powerpc/book3s: Recover from MC in sapphire on SCOM read via MMIO.

Detect and recover from machine check when inside opal on a special
scom load instructions. On specific SCOM read via MMIO we may get a machine
check exception with SRR0 pointing inside opal. To recover from MC
in this scenario, get a recovery instruction address and return to it from
MC.

OPAL will export the machine check recoverable ranges through
device tree node mcheck-recoverable-ranges under ibm,opal:

# hexdump /proc/device-tree/ibm,opal/mcheck-recoverable-ranges
0000000 0000 0000 3000 2804 0000 000c 0000 0000
0000010 3000 2814 0000 0000 3000 27f0 0000 000c
0000020 0000 0000 3000 2814 xxxx xxxx xxxx xxxx
0000030 llll llll yyyy yyyy yyyy yyyy
...
...
#

where:
xxxx xxxx xxxx xxxx = Starting instruction address
llll llll = Length of the address range.
yyyy yyyy yyyy yyyy = recovery address

Each recoverable address range entry is (start address, len,
recovery address), 2 cells each for start and recovery address, 1 cell for
len, totalling 5 cells per entry. During kernel boot time, build up the
recovery table with the list of recovery ranges from device-tree node which
will be used during machine check exception to recover from MMIO SCOM UE.

Signed-off-by: Mahesh Salgaonkar <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/include/asm/machdep.h

···
 	int		(*system_reset_exception)(struct pt_regs *regs);
 	int 		(*machine_check_exception)(struct pt_regs *regs);
 
+	/* Called during machine check exception to retrive fixup address. */
+	bool		(*mce_check_early_recovery)(struct pt_regs *regs);
+
 	/* Motherboard/chipset features. This is a kind of general purpose
 	 * hook used to control some machine specific features (like reset
 	 * lines, chip power control, etc...).

arch/powerpc/include/asm/mce.h

···
 #define MCE_EVENT_DONTRELEASE	false
 
 extern void save_mce_event(struct pt_regs *regs, long handled,
-			   struct mce_error_info *mce_err, uint64_t addr);
+			   struct mce_error_info *mce_err, uint64_t nip,
+			   uint64_t addr);
 extern int get_mce_event(struct machine_check_event *mce, bool release);
 extern void release_mce_event(void);
 extern void machine_check_queue_event(void);

arch/powerpc/include/asm/opal.h

···
 
 /* Internal functions */
 extern int early_init_dt_scan_opal(unsigned long node, const char *uname, int depth, void *data);
+extern int early_init_dt_scan_recoverable_ranges(unsigned long node,
+				 const char *uname, int depth, void *data);
 
 extern int opal_get_chars(uint32_t vtermno, char *buf, int count);
 extern int opal_put_chars(uint32_t vtermno, const char *buf, int total_len);
···
 extern void opal_flash_init(void);
 
 extern int opal_machine_check(struct pt_regs *regs);
+extern bool opal_mce_check_early_recovery(struct pt_regs *regs);
 
 extern void opal_shutdown(void);
 

arch/powerpc/kernel/mce.c

···
  */
 void save_mce_event(struct pt_regs *regs, long handled,
 		    struct mce_error_info *mce_err,
-		    uint64_t addr)
+		    uint64_t nip, uint64_t addr)
 {
 	uint64_t srr1;
 	int index = __get_cpu_var(mce_nest_count)++;
···
 
 	/* Populate generic machine check info */
 	mce->version = MCE_V1;
-	mce->srr0 = regs->nip;
+	mce->srr0 = nip;
 	mce->srr1 = regs->msr;
 	mce->gpr3 = regs->gpr[3];
 	mce->in_use = 1;

arch/powerpc/kernel/mce_power.c

···
 #include <linux/ptrace.h>
 #include <asm/mmu.h>
 #include <asm/mce.h>
+#include <asm/machdep.h>
 
