x86: ioremap ram check fix

Hi Ingo,

bdd3cee2e4b7279457139058615ced6c2b41e7de (x86: ioremap(), extend check to all RAM pages) breaks OLPC's ioremap call. The ioremap that OLPC uses is:

        romsig = ioremap(0xffffffc0, 16);

The commit that breaks it is basically:

- for (pfn = phys_addr >> PAGE_SHIFT; pfn < max_pfn_mapped &&
- (pfn << PAGE_SHIFT) < last_addr; pfn++) {
+ for (pfn = phys_addr >> PAGE_SHIFT;
+ (pfn << PAGE_SHIFT) < last_addr; pfn++) {
+

Previously, the 'pfn < max_pfn_mapped' check would've caused us to not enter the loop. Removing that check means we loop infinitely. The reason for that is because pfn is 0xfffff, and last_addr is 0xffffffcf. The remaining check that is used to exit the loop is not sufficient; when pfn<<PAGE_SHIFT is 0xfffff000, that is less than 0xffffffcf; when we increment pfn and it overflows (pfn == 0x100000), pfn<<PAGE_SHIFT ends up being 0. That, of course, is less than last_addr. In effect, pfn<<PAGE_SHIFT is never lower than last_addr.

The simple fix for this is to limit the last_addr check to the PAGE_MASK; a patch is below.

Signed-off-by Andres Salomon <[email protected]>

---

  arch/x86/mm/ioremap.c |    3 ++-
  1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 804de18..fb960f5 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -149,7 +149,8 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,

         * Don't allow anybody to remap normal RAM that we're using..
         */
        for (pfn = phys_addr >> PAGE_SHIFT;
 -                               (pfn << PAGE_SHIFT) < last_addr; pfn++) {
 +                               (pfn << PAGE_SHIFT) < (last_addr & PAGE_MASK);
 +                               pfn++) {

                int is_ram = page_is_ram(pfn);

Hi Ingo,

bdd3cee2e4b7279457139058615ced6c2b41e7de (x86: ioremap(), extend check to all RAM pages) breaks OLPC's ioremap call. The ioremap that OLPC uses is:

Quoted 2 lines · Andres Salomon

Hi Ingo,

Quoted 3 lines

bdd3cee2e4b7279457139058615ced6c2b41e7de (x86: ioremap(), extend check to all RAM pages) breaks OLPC's ioremap call. The ioremap that OLPC uses is:

that breakage has been reported independently as well and the revert has been pushed to Linus yesterday - it's not upstream yet. See this commit in x86.git:

commit 1b8104a0ec138de829bb351f6597d534c7c134dc
Author: Ingo Molnar <[email protected]>
Date: Tue Apr 29 12:04:51 2008 +0200

revert: "x86: ioremap(), extend check to all RAM pages"

Vegard Nossum reported a large (150 seconds) boot delay during bootup, and bisected it to "x86: ioremap(), extend check to all RAM pages" (commit bdd3cee2e4b). Revert this commit for now.

Bisected-by Vegard Nossum <[email protected]>

Signed-off-by Ingo Molnar <[email protected]>

Ingo

Quoted 3 lines

that breakage has been reported independently as well and the revert has been pushed to Linus yesterday - it's not upstream yet. See this commit in x86.git:

Sure, either way. FWIW, Vegard reported that the PAGE_MASK change made the 150s delay disappear.