linux-kernel - Re: [PATCH 2/3] perf: arm_spe: Disable buffer before writing to PMBPTR_EL1 or PMBSR

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Message-ID: <aL7hvEXjXpoyDCQf@willie-the-truck>
Date: Mon, 8 Sep 2025 15:01:32 +0100
From: Will Deacon <will@...nel.org>
To: James Clark <james.clark@...aro.org>
Cc: Mark Rutland <mark.rutland@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Alexandru Elisei <Alexandru.Elisei@....com>,
	Anshuman Khandual <Anshuman.Khandual@....com>,
	Rob Herring <Rob.Herring@....com>,
	Suzuki Poulose <Suzuki.Poulose@....com>,
	Robin Murphy <Robin.Murphy@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	maz@...nel.org
Subject: Re: [PATCH 2/3] perf: arm_spe: Disable buffer before writing to
 PMBPTR_EL1 or PMBSR_EL1

On Tue, Jul 01, 2025 at 04:31:58PM +0100, James Clark wrote:
> DEN0154 states that writes to PMBPTR_EL1 or PMBSR_EL1 must be done while
> the buffer is disabled (PMBLIMITR_EL1.E == 0). Re-arrange the interrupt
> handler to always disable the buffer for non-spurious interrupts before
> doing either.

Why is DEN0154 not part of the Arm ARM?

Trying to tighten the programmers model retrospectively in a separate
spec is a lovely idea but I'm not hugely interested in it. The driver is
written to the text in the Arm ARM and is going to stay that way. Any
future changes in the architecture need to be backwards compatible.

If we have to poke the thing differently in a VM, we might as well use
hypercalls/PV.

Will