KVM: arm64/sve: Clean up UAPI register ID definitions

Currently, the SVE register ID macros are not all defined in the
same way, and advertise the fact that FFR maps onto the nonexistent
predicate register P16.  This is really just for kernel
convenience, and may lead userspace into bad habits.

Instead, this patch masks the ID macro arguments so that
architecturally invalid register numbers will not be passed through
any more, and uses a literal KVM_REG_ARM64_SVE_FFR_BASE macro to
define KVM_REG_ARM64_SVE_FFR(), similarly to the way the _ZREG()
and _PREG() macros are defined.

Rather than plugging in magic numbers for the number of Z- and P-
registers and the maximum possible number of register slices, this
patch provides definitions for those too.  Userspace is going to
need them in any case, and it makes sense for them to come from
<uapi/asm/kvm.h>.

sve_reg_to_region() uses convenience constants that are defined in
a different way, and also makes use of the fact that the FFR IDs
are really contiguous with the P15 IDs, so this patch retains the
existing convenience constants in guest.c, supplemented with a
couple of sanity checks to check for consistency with the UAPI
header.

Fixes: e1c9c98345b3 ("KVM: arm64/sve: Add SVE support to register access ioctl interface")
Suggested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 4f7b26bbf671..2e449e1dea73 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -325,6 +325,15 @@ static int sve_reg_to_region(struct sve_state_reg_region *region,
 
 	size_t sve_state_size;
 
+	const u64 last_preg_id = KVM_REG_ARM64_SVE_PREG(SVE_NUM_PREGS - 1,
+							SVE_NUM_SLICES - 1);
+
+	/* Verify that the P-regs and FFR really do have contiguous IDs: */
+	BUILD_BUG_ON(KVM_REG_ARM64_SVE_FFR(0) != last_preg_id + 1);
+
+	/* Verify that we match the UAPI header: */
+	BUILD_BUG_ON(SVE_NUM_SLICES != KVM_ARM64_SVE_MAX_SLICES);
+
 	/* Only the first slice ever exists, for now: */
 	if ((reg->id & SVE_REG_SLICE_MASK) != 0)
 		return -ENOENT;