On Tue, Apr 26, 2022, Mingwei Zhang wrote: > On Tue, Apr 26, 2022 at 6:16 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > > > On Tue, Apr 26, 2022, Mingwei Zhang wrote: > > > > I completely agree that lookup_address() and friends are unnecessarily fragile, > > > > but I think that attempting to harden them to fix this KVM bug will open a can > > > > of worms and end up delaying getting KVM fixed. > > > > > > So basically, we need to: > > > - choose perf_get_page_size() instead of using any of the > > > lookup_address*() in mm. > > > - add a wrapper layer to adapt: 1) irq disabling/enabling and 2) size > > > -> level translation. > > > > > > Agree? > > > > Drat, I didn't see that it returns the page size, not the level. That's a bit > > unfortunate. It definitely makes me less averse to fixing lookup_address_in_pgd() > > > > Hrm. I guess since we know there's at least one broken user, and in theory > > fixing lookup_address_in_pgd() should do no harm to users that don't need protection, > > it makes sense to just fix lookup_address_in_pgd() and see if the x86 maintainers > > push back. > > Yeah, fixing lookup_address_in_pgd() should be cleaner(), since the > page fault usage case does not need irq save/restore. But the other > one needs it. So, we can easily fix the function with READ_ONCE and > lockless staff. But wrapping the function with irq save/restore from > the KVM side. I think it makes sense to do the save/restore in lookup_address_in_pgd(). The Those helpers are exported, so odds are good there are broken users that will benefit from fixing all paths.
