diff options
| author | Paul Mackerras <paulus@samba.org> | 2013-11-16 17:46:03 +1100 |
|---|---|---|
| committer | Alexander Graf <agraf@suse.de> | 2013-11-18 22:38:30 +0100 |
| commit | f019b7ad76e6bdbc8462cbe17ad5b86a25fcdf24 (patch) | |
| tree | 03a6ed2ce877bb17576ac8337305828d16b8a3bc /arch | |
| parent | caaa4c804fae7bb654f7d00b35b8583280a9c52c (diff) | |
| download | linux-0-day-f019b7ad76e6bdbc8462cbe17ad5b86a25fcdf24.tar.gz linux-0-day-f019b7ad76e6bdbc8462cbe17ad5b86a25fcdf24.tar.xz | |
KVM: PPC: Book3S HV: Refine barriers in guest entry/exit
Some users have reported instances of the host hanging with secondary
threads of a core waiting for the primary thread to exit the guest,
and the primary thread stuck in nap mode. This prompted a review of
the memory barriers in the guest entry/exit code, and this is the
result. Most of these changes are the suggestions of Dean Burdick
<deanburdick@us.ibm.com>.
The barriers between updating napping_threads and reading the
entry_exit_count on the one hand, and updating entry_exit_count and
reading napping_threads on the other, need to be isync not lwsync,
since we need to ensure that either the napping_threads update or the
entry_exit_count update get seen. It is not sufficient to order the
load vs. lwarx, as lwsync does; we need to order the load vs. the
stwcx., so we need isync.
In addition, we need a full sync before sending IPIs to wake other
threads from nap, to ensure that the write to the entry_exit_count is
visible before the IPI occurs.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/powerpc/kvm/book3s_hv_rmhandlers.S | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S index bc8de75b1925c..bde28da696103 100644 --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S @@ -153,7 +153,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206) 13: b machine_check_fwnmi - /* * We come in here when wakened from nap mode on a secondary hw thread. * Relocation is off and most register values are lost. @@ -224,6 +223,11 @@ kvm_start_guest: /* Clear our vcpu pointer so we don't come back in early */ li r0, 0 std r0, HSTATE_KVM_VCPU(r13) + /* + * Make sure we clear HSTATE_KVM_VCPU(r13) before incrementing + * the nap_count, because once the increment to nap_count is + * visible we could be given another vcpu. + */ lwsync /* Clear any pending IPI - we're an offline thread */ ld r5, HSTATE_XICS_PHYS(r13) @@ -241,7 +245,6 @@ kvm_start_guest: /* increment the nap count and then go to nap mode */ ld r4, HSTATE_KVM_VCORE(r13) addi r4, r4, VCORE_NAP_COUNT - lwsync /* make previous updates visible */ 51: lwarx r3, 0, r4 addi r3, r3, 1 stwcx. r3, 0, r4 @@ -990,14 +993,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201) */ /* Increment the threads-exiting-guest count in the 0xff00 bits of vcore->entry_exit_count */ - lwsync ld r5,HSTATE_KVM_VCORE(r13) addi r6,r5,VCORE_ENTRY_EXIT 41: lwarx r3,0,r6 addi r0,r3,0x100 stwcx. r0,0,r6 bne 41b - lwsync + isync /* order stwcx. vs. reading napping_threads */ /* * At this point we have an interrupt that we have to pass @@ -1030,6 +1032,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201) sld r0,r0,r4 andc. r3,r3,r0 /* no sense IPI'ing ourselves */ beq 43f + /* Order entry/exit update vs. IPIs */ + sync mulli r4,r4,PACA_SIZE /* get paca for thread 0 */ subf r6,r4,r13 42: andi. r0,r3,1 @@ -1638,10 +1642,10 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_206) bge kvm_cede_exit stwcx. r4,0,r6 bne 31b + /* order napping_threads update vs testing entry_exit_count */ + isync li r0,1 stb r0,HSTATE_NAPPING(r13) - /* order napping_threads update vs testing entry_exit_count */ - lwsync mr r4,r3 lwz r7,VCORE_ENTRY_EXIT(r5) cmpwi r7,0x100 |