KVM: arm64: nv: Unfudge ID_AA64PFR0_EL1 masking

Marc reports that L1 VMs aren't booting with the NV series applied to
today's kvmarm/next. After bisecting the issue, it appears that
44241f34fac9 ("KVM: arm64: nv: Use accessors for modifying ID
registers") is to blame.

Poking around at the issue a bit further, it'd appear that the value for
ID_AA64PFR0_EL1 is complete garbage, as 'val' still contains the value
we set ID_AA64ISAR1_EL1 to.

Fix the read-modify-write pattern to actually use ID_AA64PFR0_EL1 as the
starting point. Excuse me as I return to my shame cube.

Reported-by: Marc Zyngier <maz@kernel.org>
Fixes: 44241f34fac9 ("KVM: arm64: nv: Use accessors for modifying ID registers")
Acked-by: Marc Zyngier <maz@kernel.org>
Tested-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240621224044.2465901-1-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 44085c13e673a1c7f50d8ca46dffa850405e4d4b..794ed18c05375fd1229273c4b26e2e03ef27c91d 100644 (file)
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -40,7 +40,7 @@ static void limit_nv_id_regs(struct kvm *kvm)
        kvm_set_vm_id_reg(kvm, SYS_ID_AA64ISAR1_EL1, val);
 
        /* No AMU, MPAM, S-EL2, RAS or SVE */
-       kvm_read_vm_id_reg(kvm, SYS_ID_AA64PFR0_EL1);
+       val = kvm_read_vm_id_reg(kvm, SYS_ID_AA64PFR0_EL1);
        val &= ~(GENMASK_ULL(55, 52)    |
                 NV_FTR(PFR0, AMU)      |
                 NV_FTR(PFR0, MPAM)     |