linux-kernel - Re: [PATCH v2 5/6] KVM: arm64: show writable masks for feature registers

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Date: Wed, 1 May 2024 07:31:35 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Sebastian Ott <sebott@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH v2 5/6] KVM: arm64: show writable masks for feature
 registers

On Fri, Apr 26, 2024 at 12:49:49PM +0200, Sebastian Ott wrote:
> Instead of using ~0UL provide the actual writable mask for
> non-id feature registers in the output of the
> KVM_ARM_GET_REG_WRITABLE_MASKS ioctl.

Urgh, yeah in retrospect I think we should've constrained this to the
registers KVM considers "id regs" (the space occupied by known registers
or otherwise RAZ).

> Explicitely set the mask for CLIDR_EL1 to make sure we present
> the same value to userspace than before.

typo: explicitly

Also, we know the set of mutable bits for CLIDR_EL1 as it is handled in
set_clidr(). The mask really should match that, since the UAPI is
documented as "allowing userspace to know what fields can be changed for
the system register"

-- 
Thanks,
Oliver