KVM: PPC: Book3S HV: Work around POWER8 performance monitor bugs

This adds workarounds for two hardware bugs in the POWER8 performance
monitor unit (PMU), both related to interrupt generation.  The effect
of these bugs is that PMU interrupts can get lost, leading to tools
such as perf reporting fewer counts and samples than they should.

The first bug relates to the PMAO (perf. mon. alert occurred) bit in
MMCR0; setting it should cause an interrupt, but doesn't.  The other
bug relates to the PMAE (perf. mon. alert enable) bit in MMCR0.
Setting PMAE when a counter is negative and counter negative
conditions are enabled to cause alerts should cause an alert, but
doesn't.

The workaround for the first bug is to create conditions where a
counter will overflow, whenever we are about to restore a MMCR0
value that has PMAO set (and PMAO_SYNC clear).  The workaround for
the second bug is to freeze all counters using MMCR2 before reading
MMCR0.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 57 insertions, 2 deletions

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index ffbb871c2bd8..60fe8ba318cf 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -86,6 +86,12 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
 	lbz	r4, LPPACA_PMCINUSE(r3)
 	cmpwi	r4, 0
 	beq	23f			/* skip if not */
+BEGIN_FTR_SECTION
+	ld	r3, HSTATE_MMCR(r13)
+	andi.	r4, r3, MMCR0_PMAO_SYNC | MMCR0_PMAO
+	cmpwi	r4, MMCR0_PMAO
+	beql	kvmppc_fix_pmao
+END_FTR_SECTION_IFSET(CPU_FTR_PMAO_BUG)
 	lwz	r3, HSTATE_PMC(r13)
 	lwz	r4, HSTATE_PMC + 4(r13)
 	lwz	r5, HSTATE_PMC + 8(r13)
@@ -726,6 +732,12 @@ skip_tm:
 	sldi	r3, r3, 31		/* MMCR0_FC (freeze counters) bit */
 	mtspr	SPRN_MMCR0, r3		/* freeze all counters, disable ints */
 	isync
+BEGIN_FTR_SECTION
+	ld	r3, VCPU_MMCR(r4)
+	andi.	r5, r3, MMCR0_PMAO_SYNC | MMCR0_PMAO
+	cmpwi	r5, MMCR0_PMAO
+	beql	kvmppc_fix_pmao
+END_FTR_SECTION_IFSET(CPU_FTR_PMAO_BUG)
 	lwz	r3, VCPU_PMC(r4)	/* always load up guest PMU registers */
 	lwz	r5, VCPU_PMC + 4(r4)	/* to prevent information leak */
 	lwz	r6, VCPU_PMC + 8(r4)
@@ -1324,6 +1336,30 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
 25:
 	/* Save PMU registers if requested */
 	/* r8 and cr0.eq are live here */
+BEGIN_FTR_SECTION
+	/*
+	 * POWER8 seems to have a hardware bug where setting
+	 * MMCR0[PMAE] along with MMCR0[PMC1CE] and/or MMCR0[PMCjCE]
+	 * when some counters are already negative doesn't seem
+	 * to cause a performance monitor alert (and hence interrupt).
+	 * The effect of this is that when saving the PMU state,
+	 * if there is no PMU alert pending when we read MMCR0
+	 * before freezing the counters, but one becomes pending
+	 * before we read the counters, we lose it.
+	 * To work around this, we need a way to freeze the counters
+	 * before reading MMCR0.  Normally, freezing the counters
+	 * is done by writing MMCR0 (to set MMCR0[FC]) which
+	 * unavoidably writes MMCR0[PMA0] as well.  On POWER8,
+	 * we can also freeze the counters using MMCR2, by writing
+	 * 1s to all the counter freeze condition bits (there are
+	 * 9 bits each for 6 counters).
+	 */
+	li	r3, -1			/* set all freeze bits */
+	clrrdi	r3, r3, 10
+	mfspr	r10, SPRN_MMCR2
+	mtspr	SPRN_MMCR2, r3
+	isync
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	li	r3, 1
 	sldi	r3, r3, 31		/* MMCR0_FC (freeze counters) bit */
 	mfspr	r4, SPRN_MMCR0		/* save MMCR0 */
@@ -1347,6 +1383,9 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
 	std	r4, VCPU_MMCR(r9)
 	std	r5, VCPU_MMCR + 8(r9)
 	std	r6, VCPU_MMCR + 16(r9)
+BEGIN_FTR_SECTION
+	std	r10, VCPU_MMCR + 24(r9)
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	std	r7, VCPU_SIAR(r9)
 	std	r8, VCPU_SDAR(r9)
 	mfspr	r3, SPRN_PMC1
@@ -1370,12 +1409,10 @@ BEGIN_FTR_SECTION
 	stw	r11, VCPU_PMC + 28(r9)
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201)
 BEGIN_FTR_SECTION
-	mfspr	r4, SPRN_MMCR2
 	mfspr	r5, SPRN_SIER
 	mfspr	r6, SPRN_SPMC1
 	mfspr	r7, SPRN_SPMC2
 	mfspr	r8, SPRN_MMCRS
-	std	r4, VCPU_MMCR + 24(r9)
 	std	r5, VCPU_SIER(r9)
 	stw	r6, VCPU_PMC + 24(r9)
 	stw	r7, VCPU_PMC + 28(r9)
@@ -2311,3 +2348,21 @@ kvmppc_msr_interrupt:
 	li	r0, 1
 1:	rldimi	r11, r0, MSR_TS_S_LG, 63 - MSR_TS_T_LG
 	blr
+
+/*
+ * This works around a hardware bug on POWER8E processors, where
+ * writing a 1 to the MMCR0[PMAO] bit doesn't generate a
+ * performance monitor interrupt.  Instead, when we need to have
+ * an interrupt pending, we have to arrange for a counter to overflow.
+ */
+kvmppc_fix_pmao:
+	li	r3, 0
+	mtspr	SPRN_MMCR2, r3
+	lis	r3, (MMCR0_PMXE | MMCR0_FCECE)@h
+	ori	r3, r3, MMCR0_PMCjCE | MMCR0_C56RUN
+	mtspr	SPRN_MMCR0, r3
+	lis	r3, 0x7fff
+	ori	r3, r3, 0xffff
+	mtspr	SPRN_PMC6, r3
+	isync
+	blr