Re: [PATCH v4 1/2] target/arm: kvm: Handle DABT with no valid ISS

[Peter Maydell <peter.maydell@linaro.org>]

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 ?

thanks
-- PMM
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