[PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE

[Marc Zyngier]

CPUs stuck in VHE mode need some additional care if the kernel
is compiled without CONFIG_ARM64_VHE.

Treat this case as another version of a mismatched boot, and
prevent KVM from being initialised. The machine will boot in
some bizarre state, using TPIDR_EL1 instead of TPIDR_EL2, but
otherwise be functional.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/include/asm/virt.h | 18 +++++++++++++-----
 arch/arm64/kvm/va_layout.c    |  9 +++++++++
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 7379f35ae2c6..69bc4e26aa26 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -72,6 +72,11 @@ void __hyp_reset_vectors(void);
 
 DECLARE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
 
+static inline bool is_kernel_in_hyp_mode(void)
+{
+	return read_sysreg(CurrentEL) == CurrentEL_EL2;
+}
+
 /* Reports the availability of HYP mode */
 static inline bool is_hyp_mode_available(void)
 {
@@ -83,6 +88,10 @@ static inline bool is_hyp_mode_available(void)
 	    static_branch_likely(&kvm_protected_mode_initialized))
 		return true;
 
+	/* Catch braindead CPUs */
+	if (!IS_ENABLED(CONFIG_ARM64_VHE) && is_kernel_in_hyp_mode())
+		return false;
+
 	return (__boot_cpu_mode[0] == BOOT_CPU_MODE_EL2 &&
 		__boot_cpu_mode[1] == BOOT_CPU_MODE_EL2);
 }
@@ -98,12 +107,11 @@ static inline bool is_hyp_mode_mismatched(void)
 	    static_branch_likely(&kvm_protected_mode_initialized))
 		return false;
 
-	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
-}
+	/* Catch braindead CPUs */
+	if (!IS_ENABLED(CONFIG_ARM64_VHE) && is_kernel_in_hyp_mode())
+		return true;
 
-static inline bool is_kernel_in_hyp_mode(void)
-{
-	return read_sysreg(CurrentEL) == CurrentEL_EL2;
+	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
 }
 
 static __always_inline bool has_vhe(void)
diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c
index 978301392d67..edb048654e00 100644
--- a/arch/arm64/kvm/va_layout.c
+++ b/arch/arm64/kvm/va_layout.c
@@ -156,6 +156,9 @@ void __init kvm_update_va_mask(struct alt_instr *alt,
 {
 	int i;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 5);
 
 	for (i = 0; i < nr_inst; i++) {
@@ -191,6 +194,9 @@ void kvm_patch_vector_branch(struct alt_instr *alt,
 	u64 addr;
 	u32 insn;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 4);
 
 	if (!cpus_have_const_cap(ARM64_SPECTRE_V3A) || WARN_ON_ONCE(has_vhe()))
@@ -244,6 +250,9 @@ static void generate_mov_q(u64 val, __le32 *origptr, __le32 *updptr, int nr_inst
 {
 	u32 insn, oinsn, rd;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 4);
 
 	/* Compute target register */
-- 
2.29.2