 /* flush SLBs and reload */
 static void flush_and_reload_slb(void)
···
 	}
 }
 
+static long mce_handle_ue_error(struct pt_regs *regs)
+{
+	long handled = 0;
+
+	/*
+	 * On specific SCOM read via MMIO we may get a machine check
+	 * exception with SRR0 pointing inside opal. If that is the
+	 * case OPAL may have recovery address to re-read SCOM data in
+	 * different way and hence we can recover from this MC.
+	 */
+
+	if (ppc_md.mce_check_early_recovery) {
+		if (ppc_md.mce_check_early_recovery(regs))
+			handled = 1;
+	}
+	return handled;
+}
+
 long __machine_check_early_realmode_p7(struct pt_regs *regs)
 {
-	uint64_t srr1, addr;
+	uint64_t srr1, nip, addr;
 	long handled = 1;
 	struct mce_error_info mce_error_info = { 0 };
 
 	srr1 = regs->msr;
+	nip = regs->nip;
 
 	/*
 	 * Handle memory errors depending whether this was a load/store or
···
 		addr = regs->nip;
 	}
 
-	save_mce_event(regs, handled, &mce_error_info, addr);
+	/* Handle UE error. */
+	if (mce_error_info.error_type == MCE_ERROR_TYPE_UE)
+		handled = mce_handle_ue_error(regs);
+
+	save_mce_event(regs, handled, &mce_error_info, nip, addr);
 	return handled;
 }
 
···
 
 long __machine_check_early_realmode_p8(struct pt_regs *regs)
 {
-	uint64_t srr1, addr;
+	uint64_t srr1, nip, addr;
 	long handled = 1;
 	struct mce_error_info mce_error_info = { 0 };
 
 	srr1 = regs->msr;
+	nip = regs->nip;
 
 	if (P7_SRR1_MC_LOADSTORE(srr1)) {
 		handled = mce_handle_derror_p8(regs->dsisr);
···
 		addr = regs->nip;
 	}
 
-	save_mce_event(regs, handled, &mce_error_info, addr);
+	/* Handle UE error. */
+	if (mce_error_info.error_type == MCE_ERROR_TYPE_UE)
+		handled = mce_handle_ue_error(regs);
+
+	save_mce_event(regs, handled, &mce_error_info, nip, addr);
 	return handled;
 }

arch/powerpc/kernel/prom.c

···
 	spinning_secondaries = boot_cpu_count - 1;
 #endif
 
+#ifdef CONFIG_PPC_POWERNV
+	/* Scan and build the list of machine check recoverable ranges */
+	of_scan_flat_dt(early_init_dt_scan_recoverable_ranges, NULL);
+#endif
+
 	DBG(" <- early_init_devtree()\n");
 }
 

arch/powerpc/platforms/powernv/opal.c

···
 #include <linux/sched.h>
 #include <linux/kobject.h>
 #include <linux/delay.h>
+#include <linux/memblock.h>
 #include <asm/opal.h>
 #include <asm/firmware.h>
 #include <asm/mce.h>
···
 struct opal {
 	u64 base;
 	u64 entry;
+	u64 size;
 } opal;
+
+struct mcheck_recoverable_range {
+	u64 start_addr;
+	u64 end_addr;
+	u64 recover_addr;
+};
+
+static struct mcheck_recoverable_range *mc_recoverable_range;
+static int mc_recoverable_range_len;
 
 static struct device_node *opal_node;
 static DEFINE_SPINLOCK(opal_write_lock);
···
 int __init early_init_dt_scan_opal(unsigned long node,
 				   const char *uname, int depth, void *data)
 {
-	const void *basep, *entryp;
-	unsigned long basesz, entrysz;
+	const void *basep, *entryp, *sizep;
+	unsigned long basesz, entrysz, runtimesz;
 
 	if (depth != 1 || strcmp(uname, "ibm,opal") != 0)
 		return 0;
 
 	basep  = of_get_flat_dt_prop(node, "opal-base-address", &basesz);
 	entryp = of_get_flat_dt_prop(node, "opal-entry-address", &entrysz);
+	sizep = of_get_flat_dt_prop(node, "opal-runtime-size", &runtimesz);
 
