Re: [PATCH v7 03/12] KVM: arm64: PMU: Clear PM{C,I}NTEN{SET,CLR} and PMOVS{SET,CLR} on vCPU reset

[Raghavendra Rao Ananta]

On Thu, Oct 19, 2023 at 12:06 PM Oliver Upton <oliver.upton@xxxxxxxxx> wrote:
>
> Hi Raghu,
>
> Can you please make sure you include leading and trailing whitespace for
> your inline replies? The message gets extremely dense and is difficult
> to read.
>
> Also -- delete any unrelated context from your replies. If there's a
> localized conversation about a particular detail there's no reason to
> keep the entire thread in the body.
>
Sorry about that. I'll try to keep it clean.

> On Thu, Oct 19, 2023 at 11:46:22AM -0700, Raghavendra Rao Ananta wrote:
> > On Wed, Oct 18, 2023 at 2:16 PM Raghavendra Rao Ananta
> > <rananta@xxxxxxxxxx> wrote:
> > > I had a brief discussion about this with Oliver, and it looks like we
> > > might need a couple of additional changes for these register accesses:
> > > - For the userspace accesses, we have to implement explicit get_user
> > > and set_user callbacks that to filter out the unimplemented counters
> > > using kvm_pmu_valid_counter_mask().
> > Re-thinking the first case: Since these registers go through a reset
> > (reset_pmu_reg()) during initialization, where the valid counter mask
> > is applied, and since we are sanitizing the registers with the mask
> > before running the guest (below case), will implementing the
> > {get,set}_user() add any value, apart from just keeping userspace in
> > sync with every update of PMCR.N?
>
> KVM's sysreg emulation (as seen from userspace) fails to uphold the RES0
> bits of these registers. That's a bug.
>
Got it. Thanks for the confirmation. I'll implement these as originally planned.

Thank you.
Raghavendra

> --
> Thanks,
> Oliver