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

[Marc Zyngier]

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