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authorPaul Mackerras <paulus@ozlabs.org>2018-10-04 14:51:11 +1000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-10-18 09:18:20 +0200
commit4a15f8a1de5912592045af0d30d1800f866837e3 (patch)
tree1815be86236d4ce9e7fcc56c400f444a3fc15906
parent726c11216e33f06762349153a0f4e0111dce869b (diff)
KVM: PPC: Book3S HV: Avoid crash from THP collapse during radix page fault
commit 6579804c431712d56956a63b1a01509441cc6800 upstream. Commit 71d29f43b633 ("KVM: PPC: Book3S HV: Don't use compound_order to determine host mapping size", 2018-09-11) added a call to __find_linux_pte() and a dereference of the returned PTE pointer to the radix page fault path in the common case where the page is normal system memory. Previously, __find_linux_pte() was only called for mappings to physical addresses which don't have a page struct (e.g. memory-mapped I/O) or where the page struct is marked as reserved memory. This exposes us to the possibility that the returned PTE pointer could be NULL, for example in the case of a concurrent THP collapse operation. Dereferencing the returned NULL pointer causes a host crash. To fix this, we check for NULL, and if it is NULL, we retry the operation by returning to the guest, with the expectation that it will generate the same page fault again (unless of course it has been fixed up by another CPU in the meantime). Fixes: 71d29f43b633 ("KVM: PPC: Book3S HV: Don't use compound_order to determine host mapping size") Signed-off-by: Paul Mackerras <paulus@ozlabs.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/powerpc/kvm/book3s_64_mmu_radix.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index ae023d2256ef..26d927bf2fdb 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -659,6 +659,16 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
*/
local_irq_disable();
ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift);
+ /*
+ * If the PTE disappeared temporarily due to a THP
+ * collapse, just return and let the guest try again.
+ */
+ if (!ptep) {
+ local_irq_enable();
+ if (page)
+ put_page(page);
+ return RESUME_GUEST;
+ }
pte = *ptep;
local_irq_enable();