-	if (!basep || !entryp)
+	if (!basep || !entryp || !sizep)
 		return 1;
 
 	opal.base = of_read_number(basep, basesz/4);
 	opal.entry = of_read_number(entryp, entrysz/4);
+	opal.size = of_read_number(sizep, runtimesz/4);
 
 	pr_debug("OPAL Base  = 0x%llx (basep=%p basesz=%ld)\n",
 		 opal.base, basep, basesz);
 	pr_debug("OPAL Entry = 0x%llx (entryp=%p basesz=%ld)\n",
 		 opal.entry, entryp, entrysz);
+	pr_debug("OPAL Entry = 0x%llx (sizep=%p runtimesz=%ld)\n",
+		 opal.size, sizep, runtimesz);
 
 	powerpc_firmware_features |= FW_FEATURE_OPAL;
 	if (of_flat_dt_is_compatible(node, "ibm,opal-v3")) {
···
 		printk("OPAL V1 detected !\n");
 	}
 
+	return 1;
+}
+
+int __init early_init_dt_scan_recoverable_ranges(unsigned long node,
+				   const char *uname, int depth, void *data)
+{
+	unsigned long i, size;
+	const __be32 *prop;
+
+	if (depth != 1 || strcmp(uname, "ibm,opal") != 0)
+		return 0;
+
+	prop = of_get_flat_dt_prop(node, "mcheck-recoverable-ranges", &size);
+
+	if (!prop)
+		return 1;
+
+	pr_debug("Found machine check recoverable ranges.\n");
+
+	/*
+	 * Allocate a buffer to hold the MC recoverable ranges. We would be
+	 * accessing them in real mode, hence it needs to be within
+	 * RMO region.
+	 */
+	mc_recoverable_range =__va(memblock_alloc_base(size, __alignof__(u64),
+							ppc64_rma_size));
+	memset(mc_recoverable_range, 0, size);
+
+	/*
+	 * Each recoverable address entry is an (start address,len,
+	 * recover address) pair, * 2 cells each, totalling 4 cells per entry.
+	 */
+	for (i = 0; i < size / (sizeof(*prop) * 5); i++) {
+		mc_recoverable_range[i].start_addr =
+					of_read_number(prop + (i * 5) + 0, 2);
+		mc_recoverable_range[i].end_addr =
+					mc_recoverable_range[i].start_addr +
+					of_read_number(prop + (i * 5) + 2, 1);
+		mc_recoverable_range[i].recover_addr =
+					of_read_number(prop + (i * 5) + 3, 2);
+
+		pr_debug("Machine check recoverable range: %llx..%llx: %llx\n",
+				mc_recoverable_range[i].start_addr,
+				mc_recoverable_range[i].end_addr,
+				mc_recoverable_range[i].recover_addr);
+	}
+	mc_recoverable_range_len = i;
 	return 1;
 }
 
···
 	if (opal_recover_mce(regs, &evt))
 		return 1;
 	return 0;
+}
+
+static uint64_t find_recovery_address(uint64_t nip)
+{
+	int i;
+
+	for (i = 0; i < mc_recoverable_range_len; i++)
+		if ((nip >= mc_recoverable_range[i].start_addr) &&
+		    (nip < mc_recoverable_range[i].end_addr))
+		    return mc_recoverable_range[i].recover_addr;
+	return 0;
+}
+
+bool opal_mce_check_early_recovery(struct pt_regs *regs)
+{
+	uint64_t recover_addr = 0;
+
+	if (!opal.base || !opal.size)
+		goto out;
+
+	if ((regs->nip >= opal.base) &&
+			(regs->nip <= (opal.base + opal.size)))
+		recover_addr = find_recovery_address(regs->nip);
+
+	/*
+	 * Setup regs->nip to rfi into fixup address.
+	 */
+	if (recover_addr)
+		regs->nip = recover_addr;
+
+out:
+	return !!recover_addr;
 }
 
 static irqreturn_t opal_interrupt(int irq, void *data)

arch/powerpc/platforms/powernv/setup.c

···
 	ppc_md.power_off = pnv_power_off;
 	ppc_md.halt = pnv_halt;
 	ppc_md.machine_check_exception = opal_machine_check;
+	ppc_md.mce_check_early_recovery = opal_mce_check_early_recovery;
 }
 
 #ifdef CONFIG_PPC_POWERNV_RTAS