[PATCH v2 1/2] mm: fix the pfn calculation mistake in __ioremap_check_ram

[Yaohui Wang <yaohuiwang@linux.alibaba.com>]

In arch/x86/mm/ioremap.c:__ioremap_check_ram, the original pfn wrapping
calculation may cause the pfn range to ignore the very start page, if
res->start is not page-aligned, or the very end page, if res->end is not
page aligned.

So start_pfn should wrap down the res->start address, and end_pfn should
wrap up the res->end address. This makes the pfn range completely
contain [res->start, res->end] ram range. This check is more strict and is
more reasonable.

Signed-off-by: Ben Luo <luoben@linux.alibaba.com>
Signed-off-by: Yahui Wang <yaohuiwang@linux.alibaba.com>
---
 arch/x86/mm/ioremap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 9e5ccc56f..79adf0d2d 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -74,8 +74,8 @@ static unsigned int __ioremap_check_ram(struct resource *res)
 	if ((res->flags & IORESOURCE_SYSTEM_RAM) != IORESOURCE_SYSTEM_RAM)
 		return 0;
 
-	start_pfn = (res->start + PAGE_SIZE - 1) >> PAGE_SHIFT;
-	stop_pfn = (res->end + 1) >> PAGE_SHIFT;
+	start_pfn = res->start >> PAGE_SHIFT;
+	stop_pfn = (res->end + PAGE_SIZE) >> PAGE_SHIFT;
 	if (stop_pfn > start_pfn) {
 		for (i = 0; i < (stop_pfn - start_pfn); ++i)
 			if (pfn_valid(start_pfn + i) &&
-- 
2.25.1