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

[Richard Henderson]

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.


r~