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From: Suzuki K Poulose <>
To: Mark Brown <>,
	dann frazier <>
Cc: Catalin Marinas <>,
	Will Deacon <>,
Subject: Re: [PATCH] arm64: Generate cpucaps.h
Date: Tue, 21 Sep 2021 22:09:12 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 21/09/2021 19:35, Mark Brown wrote:
> On Tue, Sep 21, 2021 at 12:08:11PM -0600, dann frazier wrote:
>> On Wed, Apr 28, 2021 at 01:12:31PM +0100, Mark Brown wrote:
>>> This will result in a renumbering and reordering of the existing constants,
>>> since they are all internal only the values should not be important. The
>>> reordering will impact the order in which some steps in enumeration handle
>>> features but the algorithm is not intended to depend on this and I haven't
>>> seen any issues when testing.
>> Unfortunately I believe I've hit a regression[*] due to such an
>> ordering dependency. UNMAP_KERNEL_AT_EL0 currently needs to be
>> processed after WORKAROUND_CAVIUM_27456. ThunderX systems are
>> incompatible with KPTI, so unmap_kernel_at_el0() bails if
>> WORKAROUND_CAVIUM_27456 is set. Because of the sorting,
>> WORKAROUND_CAVIUM_27456 will not yet have been considered when
>> unmap_kernel_at_el0() checks for it, so the kernel tries to
>> run w/ KPTI - and quickly falls over.
>> I've verified that reordering cpucaps to move WORKAROUND_CAVIUM_27456
>> just above UNMAP_KERNEL_AT_EL0 restores the old behavior. I'm not sure
>> of the right way to address this - perhaps unmap_kernel_at_el0() could
>> check cavium_erratum_27456_cpus[] directly instead of keying on the

Given that these capabilities are LOCAL_CPU scope, and the systems in
question never have heterogeneous CPUs, you could replace

  cpus_have_const_cap() =>  this_cpu_has_cap()

in unmap_kernel_at_el0().

If they were heterogeneous, we would fail anyway, no matter what the
order was.


linux-arm-kernel mailing list

  reply	other threads:[~2021-09-21 21:11 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-28 12:12 [PATCH] arm64: Generate cpucaps.h Mark Brown
2021-04-29 12:32 ` Catalin Marinas
2021-05-04 11:43 ` Mark Rutland
2021-05-10 12:55 ` Catalin Marinas
2021-05-13  5:05 ` Anshuman Khandual
2021-05-13 11:51   ` Mark Rutland
2021-05-13 12:45   ` Mark Brown
2021-05-13 11:30 ` Geert Uytterhoeven
2021-05-13 13:03   ` Mark Brown
2021-09-21 18:08 ` dann frazier
2021-09-21 18:35   ` Mark Brown
2021-09-21 21:09     ` Suzuki K Poulose [this message]
2021-09-22 13:45       ` dann frazier

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