[IA64] MCA recovery: kernel context recovery table

Memory errors encountered by user applications may surface
when the CPU is running in kernel context.  The current code
will not attempt recovery if the MCA surfaces in kernel
context (privilage mode 0).  This patch adds a check for cases
where the user initiated the load that surfaces in kernel
interrupt code.

An example is a user process lauching a load from memory
and the data in memory had bad ECC.  Before the bad data
gets to the CPU register, and interrupt comes in.  The
code jumps to the IVT interrupt entry point and begins
execution in kernel context.  The process of saving the
user registers (SAVE_REST) causes the bad data to be loaded
into a CPU register, triggering the MCA.  The MCA surfaces in
kernel context, even though the load was initiated from
user context.

As suggested by David and Tony, this patch uses an exception
table like approach, puting the tagged recovery addresses in
a searchable table.  One difference from the exception table
is that MCAs do not surface in precise places (such as with
a TLB miss), so instead of tagging specific instructions,
address ranges are registers.  A single macro is used to do
the tagging, with the input parameter being the label
of the starting address and the macro being the ending
address.  This limits clutter in the code.

This patch only tags one spot, the interrupt ivt entry.
Testing showed that spot to be a "heavy hitter" with
MCAs surfacing while saving user registers.  Other spots
can be added as needed by adding a single macro.

Signed-off-by: Russ Anderson (rja@sgi.com)
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 73 insertions, 25 deletions

diff --git a/arch/ia64/kernel/mca.c b/arch/ia64/kernel/mca.c
index cedcae713e9f..87ff7fe33cfb 100644
--- a/arch/ia64/kernel/mca.c
+++ b/arch/ia64/kernel/mca.c
@@ -83,6 +83,7 @@
 #include <asm/irq.h>
 #include <asm/hw_irq.h>
 
+#include "mca_drv.h"
 #include "entry.h"
 
 #if defined(IA64_MCA_DEBUG_INFO)
@@ -281,6 +282,50 @@ ia64_mca_log_sal_error_record(int sal_info_type)
 		ia64_sal_clear_state_info(sal_info_type);
 }
 
+/*
+ * search_mca_table
+ *  See if the MCA surfaced in an instruction range
+ *  that has been tagged as recoverable.
+ *
+ *  Inputs
+ *	first	First address range to check
+ *	last	Last address range to check
+ *	ip	Instruction pointer, address we are looking for
+ *
+ * Return value:
+ *      1 on Success (in the table)/ 0 on Failure (not in the  table)
+ */
+int
+search_mca_table (const struct mca_table_entry *first,
+                const struct mca_table_entry *last,
+                unsigned long ip)
+{
+        const struct mca_table_entry *curr;
+        u64 curr_start, curr_end;
+
+        curr = first;
+        while (curr <= last) {
+                curr_start = (u64) &curr->start_addr + curr->start_addr;
+                curr_end = (u64) &curr->end_addr + curr->end_addr;
+
+                if ((ip >= curr_start) && (ip <= curr_end)) {
+                        return 1;
+                }
+                curr++;
+        }
+        return 0;
+}
+
+/* Given an address, look for it in the mca tables. */
+int mca_recover_range(unsigned long addr)
+{
+	extern struct mca_table_entry __start___mca_table[];
+	extern struct mca_table_entry __stop___mca_table[];
+
+	return search_mca_table(__start___mca_table, __stop___mca_table-1, addr);
+}
+EXPORT_SYMBOL_GPL(mca_recover_range);
+
 #ifdef CONFIG_ACPI
 
 int cpe_vector = -1;
@@ -747,31 +792,34 @@ ia64_mca_modify_original_stack(struct pt_regs *regs,
 		ia64_mca_modify_comm(previous_current);
 		goto no_mod;
 	}
-	if (r13 != sos->prev_IA64_KR_CURRENT) {
-		msg = "inconsistent previous current and r13";
-		goto no_mod;
-	}
-	if ((r12 - r13) >= KERNEL_STACK_SIZE) {
-		msg = "inconsistent r12 and r13";
-		goto no_mod;
-	}
-	if ((ar_bspstore - r13) >= KERNEL_STACK_SIZE) {
-		msg = "inconsistent ar.bspstore and r13";
-		goto no_mod;
-	}
-	va.p = old_bspstore;
-	if (va.f.reg < 5) {
-		msg = "old_bspstore is in the wrong region";
-		goto no_mod;
-	}
-	if ((ar_bsp - r13) >= KERNEL_STACK_SIZE) {
-		msg = "inconsistent ar.bsp and r13";
-		goto no_mod;
-	}
-	size += (ia64_rse_skip_regs(old_bspstore, slots) - old_bspstore) * 8;
-	if (ar_bspstore + size > r12) {
-		msg = "no room for blocked state";
-		goto no_mod;
+
+	if (!mca_recover_range(ms->pmsa_iip)) {
+		if (r13 != sos->prev_IA64_KR_CURRENT) {
+			msg = "inconsistent previous current and r13";
+			goto no_mod;
+		}
+		if ((r12 - r13) >= KERNEL_STACK_SIZE) {
+			msg = "inconsistent r12 and r13";
+			goto no_mod;
+		}
+		if ((ar_bspstore - r13) >= KERNEL_STACK_SIZE) {
+			msg = "inconsistent ar.bspstore and r13";
+			goto no_mod;
+		}
+		va.p = old_bspstore;
+		if (va.f.reg < 5) {
+			msg = "old_bspstore is in the wrong region";
+			goto no_mod;
+		}
+		if ((ar_bsp - r13) >= KERNEL_STACK_SIZE) {
+			msg = "inconsistent ar.bsp and r13";
+			goto no_mod;
+		}
+		size += (ia64_rse_skip_regs(old_bspstore, slots) - old_bspstore) * 8;
+		if (ar_bspstore + size > r12) {
+			msg = "no room for blocked state";
+			goto no_mod;
+		}
 	}
 
 	ia64_mca_modify_comm(previous_current);