arm64: record boot mode when entering the kernel

To be able to signal the availability of EL2 to other parts of
the kernel, record the boot mode.

Once booted, two predicates indicate if HYP mode is available,
and if not, whether this is due to a boot mode mismatch or not.
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/virt.h

+/*
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Marc Zyngier <marc.zyngier@arm.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __ASM__VIRT_H
+#define __ASM__VIRT_H
+
+#define BOOT_CPU_MODE_EL2	(0x0e12b007)
+
+#ifndef __ASSEMBLY__
+
+/*
+ * __boot_cpu_mode records what mode CPUs were booted in.
+ * A correctly-implemented bootloader must start all CPUs in the same mode:
+ * In this case, both 32bit halves of __boot_cpu_mode will contain the
+ * same value (either 0 if booted in EL1, BOOT_CPU_MODE_EL2 if booted in EL2).
+ *
+ * Should the bootloader fail to do this, the two values will be different.
+ * This allows the kernel to flag an error when the secondaries have come up.
+ */
+extern u32 __boot_cpu_mode[2];
+
+/* Reports the availability of HYP mode */
+static inline bool is_hyp_mode_available(void)
+{
+	return (__boot_cpu_mode[0] == BOOT_CPU_MODE_EL2 &&
+		__boot_cpu_mode[1] == BOOT_CPU_MODE_EL2);
+}
+
+/* Check if the bootloader has booted CPUs in different modes */
+static inline bool is_hyp_mode_mismatched(void)
+{
+	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
+}
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* ! __ASM__VIRT_H */

arch/arm64/kernel/head.S

@@ -31,6 +31,7 @@
 #include <asm/pgtable-hwdef.h>
 #include <asm/pgtable.h>
 #include <asm/page.h>
+#include <asm/virt.h>
 
 /*
  * swapper_pg_dir is the virtual address of the initial page table. We place
@@ -115,13 +116,13 @@
 
 ENTRY(stext)
 	mov	x21, x0				// x21=FDT
+	bl	__calc_phys_offset		// x24=PHYS_OFFSET, x28=PHYS_OFFSET-PAGE_OFFSET
 	bl	el2_setup			// Drop to EL1
 	mrs	x22, midr_el1			// x22=cpuid
 	mov	x0, x22
 	bl	lookup_processor_type
 	mov	x23, x0				// x23=current cpu_table
 	cbz	x23, __error_p			// invalid processor (x23=0)?
-	bl	__calc_phys_offset		// x24=PHYS_OFFSET, x28=PHYS_OFFSET-PAGE_OFFSET
 	bl	__vet_fdt
 	bl	__create_page_tables		// x25=TTBR0, x26=TTBR1
 	/*
@@ -147,11 +148,16 @@ ENTRY(el2_setup)
 	mrs	x0, CurrentEL
 	cmp	x0, #PSR_MODE_EL2t
 	ccmp	x0, #PSR_MODE_EL2h, #0x4, ne
+	ldr	x0, =__boot_cpu_mode		// Compute __boot_cpu_mode
+	add	x0, x0, x28
 	b.eq	1f
+	str	wzr, [x0]			// Remember we don't have EL2...
 	ret
 
 	/* Hyp configuration. */
-1:	mov	x0, #(1 << 31)			// 64-bit EL1
+1:	ldr	w1, =BOOT_CPU_MODE_EL2
+	str	w1, [x0, #4]			// This CPU has EL2
+	mov	x0, #(1 << 31)			// 64-bit EL1
 	msr	hcr_el2, x0
 
 	/* Generic timers. */
@@ -187,6 +193,19 @@ ENTRY(el2_setup)
 	eret
 ENDPROC(el2_setup)
 
+/*
+ * We need to find out the CPU boot mode long after boot, so we need to
+ * store it in a writable variable.
+ *
+ * This is not in .bss, because we set it sufficiently early that the boot-time
+ * zeroing of .bss would clobber it.
+ */
+	.pushsection	.data
+ENTRY(__boot_cpu_mode)
+	.long	BOOT_CPU_MODE_EL2
+	.long	0
+	.popsection
+
 	.align	3
 2:	.quad	.
 	.quad	PAGE_OFFSET
@@ -202,6 +221,7 @@ ENDPROC(el2_setup)
 	 * cores are held until we're ready for them to initialise.
 	 */
 ENTRY(secondary_holding_pen)
+	bl	__calc_phys_offset		// x24=phys offset
 	bl	el2_setup			// Drop to EL1
 	mrs	x0, mpidr_el1
 	and	x0, x0, #15			// CPU number
@@ -227,7 +247,6 @@ ENTRY(secondary_startup)
 	mov	x23, x0				// x23=current cpu_table
 	cbz	x23, __error_p			// invalid processor (x23=0)?
 
-	bl	__calc_phys_offset		// x24=phys offset
 	pgtbl	x25, x26, x24			// x25=TTBR0, x26=TTBR1
 	ldr	x12, [x23, #CPU_INFO_SETUP]
 	add	x12, x12, x28			// __virt_to_phys