From: Paul Mackerras paulus@ozlabs.org
[ Upstream commit 234ff0b729ad882d20f7996591a964965647addf ]
Testing has revealed an occasional crash which appears to be caused by a race between kvmppc_switch_mmu_to_hpt and kvm_unmap_hva_range_hv. The symptom is a NULL pointer dereference in __find_linux_pte() called from kvm_unmap_radix() with kvm->arch.pgtable == NULL.
Looking at kvmppc_switch_mmu_to_hpt(), it does indeed clear kvm->arch.pgtable (via kvmppc_free_radix()) before setting kvm->arch.radix to NULL, and there is nothing to prevent kvm_unmap_hva_range_hv() or the other MMU callback functions from being called concurrently with kvmppc_switch_mmu_to_hpt() or kvmppc_switch_mmu_to_radix().
This patch therefore adds calls to spin_lock/unlock on the kvm->mmu_lock around the assignments to kvm->arch.radix, and makes sure that the partition-scoped radix tree or HPT is only freed after changing kvm->arch.radix.
This also takes the kvm->mmu_lock in kvmppc_rmap_reset() to make sure that the clearing of each rmap array (one per memslot) doesn't happen concurrently with use of the array in the kvm_unmap_hva_range_hv() or the other MMU callbacks.
Fixes: 18c3640cefc7 ("KVM: PPC: Book3S HV: Add infrastructure for running HPT guests on radix host") Cc: stable@vger.kernel.org # v4.15+ Signed-off-by: Paul Mackerras paulus@ozlabs.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kvm/book3s_64_mmu_hv.c | 3 +++ arch/powerpc/kvm/book3s_hv.c | 15 +++++++++++---- 2 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c index 68e14afecac85..a488c105b9234 100644 --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c @@ -744,12 +744,15 @@ void kvmppc_rmap_reset(struct kvm *kvm) srcu_idx = srcu_read_lock(&kvm->srcu); slots = kvm_memslots(kvm); kvm_for_each_memslot(memslot, slots) { + /* Mutual exclusion with kvm_unmap_hva_range etc. */ + spin_lock(&kvm->mmu_lock); /* * This assumes it is acceptable to lose reference and * change bits across a reset. */ memset(memslot->arch.rmap, 0, memslot->npages * sizeof(*memslot->arch.rmap)); + spin_unlock(&kvm->mmu_lock); } srcu_read_unlock(&kvm->srcu, srcu_idx); } diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 083dcedba11ce..9595db30e6b87 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -3813,12 +3813,15 @@ static int kvmppc_hv_setup_htab_rma(struct kvm_vcpu *vcpu) /* Must be called with kvm->lock held and mmu_ready = 0 and no vcpus running */ int kvmppc_switch_mmu_to_hpt(struct kvm *kvm) { + kvmppc_rmap_reset(kvm); + kvm->arch.process_table = 0; + /* Mutual exclusion with kvm_unmap_hva_range etc. */ + spin_lock(&kvm->mmu_lock); + kvm->arch.radix = 0; + spin_unlock(&kvm->mmu_lock); kvmppc_free_radix(kvm); kvmppc_update_lpcr(kvm, LPCR_VPM1, LPCR_VPM1 | LPCR_UPRT | LPCR_GTSE | LPCR_HR); - kvmppc_rmap_reset(kvm); - kvm->arch.radix = 0; - kvm->arch.process_table = 0; return 0; }
@@ -3831,10 +3834,14 @@ int kvmppc_switch_mmu_to_radix(struct kvm *kvm) if (err) return err;
+ kvmppc_rmap_reset(kvm); + /* Mutual exclusion with kvm_unmap_hva_range etc. */ + spin_lock(&kvm->mmu_lock); + kvm->arch.radix = 1; + spin_unlock(&kvm->mmu_lock); kvmppc_free_hpt(&kvm->arch.hpt); kvmppc_update_lpcr(kvm, LPCR_UPRT | LPCR_GTSE | LPCR_HR, LPCR_VPM1 | LPCR_UPRT | LPCR_GTSE | LPCR_HR); - kvm->arch.radix = 1; return 0; }