Re: [PATCH v12 15/39] KVM: arm64: Manage GCS access and registers for guests

From: Marc Zyngier <maz@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Mark Brown <broonie@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Arnd Bergmann <arnd@arndb.de>, Oleg Nesterov <oleg@redhat.com>,
	Eric Biederman <ebiederm@xmission.com>,
	Shuah Khan <shuah@kernel.org>,
	"Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
	Deepak Gupta <debug@rivosinc.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
	Kees Cook <kees@kernel.org>, "H.J. Lu" <hjl.tools@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Florian Weimer <fweimer@redhat.com>,
	Christian Brauner <brauner@kernel.org>,
	Thiago Jung Bauermann <thiago.bauermann@linaro.org>,
	Ross Burton <ross.burton@arm.com>,
	Yury Khrustalev <yury.khrustalev@arm.com>,
	Wilco Dijkstra <wilco.dijkstra@arm.com>,
	linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
	kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-mm@kvack.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v12 15/39] KVM: arm64: Manage GCS access and registers for guests
Date: Tue, 03 Sep 2024 17:24:24 +0100	[thread overview]
Message-ID: <86r0a0vh6v.wl-maz@kernel.org> (raw)
In-Reply-To: <20240829-arm64-gcs-v12-15-42fec947436a@kernel.org>

On Thu, 29 Aug 2024 00:27:31 +0100,
Mark Brown <broonie@kernel.org> wrote:
> 
> GCS introduces a number of system registers for EL1 and EL0, on systems
> with GCS we need to context switch them and expose them to VMMs to allow
> guests to use GCS.
> 
> In order to allow guests to use GCS we also need to configure
> HCRX_EL2.GCSEn, if this is not set GCS instructions will be noops and
> CHKFEAT will report GCS as disabled.  Also enable fine grained traps for
> access to the GCS registers by guests which do not have the feature
> enabled.
> 
> In order to allow userspace to control availability of the feature to
> guests we enable writability for only ID_AA64PFR1_EL1.GCS, this is a
> deliberately conservative choice to avoid errors due to oversights.
> Further fields should be made writable in future.
> 
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
>  arch/arm64/include/asm/kvm_host.h          | 12 ++++++++
>  arch/arm64/include/asm/vncr_mapping.h      |  2 ++
>  arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 49 ++++++++++++++++++++++++------
>  arch/arm64/kvm/sys_regs.c                  | 27 +++++++++++++++-
>  4 files changed, 79 insertions(+), 11 deletions(-)

FWIW, this patch is going to conflict badly with -next, because of the
"conservative" approach to dealing with ID_AA64PFR1_EL1 (thankfully,
the *progressive* approach has been merged).

If it gets stuck on a branch together with patch #11 (which seems to
be the minimum for things to compile), I can take it independently and
fix it myself. Just let me know.

Thanks,

	M.

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