4.20-stable review patch. If anyone has any objections, please let me know.
------------------
From: Paul Mackerras <paulus@xxxxxxxxxx>
commit 234ff0b729ad882d20f7996591a964965647addf upstream.
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@xxxxxxxxxxxxxxx # v4.15+
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/kvm/book3s_64_mmu_hv.c | 3 +++
arch/powerpc/kvm/book3s_hv.c | 17 +++++++++++------
2 files changed, 14 insertions(+), 6 deletions(-)
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -743,12 +743,15 @@ 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);
}
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4532,12 +4532,15 @@ int kvmppc_switch_mmu_to_hpt(struct kvm
{
if (nesting_enabled(kvm))
kvmhv_release_all_nested(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;
}
@@ -4549,12 +4552,14 @@ int kvmppc_switch_mmu_to_radix(struct kv
err = kvmppc_init_vm_radix(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);
- kvmppc_rmap_reset(kvm);
- kvm->arch.radix = 1;
return 0;
}
