On POWER9 and bad paste instruction (targeting the wrong memory
type) or an invalid opcode in an AMO (atomic memory operation)
will result in specific DSISR bits to be set.
We currently don't understand those bits and thus just "hang"
the process taking constant page faults.
Additionally in the case of paste, it appears that we don't
always get a valid DAR value when the error is a wrong memory
type.
So we need to test those errors early in do_page_fault(),
I chose to generate a SIGBUS which is more correct than a SIGSEGV.
Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
---
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 0266c664014a..5dfce2022f74 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -337,6 +337,21 @@ int do_page_fault(struct pt_regs *regs, unsigned long
address,
}
#endif /* CONFIG_PPC_ICSWX */
+#ifdef CONFIG_PPC_STD_MMU_64
+ /*
+ * These faults indicate a copy/paste on an invalid memory type
+ * or an incorrect AMO operation. They have been observed as not
+ * properly updating the DAR, so handle them early
+ */
+ if (error_code & (DSISR_BAD_COPYPASTE | DSISR_BAD_AMO)) {
+ if (user_mode(regs))
+ _exception(SIGBUS, regs, BUS_OBJERR, address);
+ else
+ rc = SIGBUS;
+ goto bail;
+ }
+#endif /* CONFIG_PPC_STD_MMU_64 */
+
if (notify_page_fault(regs))
goto bail;
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 7e50e47375d6..71f524f2b109 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -282,6 +282,8 @@
#define DSISR_UNSUPP_MMU 0x00080000 /* Unsupported MMU config */
#define DSISR_SET_RC 0x00040000 /* Failed setting of R/C bits */
#define DSISR_PGDIRFAULT 0x00020000 /* Fault on page directory */
+#define DSISR_BAD_COPYPASTE 0x00000008 /* Copy/Paste on wrong mem
type */
+#define DSISR_BAD_AMO 0x00000004 /* Incorrect AMO opcode
*/
#define SPRN_TBRL 0x10C /* Time Base Read Lower Register (user, R/O) */
#define SPRN_TBRU 0x10D /* Time Base Read Upper Register (user, R/O) */
#define SPRN_CIR 0x11B /* Chip Information Register (hyper, R/0) */
