From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
Sent: Thursday, November 7, 2024 12:21 PM
On 2024/11/7 10:52, Baolu Lu wrote:
On 11/6/24 23:45, Yi Liu wrote:
+int intel_pasid_replace_first_level(struct intel_iommu *iommu,
+ struct device *dev, pgd_t *pgd,
+ u32 pasid, u16 did, u16 old_did,
+ int flags)
+{
+ struct pasid_entry *pte;
+
+ if (!ecap_flts(iommu->ecap)) {
+ pr_err("No first level translation support on %s\n",
+ iommu->name);
+ return -EINVAL;
+ }
+
+ if ((flags & PASID_FLAG_FL5LP) && !cap_fl5lp_support(iommu-
>cap)) {
+ pr_err("No 5-level paging support for first-level on %s\n",
+ iommu->name);
+ return -EINVAL;
+ }
+
+ spin_lock(&iommu->lock);
+ pte = intel_pasid_get_entry(dev, pasid);
+ if (!pte) {
+ spin_unlock(&iommu->lock);
+ return -ENODEV;
+ }
+
+ if (!pasid_pte_is_present(pte)) {
+ spin_unlock(&iommu->lock);
+ return -EINVAL;
+ }
+
+ WARN_ON(old_did != pasid_get_domain_id(pte));
+
+ pasid_pte_config_first_level(iommu, pte, pgd, did, flags);
+ spin_unlock(&iommu->lock);
+
+ intel_pasid_flush_present(iommu, dev, pasid, old_did, pte);
+ intel_iommu_drain_pasid_prq(dev, pasid);
+
+ return 0;
+}
pasid_pte_config_first_level() causes the pasid entry to transition from
present to non-present and then to present. In this case, calling
intel_pasid_flush_present() is not accurate, as it is only intended for
pasid entries transitioning from present to present, according to the
specification.
It's recommended to move pasid_clear_entry(pte) and
pasid_set_present(pte) out to the caller, so ...
For setup case (pasid from non-present to present):
- pasid_clear_entry(pte)
- pasid_pte_config_first_level(pte)
- pasid_set_present(pte)
- cache invalidations
For replace case (pasid from present to present)
- pasid_pte_config_first_level(pte)
- cache invalidations
The same applies to other types of setup and replace.
hmmm. Here is the reason I did it in the way of this patch:
1) pasid_clear_entry() can clear all the fields that are not supposed to
be used by the new domain. For example, converting a nested domain to
SS
only domain, if no pasid_clear_entry() then the FSPTR would be there.
Although spec seems not enforce it, it might be good to clear it.
2) We don't support atomic replace yet, so the whole pasid entry
transition
is not done in one shot, so it looks to be ok to do this stepping
transition.
3) It seems to be even worse if keep the Present bit during the
transition.
The pasid entry might be broken while the Present bit indicates
this is
a valid pasid entry. Say if there is in-flight DMA, the result may be
unpredictable.
Based on the above, I chose the current way. But I admit if we are
going to
support atomic replace, then we should refactor a bit. I believe at that
time we need to construct the new pasid entry first and try to exchange it
to the pasid table. I can see some transition can be done in that way
as we
can do atomic exchange with 128bits. thoughts? 🙂
