arm64: tlbi: Set MAX_TLBI_OPS to PTRS_PER_PTE

In order to reduce the possibility of soft lock-ups, we bound the
maximum number of TLBI operations performed by a single call to
flush_tlb_range() to an arbitrary constant of 1024.

Whilst this does the job of avoiding lock-ups, we can actually be a bit
smarter by defining this as PTRS_PER_PTE. Due to the structure of our
page tables, using PTRS_PER_PTE means that an outer loop calling
flush_tlb_range() for entire table entries will end up performing just a
single TLBI operation for each entry. As an example, mremap()ing a 1GB
range mapped using 4k pages now requires only 512 TLBI operations when
moving the page tables as opposed to 262144 operations (512*512) when
using the current threshold of 1024.

Cc: Joel Fernandes <joel@joelfernandes.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/tlbflush.h

@@ -186,7 +186,7 @@ static inline void flush_tlb_page(struct vm_area_struct *vma,
  * This is meant to avoid soft lock-ups on large TLB flushing ranges and not
  * necessarily a performance improvement.
  */
-#define MAX_TLBI_OPS	1024UL
+#define MAX_TLBI_OPS	PTRS_PER_PTE
 
 static inline void __flush_tlb_range(struct vm_area_struct *vma,
 				     unsigned long start, unsigned long end,
@@ -195,7 +195,7 @@ static inline void __flush_tlb_range(struct vm_area_struct *vma,
 	unsigned long asid = ASID(vma->vm_mm);
 	unsigned long addr;
 
-	if ((end - start) > (MAX_TLBI_OPS * stride)) {
+	if ((end - start) >= (MAX_TLBI_OPS * stride)) {
 		flush_tlb_mm(vma->vm_mm);
 		return;
 	}