3.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: pingfan liu <qemul...@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 <pingf...@linux.vnet.ibm.com>
Reviewed-by: Paul Mackerras <pau...@samba.org>
Signed-off-by: Alexander Graf <ag...@suse.de>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
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(-)
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -393,11 +393,14 @@ static int kvmppc_mmu_book3s_64_hv_xlate
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;
@@ -405,6 +408,7 @@ static int kvmppc_mmu_book3s_64_hv_xlate
/* 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);
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -649,6 +649,10 @@ 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)
{
--
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