On Wed, 30 Nov 2022 01:23:20 +0000, Ricardo Koller <ricarkol@xxxxxxxxxx> wrote: > > On Tue, Nov 29, 2022 at 09:15:21PM +0000, Oliver Upton wrote: > > Hi Ricardo, > > > > Thanks for having a look. > > > > On Tue, Nov 29, 2022 at 12:52:12PM -0800, Ricardo Koller wrote: > > > On Tue, Nov 29, 2022 at 07:19:44PM +0000, Oliver Upton wrote: > > > > [...] > > > > > > + ret = stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0, > > > > + &pte, NULL, 0); > > > > + if (!ret) > > > > + dsb(ishst); > > > > > > At the moment, the only reason for stage2_update_leaf_attrs() to not > > > update the PTE is if it's not valid: > > > > > > if (!kvm_pte_valid(pte)) > > > return 0; > > > > > > I guess you could check that as well: > > > > > > + if (!ret || kvm_pte_valid(pte)) > > > + dsb(ishst); > > > > Thanks for catching this. > > > > Instead of pivoting on the returned PTE value, how about we return > > -EAGAIN from the early return in stage2_attr_walker()? It would better > > match the pattern used elsewhere in the pgtable code. > > That works, although I would use another return code (e.g., EINVAL)? as > that's not exactly a "try again" type of error. EINVAL usually is an indication of something that went horribly wrong. But is that really a failure mode? Here, failing to update the PTE should not be considered a failure, but just a benign race: access fault being taken on a CPU and the page being evicted on another (not unlikely, as the page was marked old before). And if I'm correct above, this is definitely a "try again" situation: you probably won't take the same type of fault the second time though. Thanks, M. -- Without deviation from the norm, progress is not possible.
