On 14.05.2025 13:40, Roger Pau Monné wrote: > On Wed, May 03, 2023 at 11:46:11AM +0200, Jan Beulich wrote: >> We don't need to invalidate caches here; all we're after is that earlier >> writes have made it to main memory (and aiui even that just in case). >> >> Signed-off-by: Jan Beulich <jbeul...@suse.com> >> --- >> This, aiui, being an analogue to uses of iommu_sync_cache() (just not >> range restricted), I wonder whether it shouldn't be conditional upon >> iommu_non_coherent. Then again I'm vaguely under the impression that >> we had been here before, possibly even as far as questioning the need >> for this call altogether. > > I think yes, it would better be only done for iommu_non_coherent. Yet > in that case I wonder why we need this wide flush. In principle all > accesses should already have their own write-back calls if the IOMMU > is non-coherent? > > There's maybe the call from vtd_crash_shutdown() which I guess could > trigger in the middle of some interaction with the IOMMU, but at that > point do we really care to flush anyway if Xen is going to crash? > > Otherwise it seems fine to switch to write-back.
In which case why don't we do it in two steps: This patch, and then one removing the call altogether. Just in case the latter one turns out wrong for whatever reason. Jan
