Re: [PATCH v2 03/12] iommu: Remove unrecoverable fault data

[Jason Gunthorpe]

On Thu, Aug 10, 2023 at 10:27:21AM +0800, Baolu Lu wrote:
> On 2023/8/10 0:59, Jason Gunthorpe wrote:
> > On Thu, Jul 27, 2023 at 01:48:28PM +0800, Lu Baolu wrote:
> > > The unrecoverable fault data is not used anywhere. Remove it to avoid
> > > dead code.
> > > 
> > > Suggested-by: Kevin Tian<kevin.tian@xxxxxxxxx>
> > > Signed-off-by: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > > ---
> > >   include/linux/iommu.h | 70 +------------------------------------------
> > >   1 file changed, 1 insertion(+), 69 deletions(-)
> > Do we plan to bring this back in some form? A driver specific fault
> > report via iommufd?
> 
> I can hardly see the possibility.
> 
> The only necessary dma fault messages are the offending address and the
> permissions. With these, the user space device model software knows that
> "a DMA fault was generated when the IOMMU hardware tried to translate
> the offending address with the given permissions".
> 
> And then, the device model software will walk the page table and figure
> out what is missed before injecting the vendor-specific fault messages
> to the VM guest.

Avoiding walking the page table sounds like a pretty big win if we
could manage it by forwarding more event data..

Jason