Re: [RFC PATCH] KVM: arm64: don't single-step for non-emulated faults

[Peter Maydell]

On 9 November 2018 at 12:49, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> I'm not saying anything about *decisions*. I'm saying that we can make
> the state consistent by advancing the singlestep state in the same way
> that HW does, at the instant it advances the PC.
>
> i.e. do that in kvm_skip_instr(), as I've done in my local tree.
>
> That mirrors the HW, and we don't need to special-case any handling for
> emulated vs non-emulated instructions.

You also need to do it in the "set PC because we're making the guest
take an exception" code path, which doesn't go through kvm_skip_instr().
This corresponds to the two kinds of "step completed" in hardware as
noted in DDI0487D.a D2.12.3 fig D2-3 footnote b:
 * executing the instruction to be stepped without taking an exception
 * taking an exception to an exception level that debug exceptions
   are enabled from [ie guest EL1 in our case]

thanks
-- PMM