Subject: [PATCH v1 24/24] kvm: arm64: Fix EL2 mode availability checks

From: David Brazdil <[email-masked]>
Date: Mon, 9 Nov 2020 11:32:33 +0000

With protected 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 protected 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 <[email-masked]>
---
 arch/arm64/include/asm/virt.h | 17 +++++++++++++++++
 arch/arm64/kvm/arm.c          |  9 ++++++---
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 2c3124512c00..8159d6010f4b 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -66,10 +66,19 @@ void __hyp_set_vectors(phys_addr_t phys_vector_base);
 void __hyp_reset_vectors(void);
 
 DECLARE_STATIC_KEY_FALSE(kvm_protected_mode);
+DECLARE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
 
 /* Reports the availability of HYP mode */
 static inline bool is_hyp_mode_available(void)
 {
+	/*
+	 * If KVM protected mode 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_likely(&kvm_protected_mode_initialized))
+		return true;
+
 	return (__boot_cpu_mode[0] == BOOT_CPU_MODE_EL2 &&
 		__boot_cpu_mode[1] == BOOT_CPU_MODE_EL2);
 }
@@ -77,6 +86,14 @@ 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 protected mode 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_likely(&kvm_protected_mode_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 c09b95cfa00a..9a2329c92a01 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -48,6 +48,7 @@ __asm__(".arch_extension	virt");
 #endif
 
 DEFINE_STATIC_KEY_FALSE(kvm_protected_mode);
+DEFINE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
 
 DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
 
@@ -1838,12 +1839,14 @@ int kvm_arch_init(void *opaque)
 	if (err)
 		goto out_hyp;
 
-	if (is_kvm_protected_mode())
+	if (is_kvm_protected_mode()) {
+		static_branch_enable(&kvm_protected_mode_initialized);
 		kvm_info("Protected nVHE mode initialized successfully\n");
-	else if (in_hyp_mode)
+	} else if (in_hyp_mode) {
 		kvm_info("VHE mode initialized successfully\n");
-	else
+	} else {
 		kvm_info("Hyp mode initialized successfully\n");
+	}
 
 	return 0;
 
-- 
2.29.2.222.g5d2a92d10f8-goog

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