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

[Sean Christopherson]

 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.

The _only_ reason vcpu->arch.pio (the structure) exists is to snapshot a port I/O
operation that didn't originate from the emulator before exiting to userspace,
i.e. "fast" I/O and now SEV-ES.  Ignoring those two, all info comes from the
emulator and a single flag or even the cui pointer would suffice.

Ditto for pio_data, it's purely needed to let userspace read/write values, its
use directly in any code except those specific paths is just bad code.

So instead of juggling vcpu->arch.pio.count in weird places, just don't set the
damn thing in the first place.

Untested patches attached that frame in where I think we should go with this.

I'll be offline until Monday, apologies for the inconvenience.