Re: [PATCH 0/2] [Backport for 4.4.y stable] arm64 CTR_EL0 cpufeature fixes

[Sasha Levin <sashal@kernel.org>]

On Wed, Aug 07, 2019 at 11:59:41AM +0100, Suzuki K Poulose wrote:
>Hi Will,
>
>On 07/08/2019 10:49, Will Deacon wrote:
>>Hi Sasha, [+Suzuki]
>>
>>On Tue, Aug 06, 2019 at 05:29:04PM -0400, Sasha Levin wrote:
>>>On Mon, Aug 05, 2019 at 06:13:06PM +0100, Will Deacon wrote:
>>>>These two patches are backports for 4.4.y stable kernels after one of
>>>>them failed to apply:
>>>>
>>>>  https://lkml.kernel.org/r/156498316752100@kroah.com
>>>
>>>I took these 2, but note that they have two fixes that are not in 4.4:
>>>
>>>314d53d297980 arm64: Handle mismatched cache type
>>>4c4a39dd5fe2d arm64: Fix mismatched cache line size detection
>>>
>>>Will you send a backport for them?
>>
>>4.4 doesn't handle mismatches for the cache type or the line sizes, and
>>instead taints the kernel with a big splat at boot. If we wanted to
>>backport this, we'd need to pick up more than just the above patches, since
>>we don't have the means to emulate user cache maintenance operations either.
>>
>>Given that the vast majority of systems don't suffer from this problem,
>>I'd be inclined not to try shoe-horning all of this into 4.4, where I think
>>it's more likely introduce other issues.
>>
>>Suzuki, what do you think?
>
>I agree. It involves a lot of new code, with non-trivial backports.

Okay, makes sense. Thanks for looking into it.

--
Thanks,
Sasha