Re: [PATCH 2/4] KVM: arm64: Don't serialize if the access flag isn't set

Ricardo Koller
2022-11-30T01:23:29Z

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.

>
> --
> Thanks,
> Oliver