Re: 5.10.40 dom0 kernel - nvme: Invalid SGL for payload:131072 nents:13

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.07.2021 16:19, Andy Smith wrote:
> On Wed, Jul 21, 2021 at 10:10:13AM +0200, Jan Beulich wrote:
>> Since xen-blkback only talks in terms of bio-s, I don't think it is
>> the party responsible for honoring such driver restrictions. Instead
>> I'd expect the block layer's bio merging to be where this needs to be
>> observed. Perhaps it simply doesn't expect to be passed requests in
>> multiples of 11 sectors together with the capping at 64k (as said -
>> iirc) and driver restrictions on where splits may occur? And as to
>> earlier Linux versions working - perhaps the merging logic was less
>> aggressive back then?
> 
> I later realised that there was another change in my setup besides
> the kernel version going from 4.19 to 5.10: I gave the dom0 8GiB of
> memory instead of the 3GiB it had before.
> 
> I understand that below 4GiB memory use of swiotlb is disabled so
> all the time previously this was not used, and now is. Perhaps the
> bug is in there?
> 
> I was told that the only simple way on a Xen dom0 to disable use of
> swiotlb would be to set the memory below 4GiB again, so I might try
> that.

I have no idea where you take this 4GiB aspect from. What the kernel
considers "below 4GiB" in its view of the world may be at a much
higher address in system address space. And the mere amount of
memory doesn't matter here at all.

> I was also pointed to this patch as a maybe fix for my issue:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=5f89468e2f060031cd89fd4287298e0eaf246bf6

Yes, this looks possibly related.

Jan