Re: [Qemu-devel] [PATCH 26/26] tcg: Use tlb_fill probe from tlb_vaddr_to_host

[Peter Maydell]

On Thu, 9 May 2019 at 06:24, Richard Henderson
<address@hidden> wrote:
>
> On 4/29/19 10:41 AM, Peter Maydell wrote:
> > On Wed, 3 Apr 2019 at 05:05, Richard Henderson
> > <address@hidden> wrote:
> >>
> >> Most of the existing users would continue around a loop which
> >> would fault the tlb entry in via a normal load/store.  But for
> >> SVE we have a true non-faulting case which requires the new
> >> probing form of tlb_fill.
> >
> > So am I right in thinking that this fixes a bug where we
> > previously would mark a load as faulted if the memory happened
> > not to be in the TLB, whereas now we will correctly pull in the
> > TLB entry and do the load ?
>
> Yes.
>
> > (Since guest code ought to be handling the "non-first-load
> > faulted" case by looping round or otherwise arranging to
> > retry, nothing in practice would have noticed this bug, right?)
>
> Yes.
>
> The only case with changed behaviour is (expected to be) SVE no-fault, where
> the loop you mention would have produced different incorrect results.

OK. If we're fixing a guest-visible bug it would be nice to
describe that in the commit message.

thanks
-- PMM