Re: [PATCH v1 3/8] KVM: arm64: Enable LS64 instructions when supported by guest

[Marc Zyngier <maz@kernel.org>]

On Tue, 04 Nov 2025 12:59:01 +0000,
Fuad Tabba <tabba@google.com> wrote:
> 
> The FEAT_LS64* family (FEAT_LS64, FEAT_LS64_V, FEAT_LS64_ACCDATA)
> enables support for LD64B, ST64B, and their variants. If a guest is
> advertised these features, KVM should not trap accesses to these
> instructions to EL2.
> 
> This is controlled by the HCRX_EL2_EnASR, HCRX_EL2_EnALS, and
> HCRX_EL2_EnAS0 bits. When clear, these bits trap the corresponding
> instructions. KVM did not set them, which would cause guest-supported
> instructions to trap.
> 
> This also created a state mismatch for nested virtualization, which
> validates its own HCRX_EL2 value against the features advertised in the
> guest's ID_AA64ISAR1_EL1 (in handle_other()).
> 
> Fix this by checking for each FEAT_LS64* variant in
> vcpu_set_hcrx() and setting the corresponding HCRX_EL2 enable
> bit if the guest supports the feature.
> 
> Signed-off-by: Fuad Tabba <tabba@google.com>

Please see 20240815125959.2097734-1-maz@kernel.org, which has a large
portion of what is required for this to work. Just flipping the bits
isn't quite enough.

Thanks,

	M.

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