Re: [RFC PATCH v10 5/5] iommu/vt-d: don't loop for timeout ATS Invalidation request forever

[Baolu Lu]

On 1/10/24 4:40 PM, Ethan Zhao wrote:
> On 1/10/2024 1:28 PM, Baolu Lu wrote:
> > On 12/29/23 1:05 AM, Ethan Zhao wrote:
> > > When the ATS Invalidation request timeout happens, the qi_submit_sync()
> > > will restart and loop for the invalidation request forever till it is
> > > done, it will block another Invalidation thread such as the fq_timer
> > > to issue invalidation request, cause the system lockup as following
> > >
> > > [exception RIP: native_queued_spin_lock_slowpath+92]
> > >
> > > RIP: ffffffffa9d1025c RSP: ffffb202f268cdc8 RFLAGS: 00000002
> > >
> > > RAX: 0000000000000101 RBX: ffffffffab36c2a0 RCX: 0000000000000000
> > >
> > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffab36c2a0
> > >
> > > RBP: ffffffffab36c2a0 R8: 0000000000000001 R9: 0000000000000000
> > >
> > > R10: 0000000000000010 R11: 0000000000000018 R12: 0000000000000000
> > >
> > > R13: 0000000000000004 R14: ffff9e10d71b1c88 R15: ffff9e10d71b1980
> > >
> > > ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
> > >
> > > (the left part of exception see the hotplug case of ATS capable device)
> > >
> > > If one endpoint device just no response to the ATS Invalidation request,
> > > but is not gone, it will bring down the whole system, to avoid such
> > > case, don't try the timeout ATS Invalidation request forever.
> > >
> > > Signed-off-by: Ethan Zhao <haifeng.zhao@xxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/iommu/intel/dmar.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
> > > index 0a8d628a42ee..9edb4b44afca 100644
> > > --- a/drivers/iommu/intel/dmar.c
> > > +++ b/drivers/iommu/intel/dmar.c
> > > @@ -1453,7 +1453,7 @@ int qi_submit_sync(struct intel_iommu *iommu, 
> > > struct qi_desc *desc,
> > >       reclaim_free_desc(qi);
> > >       raw_spin_unlock_irqrestore(&qi->q_lock, flags);
> > >   -    if (rc == -EAGAIN)
> > > +    if (rc == -EAGAIN && type !=QI_DIOTLB_TYPE && type != 
> > > QI_DEIOTLB_TYPE)
> > >           goto restart;
> > >         if (iotlb_start_ktime)
> >
> > Above is also unnecessary if qi_check_fault() returns -ETIMEDOUT,
> > instead of -EAGAIN. Or did I miss anything?
>
> It is pro if we fold it into qi_check_fault(), the con is we have to add
>
> more parameter to qi_check_fault(), no need check invalidation type
>
> of QI_DIOTLB_TYPE&QI_DEIOTLB_TYPE in qi_check_fault() ?

No need to check the request type as multiple requests might be batched
together in a single call. This is also the reason why I asked you to
add a flag bit to this helper and make the intention explicit, say,

"This includes requests to interact with a PCI endpoint. The device may
 become unavailable at any time, so do not attempt to retry if ITE is
 detected and the device has gone away."

Best regards,
baolu