[RFC PATCH 26/26] kvm: arm64: Fix EL2 mode availability checks

[David Brazdil]

With nVHE hyp code interception host's PSCI CPU_ON/OFF/SUSPEND SMCs,
from the host's perspective new CPUs start booting in EL1 while
previously they would have booted in EL2. The kernel logic which keeps
track of the mode CPUs were booted in needs to be adjusted to account
for this fact.

Add a static key enabled if KVM nVHE initialization is successful.

When the key is enabled, is_hyp_mode_available continues to report
`true` because its users either treat it a check whether KVM will be /
has been initialized, or whether stub HVCs can be made (eg. hibernate).

is_hyp_mode_mismatched is changed to report `false` when the key is
enabled. That's because all cores' modes matched at the point of KVM
init and KVM will not allow cores not present at init to boot. That
said, the function is never used after KVM is initialized.

Signed-off-by: David Brazdil <dbrazdil at google.com>
---
 arch/arm64/include/asm/virt.h | 16 ++++++++++++++++
 arch/arm64/kvm/arm.c          |  5 +++++
 2 files changed, 21 insertions(+)

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 6069be50baf9..597430b5f5aa 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -65,9 +65,18 @@ extern u32 __boot_cpu_mode[2];
 void __hyp_set_vectors(phys_addr_t phys_vector_base);
 void __hyp_reset_vectors(void);
 
+DECLARE_STATIC_KEY_FALSE(kvm_nvhe_initialized);
+
 /* Reports the availability of HYP mode */
 static inline bool is_hyp_mode_available(void)
 {
+	/*
+	 * If KVM nVHE is initialized, all CPUs must have been booted in EL2.
+	 * Avoid checking __boot_cpu_mode as CPUs now come up in EL1.
+	 */
+	if (IS_ENABLED(CONFIG_KVM) && static_branch_unlikely(&kvm_nvhe_initialized))
+		return true;
+
 	return (__boot_cpu_mode[0] == BOOT_CPU_MODE_EL2 &&
 		__boot_cpu_mode[1] == BOOT_CPU_MODE_EL2);
 }
@@ -75,6 +84,13 @@ static inline bool is_hyp_mode_available(void)
 /* Check if the bootloader has booted CPUs in different modes */
 static inline bool is_hyp_mode_mismatched(void)
 {
+	/*
+	 * If KVM nVHE is initialized, all CPUs must have been booted in EL2.
+	 * Avoid checking __boot_cpu_mode as CPUs now come up in EL1.
+	 */
+	if (IS_ENABLED(CONFIG_KVM) && static_branch_unlikely(&kvm_nvhe_initialized))
+		return false;
+
 	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
 }
 
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 3dff6af69eca..e93956d6235d 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -47,6 +47,8 @@
 __asm__(".arch_extension	virt");
 #endif
 
+DEFINE_STATIC_KEY_FALSE(kvm_nvhe_initialized);
+
 DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
 
 static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
@@ -1841,6 +1843,9 @@ int kvm_arch_init(void *opaque)
 	if (err)
 		goto out_hyp;
 
+	if (!in_hyp_mode)
+		static_branch_enable(&kvm_nvhe_initialized);
+
 	if (in_hyp_mode)
 		kvm_info("VHE mode initialized successfully\n");
 	else
-- 
2.29.1.341.ge80a0c044ae-goog