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x86, mm: Fix page table early allocation offset checking 

During debugging loading kernel above 4G, found that one page is not used
in pre-allocated BRK area for early page allocation.
pgt_buf_top is address that can not be used, so should check if that new
end is above that top, otherwise last page will not be used.

Fix that checking and also add print out for allocation from pre-allocated
BRK area to catch possible bugs later.

But after we get back that page for pgt, it tiggers one bug in pgt allocation
with xen: We need to avoid to use page as pgt to map range that is
overlapping with that pgt page.

Add checking about overlapping, when it happens, use memblock allocation
instead.  That fixes crash on Xen PV guest with 2G that Stefan found.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1359058816-7615-2-git-send-email-yinghai@kernel.org
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Tested-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Yinghai Lu 2013-01-24 12:19:42 -08:00 committed by H. Peter Anvin
parent de65d816aa
commit c9b3234a6a
1 changed files with 12 additions and 1 deletions
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13
arch/x86/mm/init.c
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@ -25,6 +25,8 @@ static unsigned long __initdata pgt_buf_top;
static unsigned long min_pfn_mapped;
static bool __initdata can_use_brk_pgt = true;
/*
* Pages returned are already directly mapped.
*
@ -47,7 +49,7 @@ __ref void *alloc_low_pages(unsigned int num)
__GFP_ZERO, order);
}
if ((pgt_buf_end + num) >= pgt_buf_top) {
if ((pgt_buf_end + num) > pgt_buf_top || !can_use_brk_pgt) {
unsigned long ret;
if (min_pfn_mapped >= max_pfn_mapped)
panic("alloc_low_page: ran out of memory");
@ -61,6 +63,8 @@ __ref void *alloc_low_pages(unsigned int num)
} else {
pfn = pgt_buf_end;
pgt_buf_end += num;
printk(KERN_DEBUG "BRK [%#010lx, %#010lx] PGTABLE\n",
pfn << PAGE_SHIFT, (pgt_buf_end << PAGE_SHIFT) - 1);
}
for (i = 0; i < num; i++) {
@ -370,8 +374,15 @@ static unsigned long __init init_range_memory_mapping(
if (start >= end)
continue;
/*
* if it is overlapping with brk pgt, we need to
* alloc pgt buf from memblock instead.
*/
can_use_brk_pgt = max(start, (u64)pgt_buf_end<<PAGE_SHIFT) >=
min(end, (u64)pgt_buf_top<<PAGE_SHIFT);
init_memory_mapping(start, end);
mapped_ram_size += end - start;
can_use_brk_pgt = true;
}
return mapped_ram_size;