powerpc/64s: add a table of implicit soft-masked addresses

Commit 9d1988ca87dd ("powerpc/64: treat low kernel text as irqs
soft-masked") ends up catching too much code, including ret_from_fork,
and parts of interrupt and syscall return that do not expect to be
interrupts to be soft-masked. If an interrupt gets marked pending,
and then the code proceeds out of the implicit soft-masked region it
will fail to deal with the pending interrupt.

Fix this by adding a new table of addresses which explicitly marks
the regions of code that are soft masked. This table is only checked
for interrupts that below __end_soft_masked, so most kernel interrupts
will not have the overhead of the table search.

Fixes: 9d1988ca87dd ("powerpc/64: treat low kernel text as irqs soft-masked")
Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210630074621.2109197-5-npiggin@gmail.com

1 files changed, 26 insertions, 0 deletions

diff --git a/arch/powerpc/lib/restart_table.c b/arch/powerpc/lib/restart_table.c
index 7cd20757cc33..bccb662c1b7b 100644
--- a/arch/powerpc/lib/restart_table.c
+++ b/arch/powerpc/lib/restart_table.c
@@ -1,15 +1,41 @@
 #include <asm/interrupt.h>
 #include <asm/kprobes.h>
 
+struct soft_mask_table_entry {
+	unsigned long start;
+	unsigned long end;
+};
+
 struct restart_table_entry {
 	unsigned long start;
 	unsigned long end;
 	unsigned long fixup;
 };
 
+extern struct soft_mask_table_entry __start___soft_mask_table[];
+extern struct soft_mask_table_entry __stop___soft_mask_table[];
+
 extern struct restart_table_entry __start___restart_table[];
 extern struct restart_table_entry __stop___restart_table[];
 
+/* Given an address, look for it in the soft mask table */
+bool search_kernel_soft_mask_table(unsigned long addr)
+{
+	struct soft_mask_table_entry *smte = __start___soft_mask_table;
+
+	while (smte < __stop___soft_mask_table) {
+		unsigned long start = smte->start;
+		unsigned long end = smte->end;
+
+		if (addr >= start && addr < end)
+			return true;
+
+		smte++;
+	}
+	return false;
+}
+NOKPROBE_SYMBOL(search_kernel_soft_mask_table);
+
 /* Given an address, look for it in the kernel exception table */
 unsigned long search_kernel_restart_table(unsigned long addr)
 {