From: Nicolin Chen nicolinc@nvidia.com Sent: Friday, July 28, 2023 3:04 AM
On Thu, Jul 27, 2023 at 09:03:01AM -0300, Jason Gunthorpe wrote:
On Wed, Jul 26, 2023 at 07:59:11PM -0700, Nicolin Chen wrote:
I just realized that either my v8 or your version calls unmap() first at the entire cur_ioas. So, there seems to be no point in doing that fallback re-add routine since the cur_ioas isn't the same, which I don't feel quite right...
The point is to restore the access back to how it should be on failure so future use of the accesss still does the right thing.
We already have built into this a certain non-atomicity for mdevs, they can see a pin failure during replace if they race an access during this unmap window. This is similar to the real HW iommu's without atomic replace.
I was concerned about, after the replace, mdev losing all the mappings due to the unmap() call, which means the fallback is not really a status quo. Do you mean that they could pin those lost mappings back?
None of mdev drivers does that.
but we need think about the actual usage. I don't think the user can request ioas change w/o actually reconfiguring the mdev device. Presumably the latter could lead to reconstructure of pinned pages.
so in code-level as Jason said we just need ensure the access is back to an usable state.