to normal MOV CR3.
> >
> > So yeah, the only way to correctly handle this would be to intercept CR3 loads.
> > I'm guessing that would have a noticeable impact on guest performance.
>
> Ouch... yeah, allow_smaller_maxphyaddr already has bad performance, but
> intercepting CR3 loads would be another kind of slow.

Can we kill it? It's only half-baked as it is. Or are we committed to it now?