Re: [PATCH] hw/arm/smmuv3: Fix addr_mask for range-based invalidation

[Zenghui Yu]

Hi Eric,

On 2021/1/29 5:30, Auger Eric wrote:
> Hi Zenghui,
>
> On 1/28/21 9:25 AM, Auger Eric wrote:
> > Hi Zenghui,
> >
> > On 12/25/20 10:50 AM, Zenghui Yu wrote:
> > > When performing range-based IOTLB invalidation, we should decode the TG
> > > field into the corresponding translation granule size so that we can pass
> > > the correct invalidation range to backend. Set @granule to (tg * 2 + 10) to
> > > properly emulate the architecture.
> > >
> > > Fixes: d52915616c05 ("hw/arm/smmuv3: Get prepared for range invalidation")
> > > Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
> >
> > Good catch! I tested with older guest kernels though. I wonder how I did
> > not face the bug?
> Please ignore this wrong comment as this corresponds to recent kernels
> instead. Still puzzled anyway ;-)

I noticed this when looking through your nested SMMU series and I didn't
have much clue about the impact on the real setups.

I guess we may receive some unexpected fault events with this bug. But I
think we may miss it for some reasons:

 - the stale TLB entries happen to be evicted due to heavy traffic
 - some form of over-invalidation is performed by your implementation
 - ...

> > > ---
> > >   hw/arm/smmuv3.c | 4 +++-
> > >   1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
> > > index bbca0e9f20..65231c7d52 100644
> > > --- a/hw/arm/smmuv3.c
> > > +++ b/hw/arm/smmuv3.c
> > > @@ -801,7 +801,7 @@ static void smmuv3_notify_iova(IOMMUMemoryRegion *mr,
> > >   {
> > >       SMMUDevice *sdev = container_of(mr, SMMUDevice, iommu);
> > >       IOMMUTLBEvent event;
> > > -    uint8_t granule = tg;
> > > +    uint8_t granule;
> > >   
> > >       if (!tg) {
> > >           SMMUEventInfo event = {.inval_ste_allowed = true};
> > > @@ -821,6 +821,8 @@ static void smmuv3_notify_iova(IOMMUMemoryRegion *mr,
> > >               return;
> > >           }
> > >           granule = tt->granule_sz;
> > > +    } else {
> > > +        guanule = tg * 2 + 10;
> > maybe just init granule to this value above while fixing the typo.

My intention is to initialize @granule to this value explicitly for the
range-based invalidation case. But I'm okay with either way.


Thanks,
Zenghui