arm64: Save state of HCR_EL2.E2H before switch to EL1

As we're about to switch the way E2H-stuck CPUs boot, save
the boot CPU E2H state as a flag tied to the boot mode
that can then be checked by the idreg override code.

This allows us to replace the is_kernel_in_hyp_mode() check
with a simple comparison with this state, even when running
at EL1. Note that this flag isn't saved in __boot_cpu_mode,
and is only kept in a register in the assembly code.

Use with caution.
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220630160500.1536744-3-maz@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/virt.h

@@ -49,6 +49,13 @@
 #define BOOT_CPU_MODE_EL1	(0xe11)
 #define BOOT_CPU_MODE_EL2	(0xe12)
 
+/*
+ * Flags returned together with the boot mode, but not preserved in
+ * __boot_cpu_mode. Used by the idreg override code to work out the
+ * boot state.
+ */
+#define BOOT_CPU_FLAG_E2H	BIT_ULL(32)
+
 #ifndef __ASSEMBLY__
 
 #include <asm/ptrace.h>

arch/arm64/kernel/head.S

@@ -457,6 +457,7 @@ SYM_FUNC_START_LOCAL(__primary_switched)
 	bl	kasan_early_init
 #endif
 	mov	x0, x22				// pass FDT address in x0
+	mov	x1, x20				// pass the full boot status
 	bl	init_feature_override		// Parse cpu feature overrides
 	mov	x0, x20
 	bl	finalise_el2			// Prefer VHE if possible
@@ -479,8 +480,9 @@ SYM_FUNC_END(__primary_switched)
  * Since we cannot always rely on ERET synchronizing writes to sysregs (e.g. if
  * SCTLR_ELx.EOS is clear), we place an ISB prior to ERET.
  *
- * Returns either BOOT_CPU_MODE_EL1 or BOOT_CPU_MODE_EL2 in w0 if
- * booted in EL1 or EL2 respectively.
+ * Returns either BOOT_CPU_MODE_EL1 or BOOT_CPU_MODE_EL2 in x0 if
+ * booted in EL1 or EL2 respectively, with the top 32 bits containing
+ * potential context flags. These flags are *not* stored in __boot_cpu_mode.
  */
 SYM_FUNC_START(init_kernel_el)
 	mrs	x0, CurrentEL
@@ -545,6 +547,7 @@ __cpu_stick_to_vhe:
 	mov	x0, #HVC_FINALISE_EL2
 	hvc	#0
 	mov	x0, #BOOT_CPU_MODE_EL2
+	orr	x0, x0, #BOOT_CPU_FLAG_E2H
 	ret
 SYM_FUNC_END(init_kernel_el)
 

arch/arm64/kernel/idreg-override.c

@@ -19,6 +19,8 @@
 #define FTR_ALIAS_NAME_LEN	30
 #define FTR_ALIAS_OPTION_LEN	116
 
+static u64 __boot_status __initdata;
+
 struct ftr_set_desc {
 	char 				name[FTR_DESC_NAME_LEN];
 	struct arm64_ftr_override	*override;
@@ -37,7 +39,8 @@ static bool __init mmfr1_vh_filter(u64 val)
 	 * the user was trying to force nVHE on us, proceed with
 	 * attitude adjustment.
 	 */
-	return !(is_kernel_in_hyp_mode() && val == 0);
+	return !(__boot_status == (BOOT_CPU_FLAG_E2H | BOOT_CPU_MODE_EL2) &&
+		 val == 0);
 }
 
 static const struct ftr_set_desc mmfr1 __initconst = {
@@ -229,9 +232,9 @@ static __init void parse_cmdline(const void *fdt)
 }
 
 /* Keep checkers quiet */
-void init_feature_override(const void *fdt);
+void init_feature_override(const void *fdt, u64 boot_status);
 
-asmlinkage void __init init_feature_override(const void *fdt)
+asmlinkage void __init init_feature_override(const void *fdt, u64 boot_status)
 {
 	int i;
 
@@ -242,6 +245,8 @@ asmlinkage void __init init_feature_override(const void *fdt)
 		}
 	}
 
+	__boot_status = boot_status;
+
 	parse_cmdline(fdt);
 
 	for (i = 0; i < ARRAY_SIZE(regs); i++) {