Re: [PATCH v6 12/13] KVM: arm64: Handle RAS SErrors from EL2 on guest exit

[Christoffer Dall <christoffer.dall@linaro.org>]

On Mon, Jan 15, 2018 at 07:39:05PM +0000, James Morse wrote:
> We expect to have firmware-first handling of RAS SErrors, with errors
> notified via an APEI method. For systems without firmware-first, add
> some minimal handling to KVM.
> 
> There are two ways KVM can take an SError due to a guest, either may be a
> RAS error: we exit the guest due to an SError routed to EL2 by HCR_EL2.AMO,
> or we take an SError from EL2 when we unmask PSTATE.A from __guest_exit.
> 
> The current SError from EL2 code unmasks SError and tries to fence any
> pending SError into a single instruction window. It then leaves SError
> unmasked.
> 
> With the v8.2 RAS Extensions we may take an SError for a 'corrected'
> error, but KVM is only able to handle SError from EL2 if they occur
> during this single instruction window...
> 
> The RAS Extensions give us a new instruction to synchronise and
> consume SErrors. The RAS Extensions document (ARM DDI0587),
> '2.4.1 ESB and Unrecoverable errors' describes ESB as synchronising
> SError interrupts generated by 'instructions, translation table walks,
> hardware updates to the translation tables, and instruction fetches on
> the same PE'. This makes ESB equivalent to KVMs existing
> 'dsb, mrs-daifclr, isb' sequence.
> 
> Use the alternatives to synchronise and consume any SError using ESB
> instead of unmasking and taking the SError. Set ARM_EXIT_WITH_SERROR_BIT
> in the exit_code so that we can restart the vcpu if it turns out this
> SError has no impact on the vcpu.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v4:
>  * Moved the SError handling into handle_exit_early()
>  * Dropped Marc & Christoffer's Reviewed-by due to handle_exit_early().
> 

I realize this is queued, but for good measure, I'm still happy with
this change after handle_exit_early().

Thanks,
-Christoffer