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

Maxim Levitsky
2021-10-21T23:14:22Z

On Wed, 2021-10-13 at 12:56 -0400, Paolo Bonzini wrote:
> Remove the data argument and pull setting vcpu->arch.sev_pio_data into
> the caller; remove unnecessary clearing of vcpu->arch.pio.count when
> emulation is done by the kernel.

You forgot to mention that you inlined the call to emulator_pio_out_emulated/emulator_pio_in_emulated.

>
> No functional change intended.
>
> Cc: stable@vger.kernel.org
> Fixes: 7ed9abfe8e9f ("KVM: SVM: Support string IO operations for an SEV-ES guest")
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/x86.c | 31 +++++++++++++++----------------
> 1 file changed, 15 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 218877e297e5..8880dc36a2b4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12382,34 +12382,32 @@ static int complete_sev_es_emulated_ins(struct kvm_vcpu *vcpu)
> }
>
> static int kvm_sev_es_outs(struct kvm_vcpu *vcpu, unsigned int size,
> - unsigned int port, void *data, unsigned int count)
> + unsigned int port, unsigned int count)
> {
> - int ret;
> + int ret = emulator_pio_out(vcpu, size, port,
> + vcpu->arch.sev_pio_data, count);
>
> - ret = emulator_pio_out_emulated(vcpu->arch.emulate_ctxt, size, port,
> - data, count);
> - if (ret)
> + if (ret) {
> + /* Emulation done by the kernel. */
^^ This is a very good comment to have here!
> return ret;
> + }
>
> 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?

> -
> return 0;
> }
>
> static int kvm_sev_es_ins(struct kvm_vcpu *vcpu, unsigned int size,
> - unsigned int port, void *data, unsigned int count)
> + unsigned int port, unsigned int count)
> {
> - int ret;
> + int ret = emulator_pio_in(vcpu, size, port,
> + vcpu->arch.sev_pio_data, count);
>
> - ret = emulator_pio_in_emulated(vcpu->arch.emulate_ctxt, size, port,
> - data, count);
> if (ret) {
> - vcpu->arch.pio.count = 0;
> - } else {
> - vcpu->arch.sev_pio_data = data;
> - vcpu->arch.complete_userspace_io = complete_sev_es_emulated_ins;
> + /* Emulation done by the kernel. */
> + return ret;
> }
>
> + vcpu->arch.complete_userspace_io = complete_sev_es_emulated_ins;
> return 0;
> }
>
> @@ -12417,8 +12415,9 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
> unsigned int port, void *data, unsigned int count,
> int in)
> {
> - return in ? kvm_sev_es_ins(vcpu, size, port, data, count)
> - : kvm_sev_es_outs(vcpu, size, port, data, count);
> + vcpu->arch.sev_pio_data = data;
> + return in ? kvm_sev_es_ins(vcpu, size, port, count)
> + : kvm_sev_es_outs(vcpu, size, port, count);
> }
> EXPORT_SYMBOL_GPL(kvm_sev_es_string_io);
>

Looks OK to me, I might have missed something though.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky