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powerpc: kvm: fix rare but potential deadlock scene 

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>
CC: stable@vger.kernel.org
Signed-off-by: Alexander Graf <agraf@suse.de>
This commit is contained in:
pingfan liu 2013-11-15 16:35:00 +08:00 committed by Alexander Graf
parent c9438092ca
commit 91648ec09c
2 changed files with 9 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/powerpc/kvm/book3s_64_mmu_hv.c
View File

@ -469,11 +469,14 @@ 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;
@ -481,6 +484,7 @@ 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);

4
arch/powerpc/kvm/book3s_hv_rm_mmu.c
View File

@ -749,6 +749,10 @@ 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)
{