[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

  • To: Anthony PERARD <anthony.perard@xxxxxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Wed, 1 Jul 2020 09:52:57 +0200
  • Authentication-results: esa6.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Delivery-date: Wed, 01 Jul 2020 07:53:28 +0000
  • Ironport-sdr: fu4Ta5yH48MNwr0gP2MVL6yw9LSfyA5rlJq8yvKUM8DgJerDobGFXP5s5Y5Vowq8bH1xZ895ok TNKWZvURzOpr2Db5nmRC+iie24wL0URnYhjvZ3GZfsBsTEea/XZH3fcDLlhJd0K3JlkdQHAsJm wax/R2cohQpN7wNZzhkPU4y/UpX27bhjAFxwWq7JOeZeKdQwae+VnCPQxvvGKX2nnoL/klr22b URHOhlRPdbmYDESKpUS0b/a17KI+LklSqE9swgF/wM4pzuXyCZWZvOS0Mu+zN9YkWede3EmEKu srI=
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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 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.



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.