On Tue, Sep 09, 2025 at 08:40:28PM -0700, Nicolin Chen wrote:
- level
The number of table hops from the lowest leaf. Level 0
is always a table of only leaves of the least significant VA bits. TheHmm, I am a bit confused here. I thought "leaf" was meant to be a "leaf" table? But here "a table of only leaves" makes it feel like a "leaf" table entry?
How aboutL:
* level * Level 0 is always a table of only leaves with no futher table pointers. * Increasing levels increase the size of the table items. The least * significant VA bits used to index page tables are used to index the Level * 0 table. The various labels for table levels used by HW descriptions are * not used.
- table
A linear array of entries representing the translation items for that
level.
- index
The position in a table of an element: item = table[index]
- item
A single position in a table
- entry
A single logical element in a table. If contiguous pages are not
supported then item and entry are the same thing, otherwise entry refers
to the all the items that comprise a single contiguous translation.So, an "entry" is a group of "items" if contiguous pages (huge page?) are supported.
Yes
Then, the "entry" sounds like a physical (v.s. "logical") table entry, e.g. a PTE that we usually say?
I choose entry because it is related to PTE and in most cases you want to work on the entries. The replication of entry to item is somewhat hidden.
From a HW perspective the TLB should be loading entries.
+#if !IS_ENABLED(CONFIG_GENERIC_ATOMIC64) +static inline bool pt_table_install64(struct pt_state *pts, u64 table_entry) +{
- u64 *entryp = pt_cur_table(pts, u64) + pts->index;
- u64 old_entry = pts->entry;
- bool ret;
- /*
* Ensure the zero'd table content itself is visible before its PTE can* be. release is a NOP on !SMP, but the HW is still doing an acquire.*/- if (!IS_ENABLED(CONFIG_SMP))
dma_wmb();Mind elaborating why SMP doesn't need this?
The command says the "relase is a NOP" it means this:
ret = try_cmpxchg64_release(entryp, &old_entry, table_entry);
On SMP release does an actual release, on UP it doesn't have a barrier.
Otherwise, these validations wouldn't be effective?
drivers/iommu/generic_pt/pt_iter.h:388: if (PT_WARN_ON(!pts->table_lower)) drivers/iommu/generic_pt/pt_iter.h-389- return -EINVAL;
Right, when PT_WARN_ON is disabled it does nothing and never evaluates its expression. All the branches like the above are removed.
Jason