Re: [PATCH 0/8] KVM: SEV-ES: fixes for string I/O emulation

Paolo Bonzini
2021-10-22T13:33:58Z

On 22/10/21 01:49, Sean Christopherson wrote:
> On Wed, Oct 13, 2021, Paolo Bonzini wrote:
>> Patches 2 to 7 are a bunch of cleanups to emulator_pio_in and
>> emulator_pio_in_out, so that the final SEV code is a little easier
>> to reason on. Just a little, no big promises.
> IMO, this series goes in the wrong direction and doesn't make the mess any better,
> just different.
>
> The underlying issue is that kernel_pio() does the completely horrendous thing
> of consuming vcpu->arch.pio. That leads to the juggling that this series tries
> to clean up, but it's essentially an impossible problem to solve because the
> approach itself is broken.

I agree on this, but I disagree that the series does not make the mess
any better. At the very least, the new signatures for
__emulator_pio_in, complete_emulator_pio_in and emulator_pio_in_out are
improvements regarding the _role_ of vcpu->arch.pio*:

- complete_emulator_pio_in clearly takes the values from vcpu->arch.pio,
which _is_ the right thing to do for a complete_userspace_io function.
This is not clear of emulator_pio_in before the patch

- __emulator_pio_in and emulator_pio_in_out do not take anymore the
buffer argument, making it clear that they operate on the internal
pio_data buffer and only complete_emulator_pio_in copies out of it.
Which yes is horrible, but at least it is clearly visible in the code now.

I managed to clean things up quite satisfactorily with just 6 patches on
top of these eight, so I'll post the full series as soon as I finish
testing them. 5.15 can then include these to fix the bug at hand.

Paolo