powerpc/64s: early boot machine check handler

Use the early boot interrupt fixup in the machine check handler to allow
the machine check handler to run before interrupt endian is set up.
Branch to an early boot handler that just does a basic crash, which
allows it to run before ppc_md is set up. MSR[ME] is enabled on the boot
CPU earlier, and the machine check stack is temporarily set to the
middle of the init task stack.

This allows machine checks (e.g., due to invalid data access in real
mode) to print something useful earlier in boot (as soon as udbg is set
up, if CONFIG_PPC_EARLY_DEBUG=y).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926055620.2676869-3-npiggin@gmail.com

3 files changed, 33 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index c1ce7deeeb6e..8d658c740db8 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1134,6 +1134,7 @@ INT_DEFINE_BEGIN(machine_check)
 INT_DEFINE_END(machine_check)
 
 EXC_REAL_BEGIN(machine_check, 0x200, 0x100)
+	EARLY_BOOT_FIXUP
 	GEN_INT_ENTRY machine_check_early, virt=0
 EXC_REAL_END(machine_check, 0x200, 0x100)
 EXC_VIRT_NONE(0x4200, 0x100)
@@ -1198,6 +1199,9 @@ BEGIN_FTR_SECTION
 	bl	enable_machine_check
 END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
+BEGIN_FTR_SECTION
+	bl	machine_check_early_boot
+END_FTR_SECTION(0, 1)     // nop out after boot
 	bl	machine_check_early
 	std	r3,RESULT(r1)	/* Save result */
 	ld	r12,_MSR(r1)
@@ -3096,7 +3100,7 @@ CLOSE_FIXED_SECTION(virt_trampolines);
 USE_TEXT_SECTION()
 
 /* MSR[RI] should be clear because this uses SRR[01] */
-enable_machine_check:
+_GLOBAL(enable_machine_check)
 	mflr	r0
 	bcl	20,31,$+4
 0:	mflr	r3
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index e1ac803c9046..f50476da2f2c 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -34,6 +34,7 @@
 #include <linux/of.h>
 #include <linux/of_fdt.h>
 
+#include <asm/asm-prototypes.h>
 #include <asm/kvm_guest.h>
 #include <asm/io.h>
 #include <asm/kdump.h>
@@ -180,6 +181,16 @@ static void __init fixup_boot_paca(void)
 {
 	/* The boot cpu is started */
 	get_paca()->cpu_start = 1;
+#ifdef CONFIG_PPC_BOOK3S_64
+	/*
+	 * Give the early boot machine check stack somewhere to use, use
+	 * half of the init stack. This is a bit hacky but there should not be
+	 * deep stack usage in early init so shouldn't overflow it or overwrite
+	 * things.
+	 */
+	get_paca()->mc_emergency_sp = (void *)&init_thread_union +
+		(THREAD_SIZE/2);
+#endif
 	/* Allow percpu accesses to work until we setup percpu data */
 	get_paca()->data_offset = 0;
 	/* Mark interrupts soft and hard disabled in PACA */
@@ -357,6 +368,9 @@ void __init early_setup(unsigned long dt_ptr)
 
 	/* -------- printk is now safe to use ------- */
 
+	if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && (mfmsr() & MSR_HV))
+		enable_machine_check();
+
 	/* Try new device tree based feature discovery ... */
 	if (!dt_cpu_ftrs_init(__va(dt_ptr)))
 		/* Otherwise use the old style CPU table */
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 62ec50a7a8ef..9bdd79aa51cf 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -68,6 +68,7 @@
 #include <asm/stacktrace.h>
 #include <asm/nmi.h>
 #include <asm/disassemble.h>
+#include <asm/udbg.h>
 
 #if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC_CORE)
 int (*__debugger)(struct pt_regs *regs) __read_mostly;
@@ -850,6 +851,19 @@ bail:
 }
 
 #ifdef CONFIG_PPC_BOOK3S_64
+DEFINE_INTERRUPT_HANDLER_RAW(machine_check_early_boot)
+{
+	udbg_printf("Machine check (early boot)\n");
+	udbg_printf("SRR0=0x%016lx   SRR1=0x%016lx\n", regs->nip, regs->msr);
+	udbg_printf(" DAR=0x%016lx  DSISR=0x%08lx\n", regs->dar, regs->dsisr);
+	udbg_printf("  LR=0x%016lx     R1=0x%08lx\n", regs->link, regs->gpr[1]);
+	udbg_printf("------\n");
+	die("Machine check (early boot)", regs, SIGBUS);
+	for (;;)
+		;
+	return 0;
+}
+
 DEFINE_INTERRUPT_HANDLER_ASYNC(machine_check_exception_async)
 {
 	__machine_check_exception(regs);