> From: Nicolin Chen <nicolinc@xxxxxxxxxx> > 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.
