@@ -96,6 +96,7 @@ struct kvmppc_vcore {
struct kvm_vcpu *runner;
struct kvm *kvm;
u64 tb_offset; /* guest timebase - host timebase */
+ u64 tb_offset_applied; /* timebase offset currently in force */
ulong lpcr;
u32 arch_compat;
ulong pcr;
@@ -562,6 +562,7 @@ int main(void)
OFFSET(VCORE_NAPPING_THREADS, kvmppc_vcore, napping_threads);
OFFSET(VCORE_KVM, kvmppc_vcore, kvm);
OFFSET(VCORE_TB_OFFSET, kvmppc_vcore, tb_offset);
+ OFFSET(VCORE_TB_OFFSET_APPL, kvmppc_vcore, tb_offset_applied);
OFFSET(VCORE_LPCR, kvmppc_vcore, lpcr);
OFFSET(VCORE_PCR, kvmppc_vcore, pcr);
OFFSET(VCORE_DPDES, kvmppc_vcore, dpdes);
@@ -2441,6 +2441,7 @@ static void init_vcore_to_run(struct kvmppc_vcore *vc)
vc->in_guest = 0;
vc->napping_threads = 0;
vc->conferring_threads = 0;
+ vc->tb_offset_applied = 0;
}
static bool can_dynamic_split(struct kvmppc_vcore *vc, struct core_info *cip)
@@ -692,6 +692,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
22: ld r8,VCORE_TB_OFFSET(r5)
cmpdi r8,0
beq 37f
+ std r8, VCORE_TB_OFFSET_APPL(r5)
mftb r6 /* current host timebase */
add r8,r8,r6
mtspr SPRN_TBU40,r8 /* update upper 40 bits */
@@ -940,18 +941,6 @@ FTR_SECTION_ELSE
ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
8:
- /*
- * Set the decrementer to the guest decrementer.
- */
- ld r8,VCPU_DEC_EXPIRES(r4)
- /* r8 is a host timebase value here, convert to guest TB */
- ld r5,HSTATE_KVM_VCORE(r13)
- ld r6,VCORE_TB_OFFSET(r5)
- add r8,r8,r6
- mftb r7
- subf r3,r7,r8
- mtspr SPRN_DEC,r3
-
ld r5, VCPU_SPRG0(r4)
ld r6, VCPU_SPRG1(r4)
ld r7, VCPU_SPRG2(r4)
@@ -1005,6 +994,18 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
mtspr SPRN_LPCR,r8
isync
+ /*
+ * Set the decrementer to the guest decrementer.
+ */
+ ld r8,VCPU_DEC_EXPIRES(r4)
+ /* r8 is a host timebase value here, convert to guest TB */
+ ld r5,HSTATE_KVM_VCORE(r13)
+ ld r6,VCORE_TB_OFFSET_APPL(r5)
+ add r8,r8,r6
+ mftb r7
+ subf r3,r7,r8
+ mtspr SPRN_DEC,r3
+
/* Check if HDEC expires soon */
mfspr r3, SPRN_HDEC
EXTEND_HDEC(r3)
@@ -1597,8 +1598,27 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
guest_bypass:
stw r12, STACK_SLOT_TRAP(r1)
- mr r3, r12
+
+ /* Save DEC */
+ /* Do this before kvmhv_commence_exit so we know TB is guest TB */
+ ld r3, HSTATE_KVM_VCORE(r13)
+ mfspr r5,SPRN_DEC
+ mftb r6
+ /* On P9, if the guest has large decr enabled, don't sign extend */
+BEGIN_FTR_SECTION
+ ld r4, VCORE_LPCR(r3)
+ andis. r4, r4, LPCR_LD@h
+ bne 16f
+END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
+ extsw r5,r5
+16: add r5,r5,r6
+ /* r5 is a guest timebase value here, convert to host TB */
+ ld r4,VCORE_TB_OFFSET_APPL(r3)
+ subf r5,r4,r5
+ std r5,VCPU_DEC_EXPIRES(r9)
+
/* Increment exit count, poke other threads to exit */
+ mr r3, r12
bl kvmhv_commence_exit
nop
ld r9, HSTATE_KVM_VCPU(r13)
@@ -1639,23 +1659,6 @@ guest_bypass:
mtspr SPRN_PURR,r3
mtspr SPRN_SPURR,r4
- /* Save DEC */
- ld r3, HSTATE_KVM_VCORE(r13)
- mfspr r5,SPRN_DEC
- mftb r6
- /* On P9, if the guest has large decr enabled, don't sign extend */
-BEGIN_FTR_SECTION
- ld r4, VCORE_LPCR(r3)
- andis. r4, r4, LPCR_LD@h
- bne 16f
-END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
- extsw r5,r5
-16: add r5,r5,r6
- /* r5 is a guest timebase value here, convert to host TB */
- ld r4,VCORE_TB_OFFSET(r3)
- subf r5,r4,r5
- std r5,VCPU_DEC_EXPIRES(r9)
-
BEGIN_FTR_SECTION
b 8f
END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
@@ -2017,9 +2020,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
27:
/* Subtract timebase offset from timebase */
- ld r8,VCORE_TB_OFFSET(r5)
+ ld r8, VCORE_TB_OFFSET_APPL(r5)
cmpdi r8,0
beq 17f
+ li r0, 0
+ std r0, VCORE_TB_OFFSET_APPL(r5)
mftb r6 /* current guest timebase */
