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@xxxxxxxxxxxxxxxxxx>
---
arch/powerpc/include/asm/kvm_book3s.h | 4 ++--
arch/powerpc/kvm/book3s_64_mmu_hv.c | 5 +++--
arch/powerpc/kvm/book3s_hv_rm_mmu.c | 20 ++++++++++++++++----
3 files changed, 21 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
index a818932..3d710ba 100644
--- a/arch/powerpc/include/asm/kvm_book3s.h
+++ b/arch/powerpc/include/asm/kvm_book3s.h
@@ -129,9 +129,9 @@ extern void kvmppc_mmu_flush_segments(struct kvm_vcpu *vcpu);
extern int kvmppc_book3s_hv_page_fault(struct kvm_run *run,
struct kvm_vcpu *vcpu, unsigned long addr,
unsigned long status);
-extern void kvmppc_hv_unlock_hpte(ulong *hptep, ulong *hpte_val);
+extern void kvmppc_hv_unlock_hpte(ulong *hptep, ulong *hpte_val, bool vmode);
extern long kvmppc_hv_find_lock_hpte(struct kvm *kvm, gva_t eaddr,
- unsigned long slb_v, unsigned long valid);
+ unsigned long slb_v, unsigned long valid, bool vmode);
extern void kvmppc_mmu_hpte_cache_map(struct kvm_vcpu *vcpu, struct hpte_cache *pte);
extern struct hpte_cache *kvmppc_mmu_hpte_cache_next(struct kvm_vcpu *vcpu);
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 97685e7..12d9635 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -475,13 +475,14 @@ static int kvmppc_mmu_book3s_64_hv_xlate(struct kvm_vcpu *vcpu, gva_t eaddr,
/* Find the HPTE in the hash table */
index = kvmppc_hv_find_lock_hpte(kvm, eaddr, slb_v,
- HPTE_V_VALID | HPTE_V_ABSENT);
+ HPTE_V_VALID | HPTE_V_ABSENT,
+ true);
if (index < 0)
return -ENOENT;
hptep = (unsigned long *)(kvm->arch.hpt_virt + (index << 4));
v = hptep[0];
gr = kvm->arch.revmap[index].guest_rpte;
- kvmppc_hv_unlock_hpte(hptep, &v);
+ kvmppc_hv_unlock_hpte(hptep, &v, true);
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 0ff9e91..18a9425 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -749,16 +749,22 @@ static int slb_base_page_shift[4] = {
20, /* 1M, unsupported */
};
-void kvmppc_hv_unlock_hpte(unsigned long *hptep, unsigned long *hpte_val)
+void kvmppc_hv_unlock_hpte(unsigned long *hptep, unsigned long *hpte_val,
+ bool vmode)
{
*hpte_val = *hpte_val & ~HPTE_V_HVLOCK;
asm volatile("lwsync" : : : "memory");
*hptep = *hpte_val;
+ if (unlikely(vmode))
+ preempt_enable();
}
EXPORT_SYMBOL(kvmppc_hv_unlock_hpte);
+/* If called from virtmode and success to lock, then the context will be set
+ * as preemption disabled
+ */
long kvmppc_hv_find_lock_hpte(struct kvm *kvm, gva_t eaddr, unsigned long slb_v,
- unsigned long valid)
+ unsigned long valid, bool vmode)
{
unsigned int i;
unsigned int pshift;
@@ -796,6 +802,9 @@ long kvmppc_hv_find_lock_hpte(struct kvm *kvm, gva_t eaddr, unsigned long slb_v,
avpn &= ~0x7fUL;
val |= avpn;
+ if (unlikely(vmode))
+ preempt_disable();
+
for (;;) {
hpte = (unsigned long *)(kvm->arch.hpt_virt + (hash << 7));
@@ -833,6 +842,9 @@ long kvmppc_hv_find_lock_hpte(struct kvm *kvm, gva_t eaddr, unsigned long slb_v,
val |= HPTE_V_SECONDARY;
hash = hash ^ kvm->arch.hpt_mask;
}
+
+ if (unlikely(vmode))
+ preempt_enable();
return -1;
}
EXPORT_SYMBOL(kvmppc_hv_find_lock_hpte);
@@ -864,7 +876,7 @@ long kvmppc_hpte_hv_fault(struct kvm_vcpu *vcpu, unsigned long addr,
if (status & DSISR_NOHPTE)
valid |= HPTE_V_ABSENT;
- index = kvmppc_hv_find_lock_hpte(kvm, addr, slb_v, valid);
+ index = kvmppc_hv_find_lock_hpte(kvm, addr, slb_v, valid, false);
if (index < 0) {
if (status & DSISR_NOHPTE)
return status; /* there really was no HPTE */
@@ -875,7 +887,7 @@ long kvmppc_hpte_hv_fault(struct kvm_vcpu *vcpu, unsigned long addr,
r = hpte[1];
rev = real_vmalloc_addr(&kvm->arch.revmap[index]);
gr = rev->guest_rpte;
- kvmppc_hv_unlock_hpte(hpte, &v);
+ kvmppc_hv_unlock_hpte(hpte, &v, false);
/* For not found, if the HPTE is valid by now, retry the instruction */
if ((status & DSISR_NOHPTE) && (v & HPTE_V_VALID))
--
1.8.1.4
--
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