x86/kaslr: Simplify process_gb_huge_pages()

Replace the loop to determine the number of 1Gb pages with arithmetic.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200728225722.67457-13-nivedita@alum.mit.edu

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 3727e97..00ef84b 100644 (file)
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -547,49 +547,44 @@ static void store_slot_info(struct mem_vector *region, unsigned long image_size)
 static void
 process_gb_huge_pages(struct mem_vector *region, unsigned long image_size)
 {
-       unsigned long addr, size = 0;
+       unsigned long pud_start, pud_end, gb_huge_pages;
        struct mem_vector tmp;
-       int i = 0;
 
        if (!IS_ENABLED(CONFIG_X86_64) || !max_gb_huge_pages) {
                store_slot_info(region, image_size);
                return;
        }
 
-       addr = ALIGN(region->start, PUD_SIZE);
-       /* Did we raise the address above the passed in memory entry? */
-       if (addr < region->start + region->size)
-               size = region->size - (addr - region->start);
-
-       /* Check how many 1GB huge pages can be filtered out: */
-       while (size >= PUD_SIZE && max_gb_huge_pages) {
-               size -= PUD_SIZE;
-               max_gb_huge_pages--;
-               i++;
-       }
+       /* Are there any 1GB pages in the region? */
+       pud_start = ALIGN(region->start, PUD_SIZE);
+       pud_end = ALIGN_DOWN(region->start + region->size, PUD_SIZE);
 
        /* No good 1GB huge pages found: */
-       if (!i) {
+       if (pud_start >= pud_end) {
                store_slot_info(region, image_size);
                return;
        }
 
-       /*
-        * Skip those 'i'*1GB good huge pages, and continue checking and
-        * processing the remaining head or tail part of the passed region
-        * if available.
-        */
-
-       if (addr >= region->start + image_size) {
+       /* Check if the head part of the region is usable. */
+       if (pud_start >= region->start + image_size) {
                tmp.start = region->start;
-               tmp.size = addr - region->start;
+               tmp.size = pud_start - region->start;
                store_slot_info(&tmp, image_size);
        }
 
-       size  = region->size - (addr - region->start) - i * PUD_SIZE;
-       if (size >= image_size) {
-               tmp.start = addr + i * PUD_SIZE;
-               tmp.size = size;
+       /* Skip the good 1GB pages. */
+       gb_huge_pages = (pud_end - pud_start) >> PUD_SHIFT;
+       if (gb_huge_pages > max_gb_huge_pages) {
+               pud_end = pud_start + (max_gb_huge_pages << PUD_SHIFT);
+               max_gb_huge_pages = 0;
+       } else {
+               max_gb_huge_pages -= gb_huge_pages;
+       }
+
+       /* Check if the tail part of the region is usable. */
+       if (region->start + region->size >= pud_end + image_size) {
+               tmp.start = pud_end;
+               tmp.size = region->start + region->size - pud_end;
                store_slot_info(&tmp, image_size);
        }
 }