Hi Jahan,
On 07/07/2025 12:24, Jahan Murudi wrote:
On 30/06/2025 13:44, Julien Grall wrote:
On 25/06/2025 16:53, Julien Grall wrote:
Hi Jahan,
+ dsb(sy);
Any clue why Linux (mainline) does not do that?
I understand for the PCI passthrough, Xen will be using stage-2, so in theory
the stage-1 could be used by the guest OS. But ultimately, this is the same PCI
device behind. So if it is not coherent, it should be for both stages. Do you
have any pointer to the documentation that would state otherwise?
You're right - coherency characteristics are identical for both stages. My
earlier understanding was incorrect.
Note, I just noticed that IOMMU_FEAT_COHERENT_WALK is not set for the IPMMU. So the
"dsb sy" is coherent. However, I find doubful an IOMMU would have a difference
of coherency between two stages. So maybe we should set the flag either unconditionally
or based on a register.
Excellent observation. Current R-car IPMMU doesn't supports coherent walks - we
should indeed set this flag unconditionally.
To clarify, the R-car IPMMU doesn't support coherent walk, then the flag
IOMMU_FEAT_COHERENT_WALK *must not* be set.
Cheers,
--
Julien Grall
