KVM: arm64: nv: Fix ATS12 handling of single-stage translation

Volodymyr reports that using a Xen DomU as a nested guest (where
HCR_EL2.E2H == 0), ATS12 results in a translation that stops at
the L2's S1, which isn't something you'd normally expects.

Comparing the code against the spec proves to be illuminating,
and suggests that the author of such code must have been tired,
cross-eyed, drunk, or maybe all of the above.

The gist of it is that, apart from HCR_EL2.VM or HCR_EL2.DC being
0, only the use of the EL2&0 translation regime limits the walk
to S1 only, and that we must finish the S2 walk in any other case.
Which solves the above issue, as E2H==0 indicates that ATS12 walks
the EL1&0 translation regime.

Explicitly checking for EL2&0 fixes this.

Reported-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Suggested-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Fixes: be04cebf3e788 ("KVM: arm64: nv: Add emulation of AT S12E{0,1}{R,W}")
Link: https://lore.kernel.org/r/20250806141707.3479194-2-volodymyr_babchuk@epam.com
Link: https://lore.kernel.org/r/20250809144811.2314038-2-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

0 files changed, 0 insertions, 0 deletions