Re: [PATCH 4/8] KVM: SEV-ES: clean up kvm_sev_es_ins/outs

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On 22/10/21 01:14, Maxim Levitsky wrote:
vcpu->arch.pio.count = 0;
^^^
I wonder what the rules are for clearing vcpu->arch.pio.count for userspace PIO vm exits.
Looks like complete_fast_pio_out clears it, but otherwise the only other place
that clears it in this case is x86_emulate_instruction when it restarts the instuction.
Do I miss something?

For IN, it is cleared by the completion callback.

For OUT, it can be cleared either by the completion callback or before calling it, because the completion callback will not need it. I would like to standardize towards clearing it in the callback for out, too, even if sometimes it's unnecessary to have a callback in the first place; this is what patch 8 does for example. This way vcpu->arch.pio.count > 0 tells you whether the other fields have a recent value.

Paolo




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