Messages in this thread Patch in this message | | | From | Kamal Mostafa <> | Subject | [PATCH 3.8 058/166] powerpc: kvm: fix rare but potential deadlock scene | Date | Wed, 15 Jan 2014 13:51:12 -0800 |
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3.8.13.16 -stable review patch. If anyone has any objections, please let me know.
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From: pingfan liu <qemulist@gmail.com>
commit 91648ec09c1ef69c4d840ab6dab391bfb452d554 upstream.
Since kvmppc_hv_find_lock_hpte() is called from both virtmode and realmode, so it can trigger the deadlock.
Suppose the following scene:
Two physical cpuM, cpuN, two VM instances A, B, each VM has a group of vcpus.
If on cpuM, vcpu_A_1 holds bitlock X (HPTE_V_HVLOCK), then is switched out, and on cpuN, vcpu_A_2 try to lock X in realmode, then cpuN will be caught in realmode for a long time.
What makes things even worse if the following happens, On cpuM, bitlockX is hold, on cpuN, Y is hold. vcpu_B_2 try to lock Y on cpuM in realmode vcpu_A_2 try to lock X on cpuN in realmode
Oops! deadlock happens
Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com> Reviewed-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Alexander Graf <agraf@suse.de> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- arch/powerpc/kvm/book3s_64_mmu_hv.c | 6 +++++- arch/powerpc/kvm/book3s_hv_rm_mmu.c | 4 ++++ 2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c index 8cc18ab..61a1dbf 100644 --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c @@ -473,11 +473,14 @@ static int kvmppc_mmu_book3s_64_hv_xlate(struct kvm_vcpu *vcpu, gva_t eaddr, slb_v = vcpu->kvm->arch.vrma_slb_v; } + preempt_disable(); /* Find the HPTE in the hash table */ index = kvmppc_hv_find_lock_hpte(kvm, eaddr, slb_v, HPTE_V_VALID | HPTE_V_ABSENT); - if (index < 0) + if (index < 0) { + preempt_enable(); return -ENOENT; + } hptep = (unsigned long *)(kvm->arch.hpt_virt + (index << 4)); v = hptep[0] & ~HPTE_V_HVLOCK; gr = kvm->arch.revmap[index].guest_rpte; @@ -485,6 +488,7 @@ static int kvmppc_mmu_book3s_64_hv_xlate(struct kvm_vcpu *vcpu, gva_t eaddr, /* Unlock the HPTE */ asm volatile("lwsync" : : : "memory"); hptep[0] = v; + preempt_enable(); gpte->eaddr = eaddr; gpte->vpage = ((v & HPTE_V_AVPN) << 4) | ((eaddr >> 12) & 0xfff); diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c index 19c93ba..9a1f990 100644 --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c @@ -735,6 +735,10 @@ static int slb_base_page_shift[4] = { 20, /* 1M, unsupported */ }; +/* When called from virtmode, this func should be protected by + * preempt_disable(), otherwise, the holding of HPTE_V_HVLOCK + * can trigger deadlock issue. + */ long kvmppc_hv_find_lock_hpte(struct kvm *kvm, gva_t eaddr, unsigned long slb_v, unsigned long valid) { -- 1.8.3.2
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