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Subject: Re: [PATCH v12 6/7] arm64: mte: Save/Restore TFSR_EL1 during suspend
To:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        kasan-dev@googlegroups.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Will Deacon <will@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Andrey Konovalov <andreyknvl@google.com>
References: <20210208165617.9977-1-vincenzo.frascino@arm.com>
 <20210208165617.9977-7-vincenzo.frascino@arm.com>
 <20210209115533.GE1435@arm.com>
 <20210209143328.GA27791@e121166-lin.cambridge.arm.com>
From:   Vincenzo Frascino <vincenzo.frascino@arm.com>
Message-ID: <2a551330-111b-4cb4-51d1-190f2c6d8493@arm.com>
Date:   Tue, 9 Feb 2021 14:54:13 +0000
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On 2/9/21 2:33 PM, Lorenzo Pieralisi wrote:
>> 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).
> 
> 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 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.
> 

Ok, based on what you are saying it seems that the most viable solution here is
to save and restore TFSR_EL1. I will update my code accordingly.

> Thanks,
> Lorenzo
> 

-- 
Regards,
Vincenzo