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Commit 91648ec0 authored by pingfan liu's avatar pingfan liu Committed by Alexander Graf
Browse files

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: default avatarLiu Ping Fan <pingfank@linux.vnet.ibm.com>
Reviewed-by: default avatarPaul Mackerras <paulus@samba.org>
CC: stable@vger.kernel.org
Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
parent c9438092

arch/powerpc/kvm/book3s_64_mmu_hv.c

+5 −1
Original line number Diff line number Diff line
@@ -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);

arch/powerpc/kvm/book3s_hv_rm_mmu.c

+4 −0
Original line number Diff line number Diff line
@@ -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)

{