linux-kernel - Re: [PATCH v11 20/39] arm64/gcs: Context switch GCS state for EL0

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Message-ID: <ZsdkGJb93LjLUyzo@arm.com>
Date: Thu, 22 Aug 2024 17:15:20 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Mark Brown <broonie@...nel.org>
Cc: Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marc Zyngier <maz@...nel.org>,
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	Suzuki K Poulose <suzuki.poulose@....com>,
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	Eric Biederman <ebiederm@...ssion.com>,
	Shuah Khan <shuah@...nel.org>,
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	Deepak Gupta <debug@...osinc.com>, Ard Biesheuvel <ardb@...nel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@....com>, Kees Cook <kees@...nel.org>,
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Subject: Re: [PATCH v11 20/39] arm64/gcs: Context switch GCS state for EL0

On Thu, Aug 22, 2024 at 02:15:23AM +0100, Mark Brown wrote:
> There are two registers controlling the GCS state of EL0, GCSPR_EL0 which
> is the current GCS pointer and GCSCRE0_EL1 which has enable bits for the
> specific GCS functionality enabled for EL0. Manage these on context switch
> and process lifetime events, GCS is reset on exec().  Also ensure that
> any changes to the GCS memory are visible to other PEs and that changes
> from other PEs are visible on this one by issuing a GCSB DSYNC when
> moving to or from a thread with GCS.
> 
> Since the current GCS configuration of a thread will be visible to
> userspace we store the configuration in the format used with userspace
> and provide a helper which configures the system register as needed.
> 
> On systems that support GCS we always allow access to GCSPR_EL0, this
> facilitates reporting of GCS faults if userspace implements disabling of
> GCS on error - the GCS can still be discovered and examined even if GCS
> has been disabled.
> 
> Signed-off-by: Mark Brown <broonie@...nel.org>

We could do with a bit more code comments around GCSB DSYNC but
otherwise it looks fine now.

Reviewed-by: Catalin Marinas <catalin.marinas@....com>