[PATCH 49/56] KVM: PPC: Work around POWER7 DABR corruption problem

Alexander Graf
2012-03-15T12:11:18Z

From: Paul Mackerras <paulus@samba.org>

It turns out that on POWER7, writing to the DABR can cause a corrupted
value to be written if the PMU is active and updating SDAR in continuous
sampling mode. To work around this, we make sure that the PMU is inactive
and SDAR updates are disabled (via MMCRA) when we are context-switching
DABR.

When the guest sets DABR via the H_SET_DABR hypercall, we use a slightly
different workaround, which is to read back the DABR and write it again
if it got corrupted.

While we are at it, make it consistent that the saving and restoring
of the guest's non-volatile GPRs and the FPRs are done with the guest
setup of the PMU active.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
---
arch/powerpc/kvm/book3s_hv_interrupts.S | 9 ++-
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 93 ++++++++++++++++++-------------
2 files changed, 61 insertions(+), 41 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_interrupts.S b/arch/powerpc/kvm/book3s_hv_interrupts.S
index d3fb4df..84035a5 100644
--- a/arch/powerpc/kvm/book3s_hv_interrupts.S
+++ b/arch/powerpc/kvm/book3s_hv_interrupts.S
@@ -68,19 +68,24 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
rotldi r10,r10,16
mtmsrd r10,1

- /* Save host PMU registers and load guest PMU registers */
+ /* Save host PMU registers */
/* R4 is live here (vcpu pointer) but not r3 or r5 */
li r3, 1
sldi r3, r3, 31 /* MMCR0_FC (freeze counters) bit */
mfspr r7, SPRN_MMCR0 /* save MMCR0 */
mtspr SPRN_MMCR0, r3 /* freeze all counters, disable interrupts */
+ mfspr r6, SPRN_MMCRA
+BEGIN_FTR_SECTION
+ /* On P7, clear MMCRA in order to disable SDAR updates */
+ li r5, 0
+ mtspr SPRN_MMCRA, r5
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
isync
ld r3, PACALPPACAPTR(r13) /* is the host using the PMU? */
lbz r5, LPPACA_PMCINUSE(r3)
cmpwi r5, 0
beq 31f /* skip if not */
mfspr r5, SPRN_MMCR1
- mfspr r6, SPRN_MMCRA
std r7, HSTATE_MMCR(r13)
std r5, HSTATE_MMCR + 8(r13)
std r6, HSTATE_MMCR + 16(r13)
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index d595033..a84aafc 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -159,24 +159,15 @@ kvmppc_hv_entry:
mflr r0
std r0, HSTATE_VMHANDLER(r13)

- ld r14, VCPU_GPR(r14)(r4)
- ld r15, VCPU_GPR(r15)(r4)
- ld r16, VCPU_GPR(r16)(r4)
- ld r17, VCPU_GPR(r17)(r4)
- ld r18, VCPU_GPR(r18)(r4)
- ld r19, VCPU_GPR(r19)(r4)
- ld r20, VCPU_GPR(r20)(r4)
- ld r21, VCPU_GPR(r21)(r4)
- ld r22, VCPU_GPR(r22)(r4)
- ld r23, VCPU_GPR(r23)(r4)
- ld r24, VCPU_GPR(r24)(r4)
- ld r25, VCPU_GPR(r25)(r4)
- ld r26, VCPU_GPR(r26)(r4)
- ld r27, VCPU_GPR(r27)(r4)
- ld r28, VCPU_GPR(r28)(r4)
- ld r29, VCPU_GPR(r29)(r4)
- ld r30, VCPU_GPR(r30)(r4)
- ld r31, VCPU_GPR(r31)(r4)
+ /* Set partition DABR */
+ /* Do this before re-enabling PMU to avoid P7 DABR corruption bug */
+ li r5,3
+ ld r6,VCPU_DABR(r4)
+ mtspr SPRN_DABRX,r5
+ mtspr SPRN_DABR,r6
+BEGIN_FTR_SECTION
+ isync
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)

/* Load guest PMU registers */
/* R4 is live here (vcpu pointer) */
@@ -215,6 +206,25 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201)
/* Load up FP, VMX and VSX registers */
bl kvmppc_load_fp

