Re: [PATCH 5/7] KVM: arm64: guest debug, add support for single-step

On 30 November 2014 at 10:10, Christoffer Dall
[off-list ref] wrote:

In any case, I think it was related to how userspace observes the state
of the CPU, because when you do the MMIO operation emulation in
userspace, currently if you observe the PC though GET_ONE_REG, you'll
see a PC pointing to the next instruction, not the one you're emulating
which is strange.

Also if we ever add support for userspace to say "this MMIO should
fault" then we definitely need the PC-advance to happen afterwards,
not before.

Not sure what the relation to a guest single-stepping itself was.

I think it just came up in the course of that discussion, because
single-step handling also needs to perform an action (clear PSTATE.SS)
as part of the "advance over this insn" operation. But I think that
you're right that doing the advance before dropping out to userspace
is no worse for singlestep than it is for any other case.

-- PMM