[PATCH] KVM: arm64: nv: Exclude guest's TWED configuration when TWE isn't set

[Oliver Upton <oliver.upton@linux.dev>]

KVM blindly OR's the guest values for TWEDEL and TWEDEn into the
programmed value even if the guest has WFE traps disabled. Exclude these
fields from the final value when TWE isn't set to avoid potentially
delaying a trap desired by the host.

Note that KVM doesn't use FEAT_TWED currently so there's no need to
empty out these fields the other way around (i.e. host TWE=0, guest
TWE=1).

Fixes: 04ab519bb86d ("KVM: arm64: nv: Configure HCR_EL2 for FEAT_NV2")
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/vhe/switch.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index 0998ad4a2552..e4955b49c0d2 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -95,6 +95,13 @@ static u64 __compute_hcr(struct kvm_vcpu *vcpu)
 			/* Force NV2 in case the guest is forgetful... */
 			guest_hcr |= HCR_NV2;
 		}
+
+		/*
+		 * Exclude the guest's TWED configuration if it hasn't set TWE
+		 * to avoid potentially delaying traps for the host.
+		 */
+		if (!(guest_hcr & HCR_TWE))
+			guest_hcr &= (HCR_EL2_TWEDEn | HCR_EL2_TWEDEL);
 	}
 
 	BUG_ON(host_data_test_flag(VCPU_IN_HYP_CONTEXT) &&

base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
-- 
2.39.5