+ ld r14, VCPU_GPR(r14)(r4)
+ ld r15, VCPU_GPR(r15)(r4)
+ ld r16, VCPU_GPR(r16)(r4)
+ ld r17, VCPU_GPR(r17)(r4)
+ ld r18, VCPU_GPR(r18)(r4)
+ ld r19, VCPU_GPR(r19)(r4)
+ ld r20, VCPU_GPR(r20)(r4)
+ ld r21, VCPU_GPR(r21)(r4)
+ ld r22, VCPU_GPR(r22)(r4)
+ ld r23, VCPU_GPR(r23)(r4)
+ ld r24, VCPU_GPR(r24)(r4)
+ ld r25, VCPU_GPR(r25)(r4)
+ ld r26, VCPU_GPR(r26)(r4)
+ ld r27, VCPU_GPR(r27)(r4)
+ ld r28, VCPU_GPR(r28)(r4)
+ ld r29, VCPU_GPR(r29)(r4)
+ ld r30, VCPU_GPR(r30)(r4)
+ ld r31, VCPU_GPR(r31)(r4)
+
BEGIN_FTR_SECTION
/* Switch DSCR to guest value */
ld r5, VCPU_DSCR(r4)
@@ -256,12 +266,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
mtspr SPRN_DAR, r5
mtspr SPRN_DSISR, r6

- /* Set partition DABR */
- li r5,3
- ld r6,VCPU_DABR(r4)
- mtspr SPRN_DABRX,r5
- mtspr SPRN_DABR,r6
-
BEGIN_FTR_SECTION
/* Restore AMR and UAMOR, set AMOR to all 1s */
ld r5,VCPU_AMR(r4)
@@ -955,12 +959,6 @@ BEGIN_FTR_SECTION
mtspr SPRN_AMR,r6
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)

- /* Restore host DABR and DABRX */
- ld r5,HSTATE_DABR(r13)
- li r6,7
- mtspr SPRN_DABR,r5
- mtspr SPRN_DABRX,r6
-
/* Switch DSCR back to host value */
BEGIN_FTR_SECTION
mfspr r8, SPRN_DSCR
@@ -999,6 +997,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
std r5, VCPU_SPRG2(r9)
std r6, VCPU_SPRG3(r9)

+ /* save FP state */
+ mr r3, r9
+ bl .kvmppc_save_fp
+
/* Increment yield count if they have a VPA */
ld r8, VCPU_VPA(r9) /* do they have a VPA? */
cmpdi r8, 0
@@ -1013,6 +1015,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
sldi r3, r3, 31 /* MMCR0_FC (freeze counters) bit */
mfspr r4, SPRN_MMCR0 /* save MMCR0 */
mtspr SPRN_MMCR0, r3 /* freeze all counters, disable ints */
+ mfspr r6, SPRN_MMCRA
+BEGIN_FTR_SECTION
+ /* On P7, clear MMCRA in order to disable SDAR updates */
+ li r7, 0
+ mtspr SPRN_MMCRA, r7
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
isync
beq 21f /* if no VPA, save PMU stuff anyway */
lbz r7, LPPACA_PMCINUSE(r8)
@@ -1021,7 +1029,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
std r3, VCPU_MMCR(r9) /* if not, set saved MMCR0 to FC */
b 22f
21: mfspr r5, SPRN_MMCR1
- mfspr r6, SPRN_MMCRA
std r4, VCPU_MMCR(r9)
std r5, VCPU_MMCR + 8(r9)
std r6, VCPU_MMCR + 16(r9)
@@ -1046,17 +1053,20 @@ BEGIN_FTR_SECTION
stw r11, VCPU_PMC + 28(r9)
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201)
22:
- /* save FP state */
- mr r3, r9
- bl .kvmppc_save_fp

/* Secondary threads go off to take a nap on POWER7 */
BEGIN_FTR_SECTION
- lwz r0,VCPU_PTID(r3)
+ lwz r0,VCPU_PTID(r9)
cmpwi r0,0
bne secondary_nap
END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)

+ /* Restore host DABR and DABRX */
+ ld r5,HSTATE_DABR(r13)
+ li r6,7
+ mtspr SPRN_DABR,r5
+ mtspr SPRN_DABRX,r6
+
/*
* Reload DEC. HDEC interrupts were disabled when
* we reloaded the host's LPCR value.
@@ -1393,7 +1403,12 @@ bounce_ext_interrupt:

_GLOBAL(kvmppc_h_set_dabr)
std r4,VCPU_DABR(r3)
- mtspr SPRN_DABR,r4
+ /* Work around P7 bug where DABR can get corrupted on mtspr */
+1: mtspr SPRN_DABR,r4
+ mfspr r5, SPRN_DABR
+ cmpd r4, r5
+ bne 1b
+ isync
li r3,0
blr

@@ -1615,8 +1630,8 @@ kvm_no_guest:
* r3 = vcpu pointer
*/
_GLOBAL(kvmppc_save_fp)
- mfmsr r9
- ori r8,r9,MSR_FP
+ mfmsr r5
+ ori r8,r5,MSR_FP
#ifdef CONFIG_ALTIVEC
BEGIN_FTR_SECTION
oris r8,r8,MSR_VEC@h
@@ -1665,7 +1680,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
#endif
mfspr r6,SPRN_VRSAVE
stw r6,VCPU_VRSAVE(r3)
- mtmsrd r9
+ mtmsrd r5
isync
blr

--
1.6.0.2