Re: [PATCH] arm64: Run enable method for errata work arounds on late CPUs

From: Robin Murphy <robin.murphy@arm.com>
To: Dave Martin <Dave.Martin@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	catalin.marinas@arm.com, will.deacon@arm.com,
	linux-kernel@vger.kernel.org,
	Andre Przywara <andre.przywara@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: Run enable method for errata work arounds on late CPUs
Date: Wed, 17 Jan 2018 13:20:42 +0000	[thread overview]
Message-ID: <29147833-b47f-3ad9-e2d8-295551c43900@arm.com> (raw)
In-Reply-To: <20180117122548.GE22781@e103592.cambridge.arm.com>

On 17/01/18 12:25, Dave Martin wrote:
> On Wed, Jan 17, 2018 at 10:05:56AM +0000, Suzuki K Poulose wrote:
>> When a CPU is brought up after we have finalised the system
>> wide capabilities (i.e, features and errata), we make sure the
>> new CPU doesn't need a new errata work around which has not been
>> detected already. However we don't run enable() method on the new
>> CPU for the errata work arounds already detected. This could
>> cause the new CPU running without potential work arounds.
>> It is upto the "enable()" method to decide if this CPU should
>> do something about the errata.
>>
>> Fixes: commit 6a6efbb45b7d95c84 ("arm64: Verify CPU errata work arounds on hotplugged CPU")
>> Cc: Will Deacon <will.deacon@arm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Andre Przywara <andre.przywara@arm.com>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Dave Martin <dave.martin@arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>>   arch/arm64/kernel/cpu_errata.c | 9 ++++++---
>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
>> index 90a9e465339c..54e41dfe41f6 100644
>> --- a/arch/arm64/kernel/cpu_errata.c
>> +++ b/arch/arm64/kernel/cpu_errata.c
>> @@ -373,15 +373,18 @@ void verify_local_cpu_errata_workarounds(void)
>>   {
>>   	const struct arm64_cpu_capabilities *caps = arm64_errata;
>>   
>> -	for (; caps->matches; caps++)
>> -		if (!cpus_have_cap(caps->capability) &&
>> -			caps->matches(caps, SCOPE_LOCAL_CPU)) {
>> +	for (; caps->matches; caps++) {
>> +		if (cpus_have_cap(caps->capability)) {
>> +			if (caps->enable)
>> +				caps->enable((void *)caps);
> 
> Do we really need this cast?

Seems to me like the prototype for .enable needs updating. If any 
existing callback was actually using the (non-const) void* for some 
purpose (thankfully nothing seems to be), then passing the capability 
pointer into that would be unlikely to end well anyway.

We probably want to replace or append that with a proper const struct 
arm64_cpu_capabilities* argument, to make it more of a method call.

Robin.

> Can enable() fail, or do we already guarantee that it succeeds (by
> having detected the cap in the first place)?
> 
>> +		} else if (caps->matches(caps, SCOPE_LOCAL_CPU)) {
> 
> [...]
> 
> Cheers
> ---Dave
> 
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