[dm-devel] AMD-Vi IO_PAGE_FAULTs and ata3.00: failed command: READ FPDMA QUEUED errors since Linux 4.0

[Mikulas Patocka]

On Tue, 29 Sep 2015, Joerg Roedel wrote:

> On Sun, Sep 20, 2015 at 08:50:40AM +0200, Andreas Hartmann wrote:
> > > I would submit this bug to maintainers of AMD-Vi. They understand the 
> > > hardware, so they should tell why do large I/O requests result in 
> > > IO_PAGE_FAULTs.
> > > 
> > > It is probably bug either in AMD-Vi driver or in hardware.
> > 
> > Until now, I didn't hear anything from the maintainers of AMD-Vi.
> 
> What do you mean by this? I've been commenting on this issue in the
> past and I thought we agreed that this is no issue of the IOMMU driver.
> 
> It it were, bisection should lead to a commit that breaks it, but there
> are no commits between v3.18 and v3.19 in the AMD IOMMU driver touching
> the DMA-API path.
> 
> 	Joerg

I don't know why are you so certain that the bug in not in AMD-Vi IOMMU.

There was a patch (34b48db66e08ca1c1bc07cf305d672ac940268dc) that 
increased default block request size. That patch triggers AMD-Vi page 
faults. The bug may be in ATA driver, in ATA controller on in AMD-Vi 
driver or hardware. I didn't see anything in that thread that proves that 
the bug in not in AMD-Vi IOMMU.

The bug probably existed even before kernel 3.19, but it was masked by the 
fact that I/O request size was artifically capped. Bisecting probably 
won't find it, as it may have existed since ever.

Mikulas