Re: BUG kernel 6.12.19 defautl_swiotlb_limit() returns wrong value for CONFIG_SWIOTLB_DYNAMIC=y effects atm only under XEN dom0

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 18.09.2026 08:37, James Dingwall wrote:
> I've been having a problem with a Dell HBA330 SCSI controller (mpt3sas)
> when booting under Xen and CONFIG_SWIOTLB_DYNAMIC=y is set.  I had a
> similar issue with a megaraid_sas card that I previously posted about:
>
> https://lkml.iu.edu/hypermail/linux/kernel/2407.3/08254.html
>
> In that case we rebuilt the kernel with CONFIG_SWIOTLB_DYNAMIC=n.
> While investigating the current problem I came across a patch that was
> posted on the xen-devel list:
>
> https://protect2.fireeye.com/v1/url?k=202f9c3b-7fb4525f-202e1774-000babda0201-d2724d878716e4ba&q=1&e=538195f2-f8bd-499e-8576-5e3d7c8ebca6&u=https%3A%2F%2Flists.xen.org%2Farchives%2Fhtml%2Fxen-devel%2F2025-05%2Fmsg00991.html
>
> I have applied that to the Ubuntu 7.0.0-31 kernel sources which has
> resolved the controller initialisation error I was encountering and the
> system now boots as expected.
>
> [    3.921136] mpt3sas_cm0: no suitable DMA mask for 0000:03:00.0
> [    3.921275] mpt3sas_cm0: failure at drivers/scsi/mpt3sas/mpt3sas_scsih.c:13610/_scsih_probe()!
>
> I've included the patch below, I don't have the author's real address
> for the s-o-b.  I'm able to test alternative fixes if there are any
> issues with this one.


https://lore.kernel.org/xen-devel/93625976-e8af-4c39-90fb-45c926d420fd@a-greve.de/


Andreas: could You send Your fix with a bit more elaborated description and to the
proper recipients (hint: use scripts/get_maintainer.pl tool), so it can be reviewed
and potentially applied?

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland