On 4/16/20 7:03 AM, Paul Mackerras wrote: > Since cd758a9b57ee "KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot in HPT > page fault handler", it's been possible in fairly rare circumstances to > load a non-present PTE in kvmppc_book3s_hv_page_fault() when running a > guest on a POWER8 host. > > Because that case wasn't checked for, we could misinterpret the non-present > PTE as being a cache-inhibited PTE. That could mismatch with the > corresponding hash PTE, which would cause the function to fail with -EFAULT > a little further down. That would propagate up to the KVM_RUN ioctl() > generally causing the KVM userspace (usually qemu) to fall over. > > This addresses the problem by catching that case and returning to the guest > instead, letting it fault again, and retrying the whole page fault from > the beginning. > > For completeness, this fixes the radix page fault handler in the same > way. For radix this didn't cause any obvious misbehaviour, because we > ended up putting the non-present PTE into the guest's partition-scoped > page tables, leading immediately to another hypervisor data/instruction > storage interrupt, which would go through the page fault path again > and fix things up. > > Fixes: cd758a9b57ee "KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot in HPT page fault handler" > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1820402 > Reported-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx> I didn't see the reported issue with the current 5.7-rc1. Anyhow I gave this patch a try on a P8 host and a P9 host with a radix guest and a hash guest (using rhel6). Passthrough is fine also. Tested-by: Cédric Le Goater <clg@xxxxxxxx> The code looks correct, Reviewed-by: Cédric Le Goater <clg@xxxxxxxx> Thanks, C. > --- > This is a reworked version of the patch David Gibson sent recently, > with the fix applied to the radix case as well. The commit message > is mostly stolen from David's patch. > > arch/powerpc/kvm/book3s_64_mmu_hv.c | 9 +++++---- > arch/powerpc/kvm/book3s_64_mmu_radix.c | 9 +++++---- > 2 files changed, 10 insertions(+), 8 deletions(-) > > diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c > index 3aecec8..20b7dce 100644 > --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c > +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c > @@ -604,18 +604,19 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu, > */ > local_irq_disable(); > ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift); > + pte = __pte(0); > + if (ptep) > + pte = *ptep; > + local_irq_enable(); > /* > * If the PTE disappeared temporarily due to a THP > * collapse, just return and let the guest try again. > */ > - if (!ptep) { > - local_irq_enable(); > + if (!pte_present(pte)) { > if (page) > put_page(page); > return RESUME_GUEST; > } > - pte = *ptep; > - local_irq_enable(); > hpa = pte_pfn(pte) << PAGE_SHIFT; > pte_size = PAGE_SIZE; > if (shift) > diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c > index 134fbc1..7bf94ba 100644 > --- a/arch/powerpc/kvm/book3s_64_mmu_radix.c > +++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c > @@ -815,18 +815,19 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu, > */ > local_irq_disable(); > ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift); > + pte = __pte(0); > + if (ptep) > + pte = *ptep; > + local_irq_enable(); > /* > * If the PTE disappeared temporarily due to a THP > * collapse, just return and let the guest try again. > */ > - if (!ptep) { > - local_irq_enable(); > + if (!pte_present(pte)) { > if (page) > put_page(page); > return RESUME_GUEST; > } > - pte = *ptep; > - local_irq_enable(); > > /* If we're logging dirty pages, always map single pages */ > large_enable = !(memslot->flags & KVM_MEM_LOG_DIRTY_PAGES); >
