[PATCH 2/6] arm64: Save state of HCR_EL2.E2H before switch to EL1

[Marc Zyngier]

As we're about to switch the way E2H-stuck CPUs boot, save
the boot CPU E2H state into a global variable that can then be
checked by the iderg override code.

This allows us to replace the is_kernel_in_hyp_mode() check
with a simple comparison with this variable, even when running
at EL1.  Note that the variable's validity is pretty short
(it cannot be trusted once a secondary has booted).

Use with caution.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kernel/head.S           | 11 +++++++++++
 arch/arm64/kernel/idreg-override.c | 10 +++++-----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index f8550a939a6e..d35287c22d30 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -527,6 +527,8 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)
 	 */
 	mrs	x0, hcr_el2
 	and	x0, x0, #HCR_E2H
+	adr_l	x1, __e2h_state
+	str	x0, [x1]
 	cbz	x0, 1f
 
 	/* Switching to VHE requires a sane SCTLR_EL1 as a start */
@@ -599,6 +601,15 @@ SYM_DATA_END(__boot_cpu_mode)
 SYM_DATA_START(__early_cpu_boot_status)
 	.quad 	0
 SYM_DATA_END(__early_cpu_boot_status)
+/*
+ * The value of the boot CPU's HCR_EL2.E2H state before dropping to
+ * EL1, so that the idreg override code can work out whether it can
+ * run in nVHE mode. Note that this is meaningless once a secondary
+ * CPU has booted, as it will have been overwritten.
+ */
+SYM_DATA_START(__e2h_state)
+	.quad 	0
+SYM_DATA_END(__e2h_state)
 
 	.popsection
 
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index 8a2ceb591686..6abff337b23b 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -31,13 +31,13 @@ struct ftr_set_desc {
 
 static bool __init mmfr1_vh_filter(u64 val)
 {
+	extern u64 __e2h_state;
 	/*
-	 * If we ever reach this point while running VHE, we're
-	 * guaranteed to be on one of these funky, VHE-stuck CPUs. If
-	 * the user was trying to force nVHE on us, proceed with
-	 * attitude adjustment.
+	 * If the boot CPU has HCR_EL2.E2H set, we're guaranteed to be
+	 * on one of these funky, VHE-stuck CPUs. If the user was
+	 * trying to force nVHE on us, proceed with attitude adjustment.
 	 */
-	return !(is_kernel_in_hyp_mode() && val == 0);
+	return !(__e2h_state != 0 && val == 0);
 }
 
 static const struct ftr_set_desc mmfr1 __initconst = {
-- 
2.34.1