powerpc/64: allow alternate return locations for soft-masked interrupts

The exception table fixup adjusts a failed page fault's interrupt return
location if it was taken at an address specified in the exception table,
to a corresponding fixup handler address.

Introduce a variation of that idea which adds a fixup table for NMIs and
soft-masked asynchronous interrupts. This will be used to protect
certain critical sections that are sensitive to being clobbered by
interrupts coming in (due to using the same SPRs and/or irq soft-mask
state).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-10-npiggin@gmail.com

2 files changed, 31 insertions, 1 deletions

diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index cc1a8a0f311e..4c92c80454f3 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -42,7 +42,7 @@ obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o copypage_power7.o \
 			       memcpy_power7.o
 
 obj64-y	+= copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
-	   memcpy_64.o copy_mc_64.o
+	   memcpy_64.o copy_mc_64.o restart_table.o
 
 ifndef CONFIG_PPC_QUEUED_SPINLOCKS
 obj64-$(CONFIG_SMP)	+= locks.o
diff --git a/arch/powerpc/lib/restart_table.c b/arch/powerpc/lib/restart_table.c
new file mode 100644
index 000000000000..7cd20757cc33
--- /dev/null
+++ b/arch/powerpc/lib/restart_table.c
@@ -0,0 +1,30 @@
+#include <asm/interrupt.h>
+#include <asm/kprobes.h>
+
+struct restart_table_entry {
+	unsigned long start;
+	unsigned long end;
+	unsigned long fixup;
+};
+
+extern struct restart_table_entry __start___restart_table[];
+extern struct restart_table_entry __stop___restart_table[];
+
+/* Given an address, look for it in the kernel exception table */
+unsigned long search_kernel_restart_table(unsigned long addr)
+{
+	struct restart_table_entry *rte = __start___restart_table;
+
+	while (rte < __stop___restart_table) {
+		unsigned long start = rte->start;
+		unsigned long end = rte->end;
+		unsigned long fixup = rte->fixup;
+
+		if (addr >= start && addr < end)
+			return fixup;
+
+		rte++;
+	}
+	return 0;
+}
+NOKPROBE_SYMBOL(search_kernel_restart_table);