From: Jim Mattson <jmattson@google.com>
To: Jan Kiszka <jan.kiszka@web.de>
Cc: Oliver Upton <oupton@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>,
stable@vger.kernel.org
Subject: Re: [FYI PATCH 1/3] KVM: nVMX: Don't emulate instructions in guest mode
Date: Sat, 29 Feb 2020 12:17:37 -0800 [thread overview]
Message-ID: <CALMp9eR9zcXO64n7hDTzZHPkfV8qtuMHAbc=nLX8S8x7Crum+A@mail.gmail.com> (raw)
In-Reply-To: <e8fe4664-d948-f239-4ec9-82d9010b7d26@web.de>
Since UMIP emulation is broken, I'm not sure why anyone would use it.
(Sorry, Paolo.)
On Sat, Feb 29, 2020 at 11:21 AM Jan Kiszka <jan.kiszka@web.de> wrote:
>
> On 29.02.20 20:00, Jim Mattson wrote:
> > On Sat, Feb 29, 2020 at 10:33 AM Oliver Upton <oupton@google.com> wrote:
> >>
> >> Hi Jan,
> >>
> >> On Sat, Feb 29, 2020 at 10:00 AM Jan Kiszka <jan.kiszka@web.de> wrote:
> >>> Is this expected to cause regressions on less common workloads?
> >>> Jailhouse as L1 now fails when Linux as L2 tries to boot a CPU: L2-Linux
> >>> gets a triple fault on load_current_idt() in start_secondary(). Only
> >>> bisected so far, didn't debug further.
> >>
> >> I'm guessing that Jailhouse doesn't use 'descriptor table exiting', so
> >> when KVM gets the corresponding exit from L2 the emulation burden is
> >> on L0. We now refuse the emulation, which kicks a #UD back to L2. I
> >> can get a patch out quickly to address this case (like the PIO exiting
> >> one that came in this series) but the eventual solution is to map
> >> emulator intercept checks into VM-exits + call into the
> >> nested_vmx_exit_reflected() plumbing.
> >
> > If Jailhouse doesn't use descriptor table exiting, why is L0
> > intercepting descriptor table instructions? Is this just so that L0
> > can partially emulate UMIP on hardware that doesn't support it?
> >
>
> That seems to be the case: My host lacks umip, L1 has it. So, KVM is
> intercepting descriptor table load instructions to emulate umip.
> Jailhouse never activates that interception.
>
> Jan
next prev parent reply other threads:[~2020-02-29 20:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-24 18:56 [FYI PATCH 0/3] CVE-2020-2732 Paolo Bonzini
2020-02-24 18:56 ` [FYI PATCH 1/3] KVM: nVMX: Don't emulate instructions in guest mode Paolo Bonzini
2020-02-29 18:00 ` Jan Kiszka
2020-02-29 18:33 ` Oliver Upton
2020-02-29 19:00 ` Jim Mattson
2020-02-29 19:21 ` Jan Kiszka
2020-02-29 20:17 ` Jim Mattson [this message]
2020-02-29 20:36 ` Jan Kiszka
2020-02-24 18:56 ` [FYI PATCH 2/3] KVM: nVMX: Refactor IO bitmap checks into helper function Paolo Bonzini
2020-02-24 18:56 ` [FYI PATCH 3/3] KVM: nVMX: Check IO instruction VM-exit conditions Paolo Bonzini
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