On Mon, Mar 13, 2023, David Matlack wrote:
> On Mon, Mar 13, 2023 at 8:53 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> >
> > +David
> >
> > On Mon, Mar 13, 2023, Marc Zyngier wrote:
> > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > > index 7113587222ff..d7b8b25942df 100644
> > > --- a/arch/arm64/kvm/mmu.c
> > > +++ b/arch/arm64/kvm/mmu.c
> > > @@ -666,14 +666,23 @@ static int get_user_mapping_size(struct kvm *kvm, u64 addr)
> > > CONFIG_PGTABLE_LEVELS),
> > > .mm_ops = &kvm_user_mm_ops,
> > > };
> > > + unsigned long flags;
> > > kvm_pte_t pte = 0; /* Keep GCC quiet... */
> > > u32 level = ~0;
> > > int ret;
> > >
> > > + /*
> > > + * Disable IRQs so that we hazard against a concurrent
> > > + * teardown of the userspace page tables (which relies on
> > > + * IPI-ing threads).
> > > + */
> > > + local_irq_save(flags);
> > > ret = kvm_pgtable_get_leaf(&pgt, addr, &pte, &level);
> > > - VM_BUG_ON(ret);
> > > - VM_BUG_ON(level >= KVM_PGTABLE_MAX_LEVELS);
> > > - VM_BUG_ON(!(pte & PTE_VALID));
> > > + local_irq_restore(flags);
> > > +
> > > + /* Oops, the userspace PTs are gone... */
> > > + if (ret || level >= KVM_PGTABLE_MAX_LEVELS || !(pte & PTE_VALID))
> > > + return -EFAULT;
> >
> > I don't think this should return -EFAULT all the way out to userspace. Unless
> > arm64 differs from x86 in terms of how the userspace page tables are managed, not
> > having a valid translation _right now_ doesn't mean that one can't be created in
> > the future, e.g. by way of a subsequent hva_to_pfn().
> >
> > FWIW, the approach x86 takes is to install a 4KiB (smallest granuale) translation,
>
> If I'm reading the ARM code correctly, returning -EFAULT here will
> have that effect. get_user_mapping_size() is only called by
> transparent_hugepage_adjust() which returns PAGE_SIZE if
> get_user_mapping_size() returns anything less than PMD_SIZE.
No, this patch adds
+ int sz = get_user_mapping_size(kvm, hva);
+
+ if (sz < 0)
+ return sz;
+
+ if (sz < PMD_SIZE)
+ return PAGE_SIZE;
+
and
vma_pagesize = transparent_hugepage_adjust(kvm, memslot,
hva, &pfn,
&fault_ipa);
+
+ if (vma_pagesize < 0) {
+ ret = vma_pagesize;
+ goto out_unlock;
+ }