subf r8,r8,r6
mtspr SPRN_TBU40,r8 /* update upper 40 bits */
@@ -2700,7 +2705,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
add r3, r3, r5
ld r4, HSTATE_KVM_VCPU(r13)
ld r5, HSTATE_KVM_VCORE(r13)
- ld r6, VCORE_TB_OFFSET(r5)
+ ld r6, VCORE_TB_OFFSET_APPL(r5)
subf r3, r6, r3 /* convert to host TB value */
std r3, VCPU_DEC_EXPIRES(r4)
@@ -2799,7 +2804,7 @@ END_FTR_SECTION(CPU_FTR_TM | CPU_FTR_P9_TM_HV_ASSIST, 0)
/* Restore guest decrementer */
ld r3, VCPU_DEC_EXPIRES(r4)
ld r5, HSTATE_KVM_VCORE(r13)
- ld r6, VCORE_TB_OFFSET(r5)
+ ld r6, VCORE_TB_OFFSET_APPL(r5)
add r3, r3, r6 /* convert host TB to guest TB value */
mftb r7
subf r3, r7, r3
@@ -3606,12 +3611,9 @@ kvmppc_fix_pmao:
*/
kvmhv_start_timing:
ld r5, HSTATE_KVM_VCORE(r13)
- lbz r6, VCORE_IN_GUEST(r5)
- cmpwi r6, 0
- beq 5f /* if in guest, need to */
- ld r6, VCORE_TB_OFFSET(r5) /* subtract timebase offset */
-5: mftb r5
- subf r5, r6, r5
+ ld r6, VCORE_TB_OFFSET_APPL(r5)
+ mftb r5
+ subf r5, r6, r5 /* subtract current timebase offset */
std r3, VCPU_CUR_ACTIVITY(r4)
std r5, VCPU_ACTIVITY_START(r4)
blr
@@ -3622,15 +3624,12 @@ kvmhv_start_timing:
*/
kvmhv_accumulate_time:
ld r5, HSTATE_KVM_VCORE(r13)
- lbz r8, VCORE_IN_GUEST(r5)
- cmpwi r8, 0
- beq 4f /* if in guest, need to */
- ld r8, VCORE_TB_OFFSET(r5) /* subtract timebase offset */
-4: ld r5, VCPU_CUR_ACTIVITY(r4)
+ ld r8, VCORE_TB_OFFSET_APPL(r5)
+ ld r5, VCPU_CUR_ACTIVITY(r4)
ld r6, VCPU_ACTIVITY_START(r4)
std r3, VCPU_CUR_ACTIVITY(r4)
mftb r7
- subf r7, r8, r7
+ subf r7, r8, r7 /* subtract current timebase offset */
std r7, VCPU_ACTIVITY_START(r4)
cmpdi r5, 0
beqlr
Currently, the HV KVM guest entry/exit code adds the timebase offset from the vcore struct to the timebase on guest entry, and subtracts it on guest exit. Which is fine, except that it is possible for userspace to change the offset using the SET_ONE_REG interface while the vcore is running, as there is only one timebase offset per vcore but potentially multiple VCPUs in the vcore. If that were to happen, KVM would subtract a different offset on guest exit from that which it had added on guest entry, leading to the timebase being out of sync between cores in the host, which then leads to bad things happening such as hangs and spurious watchdog timeouts. To fix this, we add a new field 'tb_offset_applied' to the vcore struct which stores the offset that is currently applied to the timebase. This value is set from the vcore tb_offset field on guest entry, and is what is subtracted from the timebase on guest exit. Since it is zero when the timebase offset is not applied, we can simplify the logic in kvmhv_start_timing and kvmhv_accumulate_time. In addition, we had secondary threads reading the timebase while running concurrently with code on the primary thread which would eventually add or subtract the timebase offset from the timebase. This occurred while saving or restoring the DEC register value on the secondary threads. Although no specific incorrect behaviour has been observed, this is a race which should be fixed. To fix it, we move the DEC saving code to just before we call kvmhv_commence_exit, and the DEC restoring code to after the point where we have waited for the primary thread to switch the MMU context and add the timebase offset. That way we are sure that the timebase contains the guest timebase value in both cases. Signed-off-by: Paul Mackerras <paulus@ozlabs.org> --- arch/powerpc/include/asm/kvm_book3s.h | 1 + arch/powerpc/kernel/asm-offsets.c | 1 + arch/powerpc/kvm/book3s_hv.c | 1 + arch/powerpc/kvm/book3s_hv_rmhandlers.S | 89 ++++++++++++++++----------------- 4 files changed, 47 insertions(+), 45 deletions(-)