Subject: [PATCH v2 16/94] KVM: arm64: nv: Handle HCR_EL2.E2H specially

From: Marc Zyngier <[email-masked]>
Date: Tue, 11 Feb 2020 17:48:20 +0000

HCR_EL2.E2H is nasty, as a flip of this bit completely changes the way
we deal with a lot of the state. So when the guest flips this bit
(sysregs are live), do the put/load dance so that we have a consistent
state.

Yes, this is slow. Don't do it.

Suggested-by: Alexandru Elisei <[email-masked]>
Signed-off-by: Marc Zyngier <[email-masked]>
---
 arch/arm64/kvm/sys_regs.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 8c7d3d410689..9b29ac37829b 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -308,9 +308,24 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
 		goto memory_write;
 
 	if (unlikely(get_el2_mapping(reg, &el1r, &xlate))) {
+		bool need_put_load;
+
 		if (!is_hyp_ctxt(vcpu))
 			goto memory_write;
 
+		/*
+		 * HCR_EL2.E2H is nasty: it changes the way we interpret a
+		 * lot of the EL2 state, so treat is as a full state
+		 * transition.
+		 */
+		need_put_load = ((reg == HCR_EL2) &&
+				 vcpu_el2_e2h_is_set(vcpu) != !!(val & HCR_E2H));
+
+		if (need_put_load) {
+			preempt_disable();
+			kvm_arch_vcpu_put(vcpu);
+		}
+
 		/*
 		 * Always store a copy of the write to memory to avoid having
 		 * to reverse-translate virtual EL2 system registers for a
@@ -318,6 +333,11 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
 		 */
 		__vcpu_sys_reg(vcpu, reg) = val;
 
+		if (need_put_load) {
+			kvm_arch_vcpu_load(vcpu, smp_processor_id());
+			preempt_enable();
+		}
+
 		switch (reg) {
 		case ELR_EL2:
 			write_sysreg_el1(val, SYS_ELR);
-- 
2.20.1

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