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

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

On Thu, 29 Aug 2024 00:27:31 +0100,
Mark Brown <broonie@...nel.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@...aro.org>
> Signed-off-by: Mark Brown <broonie@...nel.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.