Re: [PATCH v3 1/2] iommu/vt-d: Add helper to flush caches for context change
From: Jacob Pan
Date: Tue Jul 02 2024 - 11:53:41 EST
On Tue, 2 Jul 2024 12:43:41 +0800, Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
wrote:
> On 2024/7/2 12:41, Jacob Pan wrote:
> > On Mon, 1 Jul 2024 19:23:16 +0800, Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > wrote:
> >
> >> + if (flush_domains) {
> >> + /*
> >> + * If the IOMMU is running in scalable mode and there
> >> might
> >> + * be potential PASID translations, the caller should
> >> hold
> >> + * the lock to ensure that context changes and cache
> >> flushes
> >> + * are atomic.
> >> + */
> >> + assert_spin_locked(&iommu->lock);
> >> + for (i = 0; i < info->pasid_table->max_pasid; i++) {
> >> + pte = intel_pasid_get_entry(info->dev, i);
> >> + if (!pte || !pasid_pte_is_present(pte))
> >> + continue;
> > Is it worth going through 1M PASIDs just to skip the PASID cache
> > invalidation? Or just do the flush on all used DIDs unconditionally.
>
> Currently we don't track all domains attached to a device. If such
> optimization is necessary, perhaps we can add it later.
I think it is necessary, because without tracking domain IDs, the code
above would have duplicated invalidations.
For example: a device PASID table has the following entries
PASID DomainID
-------------------------
100 1
200 1
300 2
-------------------------
When a present context entry changes, we need to do:
qi_flush_pasid_cache(iommu, 1, QI_PC_ALL_PASIDS, 0);
qi_flush_pasid_cache(iommu, 2, QI_PC_ALL_PASIDS, 0);
With this code, we do
qi_flush_pasid_cache(iommu, 1, QI_PC_ALL_PASIDS, 0);
qi_flush_pasid_cache(iommu, 1, QI_PC_ALL_PASIDS, 0);//duplicated!
qi_flush_pasid_cache(iommu, 2, QI_PC_ALL_PASIDS, 0);
Thanks,
Jacob