Subject: [kvm-unit-tests PATCH 08/32] powerpc/sprs: Avoid taking PMU interrupts caused by register fuzzing

From: Nicholas Piggin <[email-masked]>
Date: Mon, 26 Feb 2024 20:11:54 +1000

Storing certain values in MMCR0 can cause PMU interrupts when msleep
enables MSR[EE], and this crashes the test. Freeze the PMU counters
and clear any PMU exception before calling msleep.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 lib/powerpc/asm/reg.h |  4 ++++
 powerpc/sprs.c        | 17 +++++++++++------
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/lib/powerpc/asm/reg.h b/lib/powerpc/asm/reg.h
index 1f991288e..c80b32059 100644
--- a/lib/powerpc/asm/reg.h
+++ b/lib/powerpc/asm/reg.h
@@ -24,6 +24,10 @@
 #define   PVR_VER_POWER10	UL(0x00800000)
 #define SPR_HSRR0	0x13a
 #define SPR_HSRR1	0x13b
+#define SPR_MMCR0	0x31b
+#define   MMCR0_FC		UL(0x80000000)
+#define   MMCR0_PMAE		UL(0x04000000)
+#define   MMCR0_PMAO		UL(0x00000080)
 
 /* Machine State Register definitions: */
 #define MSR_EE_BIT	15			/* External Interrupts Enable */
diff --git a/powerpc/sprs.c b/powerpc/sprs.c
index 44edd0d7b..cb1d6c980 100644
--- a/powerpc/sprs.c
+++ b/powerpc/sprs.c
@@ -476,12 +476,7 @@ static void set_sprs(uint64_t val)
 			continue;
 		if (sprs[i].type & SPR_HARNESS)
 			continue;
-		if (!strcmp(sprs[i].name, "MMCR0")) {
-			/* XXX: could use a comment or better abstraction! */
-			__mtspr(i, (val & 0xfffffffffbab3fffULL) | 0xfa0b2070);
-		} else {
-			__mtspr(i, val);
-		}
+		__mtspr(i, val);
 	}
 }
 
@@ -538,6 +533,16 @@ int main(int argc, char **argv)
 		if (sprs[895].name)
 			before[895] = mfspr(895);
 	} else {
+		/*
+		 * msleep will enable MSR[EE] and take a decrementer
+		 * interrupt. Must account for changed registers and
+		 * prevent taking unhandled interrupts.
+		 */
+		/* Prevent PMU interrupt */
+		mtspr(SPR_MMCR0, (mfspr(SPR_MMCR0) | MMCR0_FC) &
+					~(MMCR0_PMAO | MMCR0_PMAE));
+		before[SPR_MMCR0] = mfspr(SPR_MMCR0);
+		before[779] = mfspr(SPR_MMCR0);
 		msleep(2000);
 
 		/* Reload regs changed by dec interrupt */
-- 
2.42.0