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From: Andrew Scull <ascull@google.com>
To: James Morse <james.morse@arm.com>
Cc: kernel-team@android.com, catalin.marinas@arm.com, maz@kernel.org,
	will@kernel.org, kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 2/2] KVM: arm64: nVHE: Don't consume host SErrors with RAS
Date: Tue, 11 Aug 2020 15:43:04 +0100
Message-ID: <20200811144304.GA2917393@google.com> (raw)
In-Reply-To: <0cbb075a-ab5b-92a2-35bb-c3abb292ac84@arm.com>

On Wed, Aug 05, 2020 at 03:33:22PM +0100, James Morse wrote:
> Hi Andrew,
> 
> On 30/07/2020 16:18, Andrew Scull wrote:
> > The ESB at the start of the vectors causes any SErrors to be consumed to
> > DISR_EL1. If the exception came from the host and the ESB caught an
> > SError, it would not be noticed until a guest exits and DISR_EL1 is
> > checked. Further, the SError would be attributed to the guest and not
> > the host.
> 
> Yup, this happens because the world has moved underneath this code:

That's understandable!

> Previously any v8.2 RAS capable system would have been crazy to turn off VHE, so v8.0 and
> v8.1 systems had a nop here instead, and v8.2 systems had VHE, so there were no 'from the
> host' EL2 vectors.

RAS with nVHE is a buildable config and we're being foolish enough to
think about it so hopefully we can work something out :)

> > To avoid these problems, use a different exception vector for the host
> > that does not use an ESB but instead leaves any host SError pending. A
> > guest will not be entered if an SError is pending so it will always be
> > the host that will receive and handle it.
> > 
> > Hyp initialization is now passed the vector that is used for the host
> > and the vector for guests is stored in a percpu variable as
> > kvm_get_hyp_vector() is not suitable for calling from nVHE hyp.
> 
> > Fixes: 0e5b9c085dce ("KVM: arm64: Consume pending SError as early as possible")
> 
> Surely this can only happen if you had turned VHE off?

Correct, I'll make that clearer in the description.

> Thanks,
> 
> James
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Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-30 15:18 [PATCH 1/2] KVM: arm64: Restrict symbol aliasing to outside nVHE Andrew Scull
2020-07-30 15:18 ` [PATCH 2/2] KVM: arm64: nVHE: Don't consume host SErrors with RAS Andrew Scull
2020-07-30 16:02   ` Marc Zyngier
2020-07-30 16:25     ` Andrew Scull
2020-07-30 22:31   ` Andrew Scull
2020-07-31  8:00     ` Marc Zyngier
2020-07-31 10:20       ` Andrew Scull
2020-08-05 14:37         ` James Morse
2020-08-11 15:12           ` Andrew Scull
2020-08-26 17:41             ` James Morse
2020-08-05 14:34     ` James Morse
2020-08-11 14:53       ` Andrew Scull
2020-08-26 17:41         ` James Morse
2020-08-05 14:33   ` James Morse
2020-08-11 14:43     ` Andrew Scull [this message]

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