Re: [PATCH 1/2] arm64: Add support for FEAT_HAFT

[Marc Zyngier <maz@kernel.org>]

On Tue, 06 Aug 2024 04:09:09 +0100,
Yicong Yang <yangyicong@huawei.com> wrote:
> 
> >> +#ifdef CONFIG_ARM64_HAFT
> >> +	{
> >> +		.desc = "Hardware managed Access Flag for Table Descriptor",
> >> +		/*
> >> +		 * Per Spec, software management of Access Flag for Table
> >> +		 * descriptor is not supported, so make this feature system
> >> +		 * wide.
> >> +		 */
> > 
> > I don't understand what you mean by this. Can you please clarify?
> > 
> 
> Since this cannot be managed by the software, we should restrict all the CPUs
> in the system to have and enable this feature which is indicated by
> ARM64_CPUCAP_BOOT_CPU_FEATURE. It's not possible for part of the CPUs don't have
> this feature and managed manually.
> 
> I make this comment here since it's handled different from what ARM64_HW_DBM does (which
> is ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE). Maybe it's redundant and can be dropped.

Ah, I see what you mean. I think this is still important to capture,
but maybe in a clearer manner. Something like:

	Contrary to the page/block access flag, the table access flag
	cannot be emulated in software (no access fault will occur).
	Therefore mandate that all CPUs have FEAT_HAFT.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.