On 30/06/2023 02:54, John Hubbard wrote:

On 6/22/23 07:42, Ryan Roberts wrote:

quoted

With the ptep API sufficiently refactored, we can now introduce a new
"contpte" API layer, which transparently manages the PTE_CONT bit for
user mappings. Whenever it detects a set of PTEs that meet the
requirements for a contiguous range, the PTEs are re-painted with the
PTE_CONT bit.

This initial change provides a baseline that can be optimized in future
commits. That said, fold/unfold operations (which imply tlb
invalidation) are avoided where possible with a few tricks for
access/dirty bit management.

Write-enable and write-protect modifications are likely non-optimal and
likely incure a regression in fork() performance. This will be addressed
separately.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---

Hi Ryan!

While trying out the full series from your gitlab features/granule_perf/all
branch, I found it necessary to EXPORT a symbol in order to build this.

Thanks for the bug report!

Please see below:

...

quoted

+
+pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte)
+{
+    /*
+     * Gather access/dirty bits, which may be populated in any of the ptes
+     * of the contig range. We are guarranteed to be holding the PTL, so any
+     * contiguous range cannot be unfolded or otherwise modified under our
+     * feet.
+     */
+
+    pte_t pte;
+    int i;
+
+    ptep = contpte_align_down(ptep);
+
+    for (i = 0; i < CONT_PTES; i++, ptep++) {
+        pte = __ptep_get(ptep);
+
+        /*
+         * Deal with the partial contpte_ptep_get_and_clear_full() case,
+         * where some of the ptes in the range may be cleared but others
+         * are still to do. See contpte_ptep_get_and_clear_full().
+         */
+        if (pte_val(pte) == 0)
+            continue;
+
+        if (pte_dirty(pte))
+            orig_pte = pte_mkdirty(orig_pte);
+
+        if (pte_young(pte))
+            orig_pte = pte_mkyoung(orig_pte);
+    }
+
+    return orig_pte;
+}

Here we need something like this, in order to get it to build in all
possible configurations:

EXPORT_SYMBOL_GPL(contpte_ptep_get);

(and a corresponding "#include linux/export.h" at the top of the file).

Because, the static inline functions invoke this routine, above.

A quick grep through the drivers directory shows:

ptep_get() is used by:
  - drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
  - drivers/misc/sgi-gru/grufault.c
  - drivers/vfio/vfio_iommu_type1.c
  - drivers/xen/privcmd.c

ptep_set_at() is used by:
  - drivers/gpu/drm/i915/i915_mm.c
  - drivers/xen/xlate_mmu.c

None of the other symbols are called, but I guess it is possible that out of
tree modules are calling others.

So on the basis that these symbols were previously pure inline, I propose to
export all the contpte_* symbols using EXPORT_SYMBOL() so that anything that was
previously calling them successfully continue to do so. Will include in v2.

Thanks,
Ryan

thanks,

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