Subject: [RFC PATCH 2/3] mm/vmalloc.c: Only flush VM_FLUSH_RESET_PERMS area immediately

From: Baoquan He <[email-masked]>
Date: Fri, 19 May 2023 20:02:10 +0800

When freeing vmalloc range mapping, only unmapping the page tables is
done, TLB flush is lazily deferred to a late stage until
lazy_max_pages() is met or vmalloc() can't find available virtual memory
region.

However, to free VM_FLUSH_RESET_PERMS memory of vmalloc, TLB flushing
need be done immediately before freeing pages, and the direct map
needs resetting permissions and TLB flushing. Please see commit
868b104d7379 ("mm/vmalloc: Add flag for freeing of special permsissions")
for more details.

In the current code, when freeing VM_FLUSH_RESET_PERMS memory, lazy
purge is also done to try to save a TLB flush later. When doing that, it
merges the direct map range with the percpu vbq dirty range and all
purge ranges by calculating flush range of [min:max]. That will add the
huge gap between direct map range and vmalloc range into the final TLB
flush range. So here, only flush VM_FLUSH_RESET_PERMS area immediately,
and leave the lazy flush to the normal points, e.g when allocating
a new vmap_area, or lazy_max_pages() is met.

Signed-off-by: Baoquan He <[email-masked]>
---
 mm/vmalloc.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 31e8d9e93650..87134dd8abc3 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2690,9 +2690,10 @@ static inline void set_area_direct_map(const struct vm_struct *area,
  */
 static void vm_reset_perms(struct vm_struct *area)
 {
-	unsigned long start = ULONG_MAX, end = 0;
+	unsigned long start = ULONG_MAX, end = 0, pages = 0;
 	unsigned int page_order = vm_area_page_order(area);
-	int flush_dmap = 0;
+	struct list_head local_flush_list;
+	struct vmap_area alias_va, va;
 	int i;
 
 	/*
@@ -2708,17 +2709,33 @@ static void vm_reset_perms(struct vm_struct *area)
 			page_size = PAGE_SIZE << page_order;
 			start = min(addr, start);
 			end = max(addr + page_size, end);
-			flush_dmap = 1;
 		}
 	}
 
+	va.va_start = (unsigned long)area->addr;
+	va.va_end = (unsigned long)(area->addr + area->size);
 	/*
 	 * Set direct map to something invalid so that it won't be cached if
 	 * there are any accesses after the TLB flush, then flush the TLB and
 	 * reset the direct map permissions to the default.
 	 */
 	set_area_direct_map(area, set_direct_map_invalid_noflush);
-	_vm_unmap_aliases(start, end, flush_dmap);
+	if (IS_ENABLED(CONFIG_HAVE_FLUSH_TLB_KERNEL_VAS)) {
+		if (end > start) {
+			pages = (end - start) >> PAGE_SHIFT;
+			alias_va.va_start = (unsigned long)start;
+			alias_va.va_end = (unsigned long)end;
+			list_add(&alias_va.list, &local_flush_list);
+		}
+
+		pages += area->size >> PAGE_SHIFT;
+		list_add(&va.list, &local_flush_list);
+
+		flush_tlb_kernel_vas(&local_flush_list, pages);
+	} else {
+		flush_tlb_kernel_range(start, end);
+		flush_tlb_kernel_range(va.va_start, va.va_end);
+	}
 	set_area_direct_map(area, set_direct_map_default_noflush);
 }
 
-- 
2.34.1

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