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KVM: PPC: Book3S HV: Fix race between kvm_unmap_hva_range and MMU mode switch 

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: 18c3640cef ("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>
This commit is contained in:
Paul Mackerras 2018-11-16 21:28:18 +11:00
parent fd65d3142f
commit 234ff0b729
2 changed files with 14 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/powerpc/kvm/book3s_64_mmu_hv.c
View File

@ -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);
}

17
arch/powerpc/kvm/book3s_hv.c
View File

@ -4532,12 +4532,15 @@ int kvmppc_switch_mmu_to_hpt(struct kvm *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 kvm *kvm)
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;
}