Subject: Re: [RFC PATCH 1/1] KVM: PPC: Report single stepping capability

From: Fabiano Rosas <[email-masked]>
Date: Thu, 21 Mar 2019 11:35:54 -0300

Alexey Kardashevskiy <[email-masked]> writes:

> In the cover letter (which is not really required for a single patch)
> you say the capability will be present for BookE and PR KVM (which
> Book3s) but here it is BookE only, is that intentional?

A few lines below (falling through) we have:

        /* We support this only for PR */
        r = !hv_enabled;

> Also, you need to update Documentation/virtual/kvm/api.txt for the new
> capability. After reading which I started wondering could not we just
> use existing KVM_CAP_GUEST_DEBUG_HW_BPS?

We _could_, but I think that would conflate two different
concepts. Single stepping does not necessarily makes use of hardware
breakpoints (e.g. Trace Interrupt on Book3s PR).

I also think we should use KVM_CAP_GUEST_DEBUG_HW_BPS in the future to
let QEMU know about: i) the lack of hardware breakpoints in Book3s and
ii) BookE's hardware breakpoints (Instruction Address Compare) that are
currently not being reported via HW_BPS.