[PATCH v2 04/11] powerpc: Mark [h]ssr_valid accesses in check_return_regs_valid

[Rohan McLure]

Checks to see if the [H]SRR registers have been clobbered by (soft)
NMI interrupts imply the possibility for a data race on the
[h]srr_valid entries in the PACA. Annotate accesses to these fields with
READ_ONCE, removing the need for the barrier.

The diagnostic can use plain-access reads and writes, but annotate with
data_race.

Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com>
Reported-by: Michael Ellerman <m...@ellerman.id.au>
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/include/asm/ptrace.h |  4 ++--
 arch/powerpc/kernel/interrupt.c   | 14 ++++++--------
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/include/asm/ptrace.h 
b/arch/powerpc/include/asm/ptrace.h
index 0eb90a013346..9db8b16567e2 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -180,8 +180,8 @@ void do_syscall_trace_leave(struct pt_regs *regs);
 static inline void set_return_regs_changed(void)
 {
 #ifdef CONFIG_PPC_BOOK3S_64
-       local_paca->hsrr_valid = 0;
-       local_paca->srr_valid = 0;
+       WRITE_ONCE(local_paca->hsrr_valid, 0);
+       WRITE_ONCE(local_paca->srr_valid, 0);
 #endif
 }
 
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index e34c72285b4e..1f033f11b871 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -125,7 +125,7 @@ static notrace void check_return_regs_valid(struct pt_regs 
*regs)
        case 0x1600:
        case 0x1800:
                validp = &local_paca->hsrr_valid;
-               if (!*validp)
+               if (!READ_ONCE(*validp))
                        return;
 
                srr0 = mfspr(SPRN_HSRR0);
@@ -135,7 +135,7 @@ static notrace void check_return_regs_valid(struct pt_regs 
*regs)
                break;
        default:
                validp = &local_paca->srr_valid;
-               if (!*validp)
+               if (!READ_ONCE(*validp))
                        return;
 
                srr0 = mfspr(SPRN_SRR0);
@@ -161,19 +161,17 @@ static notrace void check_return_regs_valid(struct 
pt_regs *regs)
         * such things will get caught most of the time, statistically
         * enough to be able to get a warning out.
         */
-       barrier();
-
-       if (!*validp)
+       if (!READ_ONCE(*validp))
                return;
 
-       if (!warned) {
-               warned = true;
+       if (!data_race(warned)) {
+               data_race(warned = true);
                printk("%sSRR0 was: %lx should be: %lx\n", h, srr0, regs->nip);
                printk("%sSRR1 was: %lx should be: %lx\n", h, srr1, regs->msr);
                show_regs(regs);
        }
 
-       *validp = 0; /* fixup */
+       WRITE_ONCE(*validp, 0); /* fixup */
 #endif
 }
 
-- 
2.37.2