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Date:   Thu, 06 Aug 2020 23:38:56 -0000
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Subject: [tip: x86/kaslr] x86/kaslr: Simplify process_gb_huge_pages()
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        Ingo Molnar <mingo@kernel.org>, x86 <x86@kernel.org>,
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The following commit has been merged into the x86/kaslr branch of tip:

Commit-ID:     be9e8d9541a95bdfac1c13d112cc032ea7fc745f
Gitweb:        https://git.kernel.org/tip/be9e8d9541a95bdfac1c13d112cc032ea7fc745f
Author:        Arvind Sankar <nivedita@alum.mit.edu>
AuthorDate:    Tue, 28 Jul 2020 18:57:13 -04:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 31 Jul 2020 11:08:17 +02:00

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
---
 arch/x86/boot/compressed/kaslr.c | 47 +++++++++++++------------------
 1 file changed, 21 insertions(+), 26 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 3727e97..00ef84b 100644
--- 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);
 	}
 }