Re: [PATCH v2 6/6] selftests: KVM: Test OS lock behavior

On Tue, Nov 2, 2021 at 7:53 AM Oliver Upton [off-list ref] wrote:

quoted

I haven't had a change to properly review the series, but this one
definitely caught my eye. My expectations are that BRK is *not*
affected by the OS Lock. The ARMv8 ARM goes as far as saying:

<quote>
Breakpoint Instruction exceptions are enabled regardless of the state
of the OS Lock and the OS Double Lock.
</quote>

as well as:

<quote>
There is no enable control for Breakpoint Instruction exceptions. They
are always enabled, and cannot be masked.
</quote>

/facepalm I had thought I read "Breakpoint Instruction exceptions" in
the list on D2.5 "The effect of powerdown on debug exceptions",
although on second read I most definitely did not. And if I had read
the bottom of the section, I'd of seen one of the quotes.

quoted

I wonder how your test succeeds, though.

Probably because the expectations I wrote match the non-architected
behavior I implemented :-)

Alright, gave the series a good once over after this and fixed up
quite a few things. Unless you're ready for it, I'll hold back for a
bit to avoid spamming inboxes. As an FYI, here's the fixes I have
queued up:

v2 -> v3:
- Stop trapping debug exceptions when the OS Lock is enabled, as it
   does *not* block software breakpoint exceptions (Marc)
 - Trap accesses to debug registers if the OS Lock is enabled to prevent
   the guest from wiping out KVM's configuration of MDSCR_EL1
 - Update the debug-exceptions test to expect a software breakpoint
   exception even when the OS Lock is enabled.

--
Thanks,
Oliver

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