[PATCH v6 15/64] KVM: arm64: nv: Handle HCR_EL2.E2H specially

Marc Zyngier
2022-01-28T12:33:02Z

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 <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
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 ace4a54caef9..102bc4906723 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -183,9 +183,24 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
goto memory_write;

if (unlikely(get_el2_to_el1_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
@@ -193,6 +208,11 @@ 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);