On Wed, Nov 13, 2013 at 01:14:53PM -0800, H. Peter Anvin wrote:
> On 11/13/2013 01:04 PM, Vivek Goyal wrote:
> > [CC hpa ]
> >
> > And this issue brings me to the question that why do we allow sytem RAM
> > ranges which do not start on page boundary or do not end on page boundary.
> > Can't we truncate the BIOS reported RAM ranges in such a way so that
> > they start and end at PAGE boundary and rest of the kernel will never see
> > unaligned portion of RAM and this will make life so much simpler for
> > other tools.
> >
>
> That is a bit of a headache for doing in the memblock space. We do, in
> fact, truncate partial pages, but later in the game. It is possible we
> should push that sooner in the stack.
Hi Peter,
I noticed we seem to be trimming away partial pages in memblock.
memblock_x86_fill() {
/* throw away partial pages */
memblock_trim_memory(PAGE_SIZE);
}
But not in e820 hence they show up in /proc/iomem.
How about something along the lines as below patch. This fixes my
/proc/vmcore mmap() issue.
Thanks
Vivek
---
arch/x86/kernel/e820.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
Index: linux-2.6/arch/x86/kernel/e820.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/e820.c 2013-11-13 10:46:24.938057251 -0500
+++ linux-2.6/arch/x86/kernel/e820.c 2013-11-13 17:36:17.042681842 -0500
@@ -169,6 +169,33 @@ void __init e820_print_map(char *who)
}
}
+static int e820_trim_memory(struct e820entry *map, unsigned int nr_entries,
+ unsigned int align)
+{
+ int i;
+ struct e820entry *ei;
+ u64 start, end, orig_start, orig_end;
+
+ for (i = 0; i < nr_entries; i++) {
+ ei = &map[i];
+ if (ei->type != E820_RAM)
+ continue;
+ orig_start = ei->addr;
+ orig_end = ei->addr + ei->size;
+
+ start = round_up(orig_start, align);
+ end = round_down(orig_end, align);
+
+ if (start == orig_start && end == orig_end)
+ continue;
+
+ ei->addr = start;
+ ei->size = end - start;
+ }
+
+ return 0;
+}
+
/*
* Sanitize the BIOS e820 map.
*
@@ -267,6 +294,8 @@ int __init sanitize_e820_map(struct e820
int old_nr, new_nr, chg_nr;
int i;
+ e820_trim_memory(biosmap, *pnr_map, PAGE_SIZE);
+
/* if there's only one memory region, don't bother */
if (*pnr_map < 2)
return -1;
