Re: [XEN PATCH] hvmloader: Fix reading ACPI PM1 CNT value

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Jun 30, 2020 at 06:09:13PM +0100, Anthony PERARD wrote:
> In order to get the CNT value from QEMU, we were supposed to read a
> word, according to the implementation in QEMU. But it has been lax and
> allowed to read a single byte. This has changed with commit
> 5d971f9e6725 ("memory: Revert "memory: accept mismatching sizes in
> memory_region_access_valid"") and result in hvmloader crashing on
> the BUG_ON.

This is a bug on the QEMU side, the ACPI spec states: "Accesses to PM1
control registers are accessed through byte and word accesses.".
That's on section 4.8.3.2.1 PM1 Control Registers of my copy of the
ACPI spec (6.2A).

> 
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

I'm fine with this if such bogus behavior has made it's way into a
release version of QEMU, but it needs to state it's a workaround for a
QEMU bug, not a bug in hvmloader.

IMO the QEMU change should be reverted.

Thanks, Roger.