Re: [PATCH] ata: ahci: force 32-bit DMA for ASMedia ASM1166

[Niklas Cassel <cassel@kernel.org>]

On Mon, Jun 22, 2026 at 02:02:57PM +0100, David Laight wrote:
> On Mon, 22 Jun 2026 20:31:54 +0900
> Damien Le Moal <dlemoal@kernel.org> wrote:
> 
> > On 6/21/26 19:08, Alvin Lim wrote:
> > > The ASMedia ASM1166 SATA controller (1b21:1166) advertises 64-bit DMA
> > > support (AHCI CAP.S64A), but on systems with the IOMMU enabled - where it
> > > can be handed DMA addresses above 4 GB - it silently corrupts data in
> > > transit. Reads return different, wrong data on each access. SMART is clean,
> > > there are no SATA link resets and no MCE is raised, so the corruption is
> > > invisible until it surfaces as filesystem metadata errors (XFS EUCLEAN)
> > > or, on Ceph, mass scrub errors across multiple independent filesystems at
> > > once - i.e. host-level, not filesystem-level.
> > > 
> > > This is the same failure mode already quirked for other controllers that
> > > falsely claim working 64-bit DMA. See commit 105c42566a55 ("ata: ahci:
> > > force 32-bit DMA for JMicron JMB582/JMB585") and commit 20730e9b2778
> > > ("ahci: add 43-bit DMA address quirk for ASMedia ASM1061 controllers").
> > > The ASM1166 currently maps to plain board_ahci with no DMA limit.  
> > 
> > Have you tried the same quirk, limiting DMA to 43-bits ? It is very likely that
> > this adapter bug is the same as the 1061.
> > 
> 
> It would also be worth checking that you get the read fails with a 44-bit mask.
> 
> I'd guess it also requires that you keep the controller busy for (about) 8TB
> of reads - which is where sequential address allocation would exceed 43-bits.
> But that is just conjecture since I've not looked at the iommu code.

The iommu code will by default try to allocate a 32-bit IOVA by default:
https://github.com/torvalds/linux/blob/v7.1/drivers/iommu/dma-iommu.c#L780-L799

Only once a 32-bit IOVA allocation fails, will it start using 64-bit IOVAs.


It is possible to to set iommu.forcedac=1 to allocate from the full usable
IOVA range immediately:
https://github.com/torvalds/linux/blob/v7.1/Documentation/admin-guide/kernel-parameters.txt#L2619


Kind regards,
Niklas