Re: [PATCH v4 0/4] Enable writable for idregs DFR0,PFR0, MMFR{0,1,2}

From: Oliver Upton <oliver.upton@linux.dev>
To: Jing Zhang <jingzhangos@google.com>
Cc: KVM <kvm@vger.kernel.org>, KVMARM <kvmarm@lists.linux.dev>,
	ARMLinux <linux-arm-kernel@lists.infradead.org>,
	Marc Zyngier <maz@kernel.org>, Oliver Upton <oupton@google.com>,
	Will Deacon <will@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Fuad Tabba <tabba@google.com>, Reiji Watanabe <reijiw@google.com>,
	Raghavendra Rao Ananta <rananta@google.com>,
	Suraj Jitindar Singh <surajjs@amazon.com>
Subject: Re: [PATCH v4 0/4] Enable writable for idregs DFR0,PFR0, MMFR{0,1,2}
Date: Mon, 26 Jun 2023 20:52:46 +0000	[thread overview]
Message-ID: <ZJn6niA1RgAqu7DC@linux.dev> (raw)
In-Reply-To: <20230607194554.87359-1-jingzhangos@google.com>

Hi Jing,

On Wed, Jun 07, 2023 at 07:45:50PM +0000, Jing Zhang wrote:
> 
> This patch series enable userspace writable for below idregs:
> ID_AA64DFR0_EL1, ID_DFR0_EL1, ID_AA64PFR0_EL1, ID_AA64MMFR{0, 1, 2}_EL1.
> 
> It is based on below series [2] which add infrastructure for writable idregs.

Could you implement some tests for these changes? We really need to see
that userspace is only allowed to select a subset of features that're
provided by the host, and that the CPU feature set never exceeds what
the host can support.

Additionally, there are places in the kernel where we use host ID
register values for the sake of emulation (DBGDIDR, LORegion). These
both should instead be using the _guest_ ID register values.

-- 
Thanks,
Oliver

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