linux-kernel - Re: [PATCH v5 1/3] selftests/lam: Move cpu_has

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Message-ID: <050c2ead-6261-4c46-8246-50c587eab227@intel.com>
Date: Fri, 24 Jan 2025 12:24:25 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
Cc: shuah@...nel.org, hpa@...or.com, x86@...nel.org,
 dave.hansen@...ux.intel.com, bp@...en8.de, mingo@...hat.com,
 tglx@...utronix.de, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, kirill@...temov.name,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v5 1/3] selftests/lam: Move cpu_has_la57() to use cpuinfo
 flag

On 1/24/25 12:17, Maciej Wieczor-Retman wrote:
>> Could you poke around and see if there is any existing ABI that we can
>> use to query LA57 support? Maybe one of the things KVM exports, or some
>> TASK_SIZE_MAX comparisons?
> Sure, I'll try to find some other way.
> 
> My previous tactic was to munmap() a high address and see if it works. Does that
> sound okay in case there isn't anything else would indicate la57 to userspace
> reliably?

Yeah, I think that's fine. I can't think of any obvious horrible
pitfalls. All I'd ask is that you spend 20 minutes grepping for things
that are conditional on X86_FEATURE_LA57 and see if there's anything
else that's a good candidate.