I don't profess to understand most of this, I am just a user who found
something didn't work and tracked down the cause with help from the
people on the bugtracker.
the min=1 and max=4 was chosen as it seems to be set that way in most
other places in the source, and 2 fits in that range.
so as macos seems to require 2 bytes but spec says 4 (32 bits) would it
be better to set min=2 max=4, given that the original revert seems to be
a security fix?
this works equally well:
static const MemoryRegionOps acpi_pm_tmr_ops = {
.read = acpi_pm_tmr_read,
.write = acpi_pm_tmr_write,
.valid.min_access_size = 2,
.valid.max_access_size = 4,
.endianness = DEVICE_LITTLE_ENDIAN,
};
regards.
On 13/07/2020 12:14, Michael S. Tsirkin wrote:
On Mon, Jul 13, 2020 at 10:20:12AM +0300, Michael Tokarev wrote:
12.07.2020 15:00, Simon John wrote:
macos guests no longer boot after commit
5d971f9e672507210e77d020d89e0e89165c8fc9
acpi-tmr needs 2 byte memory accesses, so breaks as that commit only allows 4
bytes.
Fixes: 5d971f9e672507210e7 (memory: Revert "memory: accept mismatching sizes in
memory_region_access_valid")
Buglink: https://bugs.launchpad.net/qemu/+bug/1886318
Actually this fixes 77d58b1e47c8d1c661f98f12b47ab519d3561488
Author: Gerd Hoffmann <kra...@redhat.com>
Date: Thu Nov 22 12:12:30 2012 +0100
Subject: apci: switch timer to memory api
Signed-off-by: Gerd Hoffmann <kra...@redhat.com>
because this is the commit which put min_access_size = 4 in there
(5d971f9e672507210e7 is just a messenger, actual error were here
earlier but it went unnoticed).
While min_access_size=4 was most likely an error, I wonder why
we use 1 now, while the subject says it needs 2? What real min
size is here for ACPI PM timer?
/mjt
Well the ACPI spec 1.0b says
4.7.3.3 Power Management Timer (PM_TMR)
...
This register is accessed as 32 bits.
and this text is still there in 6.2.
So it's probably worth it to cite this in the commit log
and explain it's a spec violation.
I think it's better to be restrictive and only allow the
minimal variation from spec - in this case I guess this means 2 byte
reads.
In any case pls do include an explanation for why you picked
one over the other.
Signed-off-by: Simon John <g...@the-jedi.co.uk>
---
 hw/acpi/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/hw/acpi/core.c b/hw/acpi/core.c
index f6d9ec4f13..05ff29b9d7 100644
--- a/hw/acpi/core.c
+++ b/hw/acpi/core.c
@@ -527,7 +527,7 @@ static void acpi_pm_tmr_write(void *opaque, hwaddr addr,
uint64_t val,
 static const MemoryRegionOps acpi_pm_tmr_ops = {
    .read = acpi_pm_tmr_read,
    .write = acpi_pm_tmr_write,
-Â Â Â .valid.min_access_size = 4,
+Â Â Â .valid.min_access_size = 1,
    .valid.max_access_size = 4,
    .endianness = DEVICE_LITTLE_ENDIAN,
 };
--
Simon John