[v1] target/arm: Fix SCR_EL3 migration issue

[PATCH 0/1] target/arm: Fix SCR_EL3 migration issue

Posted by michael.nawrocki--- via 3 years, 3 months ago

The SCR_EL3 register reset value (0)  and the value produced when
writing 0 via the scr_write function (set as writefn in the register
struct) differ. This causes migration to fail.

I believe the solution is to specify a raw_writefn for that register.

Failing invocation:
$ qemu-system-arm -machine vexpress-a9 -cpu cortex-a9 -nographic
QEMU 5.2.0 monitor - type 'help' for more information
(qemu) migrate "exec:cat > img"
(qemu) q
$ qemu-system-arm -machine vexpress-a9 -cpu cortex-a9 -nographic -incoming "exec:cat img"
qemu-system-arm: error while loading state for instance 0x0 of device 'cpu'
qemu-system-arm: load of migration failed: Operation not permitted


Mike Nawrocki (1):
  target/arm: Add raw_writefn to SCR_EL3 register

 target/arm/helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.20.1

Re: [PATCH 0/1] target/arm: Fix SCR_EL3 migration issue

Posted by Peter Maydell 3 years, 3 months ago

On Thu, 28 Jan 2021 at 14:31, Mike Nawrocki
<michael.nawrocki@gtri.gatech.edu> wrote:
>
> The SCR_EL3 register reset value (0)  and the value produced when
> writing 0 via the scr_write function (set as writefn in the register
> struct) differ. This causes migration to fail.
>
> I believe the solution is to specify a raw_writefn for that register.
>
> Failing invocation:
> $ qemu-system-arm -machine vexpress-a9 -cpu cortex-a9 -nographic
> QEMU 5.2.0 monitor - type 'help' for more information
> (qemu) migrate "exec:cat > img"
> (qemu) q
> $ qemu-system-arm -machine vexpress-a9 -cpu cortex-a9 -nographic -incoming "exec:cat img"
> qemu-system-arm: error while loading state for instance 0x0 of device 'cpu'
> qemu-system-arm: load of migration failed: Operation not permitted

I'll review the patch later, but for the moment just a note that
I'm pretty sure this is not the only issue you'll run into with
trying to migrate an AArch32 TrustZone-enabled CPU.
https://bugs.launchpad.net/qemu/+bug/1839807 has the details
but in summary we aren't migrating the Secure banked contents
of cp15 registers which are banked Secure/Non-Secure. The
symptom will be that migration succeeds but the guest doesn't
behave correctly on the destination/after state restore.

thanks
-- PMM

Re: [PATCH 0/1] target/arm: Fix SCR_EL3 migration issue

Posted by Philippe Mathieu-Daudé 3 years, 2 months ago

Cc'ing avocado-devel for test idea.

On 1/28/21 3:31 PM, michael.nawrocki--- via wrote:
> The SCR_EL3 register reset value (0)  and the value produced when
> writing 0 via the scr_write function (set as writefn in the register
> struct) differ. This causes migration to fail.
> 
> I believe the solution is to specify a raw_writefn for that register.
> 
> Failing invocation:
> $ qemu-system-arm -machine vexpress-a9 -cpu cortex-a9 -nographic
> QEMU 5.2.0 monitor - type 'help' for more information
> (qemu) migrate "exec:cat > img"
> (qemu) q
> $ qemu-system-arm -machine vexpress-a9 -cpu cortex-a9 -nographic -incoming "exec:cat img"
> qemu-system-arm: error while loading state for instance 0x0 of device 'cpu'
> qemu-system-arm: load of migration failed: Operation not permitted
> 
> 
> Mike Nawrocki (1):
>   target/arm: Add raw_writefn to SCR_EL3 register
> 
>  target/arm/helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>