Re: [PATCH v5 7/8] execmem: add support for cache of large ROX pages

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Op 09-10-2024 om 20:08 schreef Mike Rapoport:
From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>

Using large pages to map text areas reduces iTLB pressure and improves
performance.

Extend execmem_alloc() with an ability to use huge pages with ROX
permissions as a cache for smaller allocations.

To populate the cache, a writable large page is allocated from vmalloc with
VM_ALLOW_HUGE_VMAP, filled with invalid instructions and then remapped as
ROX.

Portions of that large page are handed out to execmem_alloc() callers
without any changes to the permissions.

When the memory is freed with execmem_free() it is invalidated again so
that it won't contain stale instructions.

The cache is enabled when an architecture sets EXECMEM_ROX_CACHE flag in
definition of an execmem_range.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
  include/linux/execmem.h |   2 +
  mm/execmem.c            | 317 +++++++++++++++++++++++++++++++++++++++-
  mm/internal.h           |   1 +
  mm/vmalloc.c            |   5 +
  4 files changed, 320 insertions(+), 5 deletions(-)
[...]
+static void execmem_cache_clean(struct work_struct *work)
+{
+	struct maple_tree *free_areas = &execmem_cache.free_areas;
+	struct mutex *mutex = &execmem_cache.mutex;
+	MA_STATE(mas, free_areas, 0, ULONG_MAX);
+	void *area;
+
+	mutex_lock(mutex);
+	mas_for_each(&mas, area, ULONG_MAX) {
+		size_t size;
+
No need to check for !area, because it is already guaranteed by the while loop condition (mas_for_each)
+		if (!area)
+			continue;
+
+		size = mas_range_len(&mas);
+
+		if (IS_ALIGNED(size, PMD_SIZE) &&
+		    IS_ALIGNED(mas.index, PMD_SIZE)) {
+			struct vm_struct *vm = find_vm_area(area);
+
+			execmem_set_direct_map_valid(vm, true);
+			mas_store_gfp(&mas, NULL, GFP_KERNEL);
+			vfree(area);
+		}
+	}
+	mutex_unlock(mutex);
+}





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