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From: Andrew Jones <drjones@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: quintela@redhat.com, QEMU Developers <qemu-devel@nongnu.org>,
	qemu-arm <qemu-arm@nongnu.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	kvmarm@lists.cs.columbia.edu, dgilbert@redhat.com
Subject: Re: [PATCH v4 1/2] target/arm: kvm: Handle DABT with no valid ISS
Date: Fri, 17 Apr 2020 15:10:32 +0200	[thread overview]
Message-ID: <20200417131032.lcyunbjwofsn2nzz@kamzik.brq.redhat.com> (raw)
In-Reply-To: <CAFEAcA_uWS+cVRk=BKra8AhsD+B1syVzhXeCMttSKwQDdo=j3w@mail.gmail.com>

On Fri, Apr 17, 2020 at 11:39:25AM +0100, Peter Maydell wrote:
> On Mon, 23 Mar 2020 at 11:32, Beata Michalska
> <beata.michalska@linaro.org> wrote:
> >
> > On ARMv7 & ARMv8 some load/store instructions might trigger a data abort
> > exception with no valid ISS info to be decoded. The lack of decode info
> > makes it at least tricky to emulate those instruction which is one of the
> > (many) reasons why KVM will not even try to do so.
> >
> > Add support for handling those by requesting KVM to inject external
> > dabt into the quest.
> >
> > Signed-off-by: Beata Michalska <beata.michalska@linaro.org>
> > ---
> >  target/arm/cpu.h     |  2 ++
> >  target/arm/kvm.c     | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  target/arm/kvm_arm.h | 11 +++++++++++
> >  3 files changed, 67 insertions(+)
> >
> > diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> > index 4ffd991..4f834c1 100644
> > --- a/target/arm/cpu.h
> > +++ b/target/arm/cpu.h
> > @@ -560,6 +560,8 @@ typedef struct CPUARMState {
> >          uint64_t esr;
> >      } serror;
> >
> > +    uint8_t ext_dabt_pending; /* Request for injecting ext DABT */
> 
> I was trying to work out whether we need to migrate this state,
> and I'm not sure. Andrew, do you know? I think this comes down
> to "at what points in QEMU's kvm run loop can migration kick in",
> and specifically if we get a KVM_EXIT_ARM_NISV do we definitely
> go round the loop and KVM_RUN again without ever checking
> to see if we should do a migration ?
>

I'd prefer a migration expert confirm this, so I've CC'ed David and Juan,
but afaict there's no way to break out of the KVM_RUN loop after a
successful (ret=0) call to kvm_arch_handle_exit() until after the next
KVM_RUN ioctl. This is because even if migration kicks the vcpus between
kvm_arch_handle_exit() and the next run, the signal won't do anything
other than prepare the vcpu for an immediate exit.

Thanks,
drew 

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  reply	other threads:[~2020-04-17 13:10 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-23 11:32 [PATCH v4 0/2] target/arm: kvm: Support for KVM DABT with no valid ISS Beata Michalska
2020-03-23 11:32 ` [PATCH v4 1/2] target/arm: kvm: Handle " Beata Michalska
2020-03-23 12:44   ` Andrew Jones
2020-03-25 15:15     ` Beata Michalska
2020-04-17 10:39   ` Peter Maydell
2020-04-17 13:10     ` Andrew Jones [this message]
2020-04-18 22:56       ` Beata Michalska
2020-04-24 12:16       ` Dr. David Alan Gilbert
2020-04-24 12:51         ` Peter Maydell
2020-04-25  9:24         ` Paolo Bonzini
2020-04-27  6:18           ` Andrew Jones
2020-03-23 11:32 ` [PATCH v4 2/2] target/arm: kvm: Handle potential issue with dabt injection Beata Michalska
2020-03-23 18:44   ` Richard Henderson
2020-03-25 15:16     ` Beata Michalska
2020-04-03  8:44   ` Andrew Jones
2020-04-07 11:24     ` Peter Maydell
2020-04-07 11:32       ` Beata Michalska
2020-04-07 11:31     ` Beata Michalska

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