Re: [PATCH v4 1/6] KVM: arm64: Correctly treat writes to OSLSR_EL1 as undefined

On Wed, Dec 15, 2021 at 01:09:28PM +0000, Oliver Upton wrote:

Hi Mark,

On Wed, Dec 15, 2021 at 11:39:58AM +0000, Mark Rutland wrote:

quoted

Hi Oliver,

On Tue, Dec 14, 2021 at 05:28:07PM +0000, Oliver Upton wrote:

quoted

Any valid implementation of the architecture should generate an
undefined exception for writes to a read-only register, such as
OSLSR_EL1. Nonetheless, the KVM handler actually implements write-ignore
behavior.

Align the trap handler for OSLSR_EL1 with hardware behavior. If such a
write ever traps to EL2, inject an undef into the guest and print a
warning.

I think this can still be read amibguously, since we don't explicitly state
that writes to OSLSR_EL1 should never trap (and the implications of being
UNDEFINED are subtle). How about:

| Writes to OSLSR_EL1 are UNDEFINED and should never trap from EL1 to EL2, but
| the KVM trap handler for OSLSR_EL1 handlees writes via ignore_write(). This

Whoops, with s/handlees/handles/

quoted

| is confusing to readers of the code, but shouldn't have any functional impact.
|
| For clarity, use write_to_read_only() rather than ignore_write(). If a trap
| is unexpectedly taken to EL2 in violation of the architecture, this will
| WARN_ONCE() and inject an undef into the guest.

Agreed, I like your suggested changelog better :-)

Cool!

Mark.

quoted

With that:

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Thanks!

--
Best,
Oliver

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