[PATCH] KVM: arm64: Flush HCR_EL2.VSE to deliver SErrors to pKVM guests

[tabba at google.com]

With pKVM enabled, the host injects a virtual SError by setting
HCR_EL2.VSE on its vCPU copy, but flush_hyp_vcpu() only flows TWI/TWE
into the hyp vCPU that runs, so VSE never reaches it and a deferred
(masked) SError is never delivered. VSE is a host-owned injection
control, not a trap-configuration bit, so restricting the host's
trap-register values should not have dropped it. Flow it on entry;
sync_hyp_vcpu() already copies hcr_el2 back, so delivery is reflected
to the host.

Fixes: b56680de9c648 ("KVM: arm64: Initialize trap register values in hyp in pKVM")
Reported-by: Sashiko (local):gemini-3.1-pro
Signed-off-by: Fuad Tabba <tabba at google.com>
---
Not an urgent fix. I should stop running Sashiko...
---
 arch/arm64/kvm/hyp/nvhe/hyp-main.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 06db299c37a8..9e4a20df6409 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -129,9 +129,14 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 	hyp_vcpu->vcpu.arch.ctxt	= host_vcpu->arch.ctxt;
 
 	hyp_vcpu->vcpu.arch.mdcr_el2	= host_vcpu->arch.mdcr_el2;
-	hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWI | HCR_TWE);
+	/*
+	 * HCR_EL2.VSE is host-owned (a pending virtual SError to inject), not a
+	 * trap-control bit, so it must flow to the hyp vCPU alongside TWI/TWE
+	 * for the vSError to be delivered. sync_hyp_vcpu() reflects it back.
+	 */
+	hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWI | HCR_TWE | HCR_VSE);
 	hyp_vcpu->vcpu.arch.hcr_el2 |= READ_ONCE(host_vcpu->arch.hcr_el2) &
-						 (HCR_TWI | HCR_TWE);
+						 (HCR_TWI | HCR_TWE | HCR_VSE);
 
 	hyp_vcpu->vcpu.arch.iflags	= host_vcpu->arch.iflags;
 
-- 
2.54.0.929.g9b7fa37559-goog