On Tue, Feb 09, 2021 at 02:33:28PM +0000, Lorenzo Pieralisi wrote:

On Tue, Feb 09, 2021 at 11:55:33AM +0000, Catalin Marinas wrote:

quoted

On Mon, Feb 08, 2021 at 04:56:16PM +0000, Vincenzo Frascino wrote:

quoted

When MTE async mode is enabled TFSR_EL1 contains the accumulative
asynchronous tag check faults for EL1 and EL0.

During the suspend/resume operations the firmware might perform some
operations that could change the state of the register resulting in
a spurious tag check fault report.

Save/restore the state of the TFSR_EL1 register during the
suspend/resume operations to prevent this to happen.

Do we need a similar fix for TFSRE0_EL1? We get away with this if
suspend is only entered on the idle (kernel) thread but I recall we
could also enter suspend on behalf of a user process (I may be wrong
though).

Yes, when we suspend the machine to RAM, we execute suspend on behalf
on a userspace process (but that's only running on 1 cpu, the others
are hotplugged out).

IIUC (and that's an if) TFSRE0_EL1 is checked on kernel entry so I don't
think there is a need to save/restore it (just reset it on suspend
exit).

You are right, we don't check TFSRE0_EL1 on return to user, only
clear it, so no need to do anything on suspend/resume.

TFSR_EL1, I don't see a point in saving/restoring it (it is a bit
per-CPU AFAICS) either, IMO we should "check" it on suspend (if it is
possible in that context) and reset it on resume.

I think this should work.

I don't think though you can "check" with IRQs disabled so I suspect
that TFSR_EL1 has to be saved/restored (which means that there is a
black out period where we run kernel code without being able to detect
faults but there is no solution to that other than delaying saving the
value to just before calling into PSCI). Likewise on resume from low
power.

It depends on whether kasan_report can be called with IRQs disabled. I
don't see why not, so if this works I'd rather just call mte_check_async
(or whatever it's called) on the suspend path and zero the register on
resume (mte_suspend_exit). We avoid any saving of the state.

-- 
Catalin

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