arm64: mm: Simplify __flush_tlb_range_limit_excess()

__flush_tlb_range_limit_excess() is unnecessarily complicated:

  - It takes a 'start', 'end' and 'pages' argument, whereas it only
    needs 'pages' (which the caller has computed from the other two
    arguments!).

  - It erroneously compares 'pages' with MAX_TLBI_RANGE_PAGES when
    the system doesn't support range-based invalidation but the range to
    be invalidated would result in fewer than MAX_DVM_OPS invalidations.

Simplify the function so that it no longer takes the 'start' and 'end'
arguments and only considers the MAX_TLBI_RANGE_PAGES threshold on
systems that implement range-based invalidation.

Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: willdeacon

arch/arm64/include/asm/tlbflush.h

@@ -537,21 +537,19 @@ static __always_inline void __flush_tlb_range_op(tlbi_op lop, tlbi_op rop,
 #define __flush_s2_tlb_range_op(op, start, pages, stride, tlb_level) \
 	__flush_tlb_range_op(op, r##op, start, pages, stride, 0, tlb_level, kvm_lpa2_is_enabled())
 
-static inline bool __flush_tlb_range_limit_excess(unsigned long start,
-		unsigned long end, unsigned long pages, unsigned long stride)
+static inline bool __flush_tlb_range_limit_excess(unsigned long pages,
+						  unsigned long stride)
 {
 	/*
-	 * When the system does not support TLB range based flush
-	 * operation, (MAX_DVM_OPS - 1) pages can be handled. But
-	 * with TLB range based operation, MAX_TLBI_RANGE_PAGES
-	 * pages can be handled.
+	 * Assume that the worst case number of DVM ops required to flush a
+	 * given range on a system that supports tlb-range is 20 (4 scales, 1
+	 * final page, 15 for alignment on LPA2 systems), which is much smaller
+	 * than MAX_DVM_OPS.
 	 */
-	if ((!system_supports_tlb_range() &&
-	     (end - start) >= (MAX_DVM_OPS * stride)) ||
-	    pages > MAX_TLBI_RANGE_PAGES)
-		return true;
+	if (system_supports_tlb_range())
+		return pages > MAX_TLBI_RANGE_PAGES;
 
-	return false;
+	return pages >= (MAX_DVM_OPS * stride) >> PAGE_SHIFT;
 }
 
 static inline void __flush_tlb_range_nosync(struct mm_struct *mm,
@@ -565,7 +563,7 @@ static inline void __flush_tlb_range_nosync(struct mm_struct *mm,
 	end = round_up(end, stride);
 	pages = (end - start) >> PAGE_SHIFT;
 
-	if (__flush_tlb_range_limit_excess(start, end, pages, stride)) {
+	if (__flush_tlb_range_limit_excess(pages, stride)) {
 		flush_tlb_mm(mm);
 		return;
 	}
@@ -629,7 +627,7 @@ static inline void flush_tlb_kernel_range(unsigned long start, unsigned long end
 	end = round_up(end, stride);
 	pages = (end - start) >> PAGE_SHIFT;
 
-	if (__flush_tlb_range_limit_excess(start, end, pages, stride)) {
+	if (__flush_tlb_range_limit_excess(pages, stride)) {
 		flush_tlb_all();
 		return;
 	}