* kexec-tools and multiboot breakage
@ 2014-01-15 3:25 Peter Chubb
2014-01-15 3:48 ` Simon Horman
0 siblings, 1 reply; 4+ messages in thread
From: Peter Chubb @ 2014-01-15 3:25 UTC (permalink / raw)
To: horms; +Cc: kexec
Hi Simon,
When you get a moment, please check out
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=735360
Quick summary:
If your kernel is configured to protect the first few pages of
physical memory, then low memory doesn't start at location 0 --- so
when scanning the memory ranges from /proc/iomem, the code in
kexec/arch/i386/kexec-multiboot-x86.c never fills in mem_lower.
I think it's safe to assume that if a memory segment starts at 64k or
lower, it can be extended to location 0 because of the kernel
protection on a PC99-style architecture.
Peter C
--
Dr Peter Chubb peter.chubb AT nicta.com.au
http://www.ssrg.nicta.com.au Software Systems Research Group/NICTA
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: kexec-tools and multiboot breakage
2014-01-15 3:25 kexec-tools and multiboot breakage Peter Chubb
@ 2014-01-15 3:48 ` Simon Horman
2014-01-15 21:39 ` [PATCH] Fix value of mbi->mem_lower for multiboot-x86 Peter Chubb
0 siblings, 1 reply; 4+ messages in thread
From: Simon Horman @ 2014-01-15 3:48 UTC (permalink / raw)
To: Peter Chubb; +Cc: kexec
On Wed, Jan 15, 2014 at 01:25:49PM +1000, Peter Chubb wrote:
> Hi Simon,
> When you get a moment, please check out
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=735360
>
> Quick summary:
> If your kernel is configured to protect the first few pages of
> physical memory, then low memory doesn't start at location 0 --- so
> when scanning the memory ranges from /proc/iomem, the code in
> kexec/arch/i386/kexec-multiboot-x86.c never fills in mem_lower.
>
> I think it's safe to assume that if a memory segment starts at 64k or
> lower, it can be extended to location 0 because of the kernel
> protection on a PC99-style architecture.
Hi Peter,
that approach seems reasonable to me. Could you formally post
the patch to the kexec list with me CCed? I would like a Signed-off-by
line. Thanks.
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^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH] Fix value of mbi->mem_lower for multiboot-x86
2014-01-15 3:48 ` Simon Horman
@ 2014-01-15 21:39 ` Peter Chubb
2014-01-16 0:22 ` Simon Horman
0 siblings, 1 reply; 4+ messages in thread
From: Peter Chubb @ 2014-01-15 21:39 UTC (permalink / raw)
To: kexec; +Cc: Simon Horman, Peter Chubb
In the multiboot header, there is a field, `mem_lower' that is meant to
contain the size of memory starting at zero and ending below 640k.
If your kernel is compiled with CONFIG_X86_RESERVE_LOW non zero
(the usual case), then a hole is inserted into kernel's physical
memory map at zero, so the test to find the size of this region in
kexec/arch/i386/kexec-multiboot-x86.c never succeeds, so the value is
always zero.
On a PC99 architecture, there is always memory at physycal address zero;
assume that a region that starts below 64k actually starts at zero,
and use it for the mem_lower variable.
Signed-off-by: Peter Chubb <peter.chubb@nicta.com.au>
---
kexec/arch/i386/kexec-multiboot-x86.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
Index: kexec-tools-2.0.4/kexec/arch/i386/kexec-multiboot-x86.c
===================================================================
--- kexec-tools-2.0.4.orig/kexec/arch/i386/kexec-multiboot-x86.c 2013-03-14 18:45:16.000000000 +1000
+++ kexec-tools-2.0.4/kexec/arch/i386/kexec-multiboot-x86.c 2014-01-15 10:21:02.138172304 +1000
@@ -261,10 +261,18 @@ int multiboot_x86_load(int argc, char **
mmap[i].length_high = length >> 32;
if (range[i].type == RANGE_RAM) {
mmap[i].Type = 1; /* RAM */
- /* Is this the "low" memory? */
- if ((range[i].start == 0)
- && (range[i].end > mem_lower))
+ /*
+ * Is this the "low" memory? Can't just test
+ * against zero, because Linux protects (and
+ * hides) the first few pages of physical
+ * memory.
+ */
+
+ if ((range[i].start <= 64*1024)
+ && (range[i].end > mem_lower)) {
+ range[i].start = 0;
mem_lower = range[i].end;
+ }
/* Is this the "high" memory? */
if ((range[i].start <= 0x100000)
&& (range[i].end > mem_upper + 0x100000))
--
Dr Peter Chubb peter.chubb AT nicta.com.au
http://www.ssrg.nicta.com.au Software Systems Research Group/NICTA
_______________________________________________
kexec mailing list
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix value of mbi->mem_lower for multiboot-x86
2014-01-15 21:39 ` [PATCH] Fix value of mbi->mem_lower for multiboot-x86 Peter Chubb
@ 2014-01-16 0:22 ` Simon Horman
0 siblings, 0 replies; 4+ messages in thread
From: Simon Horman @ 2014-01-16 0:22 UTC (permalink / raw)
To: Peter Chubb; +Cc: kexec
On Thu, Jan 16, 2014 at 08:39:06AM +1100, Peter Chubb wrote:
>
> In the multiboot header, there is a field, `mem_lower' that is meant to
> contain the size of memory starting at zero and ending below 640k.
> If your kernel is compiled with CONFIG_X86_RESERVE_LOW non zero
> (the usual case), then a hole is inserted into kernel's physical
> memory map at zero, so the test to find the size of this region in
> kexec/arch/i386/kexec-multiboot-x86.c never succeeds, so the value is
> always zero.
>
> On a PC99 architecture, there is always memory at physycal address zero;
> assume that a region that starts below 64k actually starts at zero,
> and use it for the mem_lower variable.
>
> Signed-off-by: Peter Chubb <peter.chubb@nicta.com.au>
Thanks Peter, I have applied this.
>
> ---
> kexec/arch/i386/kexec-multiboot-x86.c | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> Index: kexec-tools-2.0.4/kexec/arch/i386/kexec-multiboot-x86.c
> ===================================================================
> --- kexec-tools-2.0.4.orig/kexec/arch/i386/kexec-multiboot-x86.c 2013-03-14 18:45:16.000000000 +1000
> +++ kexec-tools-2.0.4/kexec/arch/i386/kexec-multiboot-x86.c 2014-01-15 10:21:02.138172304 +1000
> @@ -261,10 +261,18 @@ int multiboot_x86_load(int argc, char **
> mmap[i].length_high = length >> 32;
> if (range[i].type == RANGE_RAM) {
> mmap[i].Type = 1; /* RAM */
> - /* Is this the "low" memory? */
> - if ((range[i].start == 0)
> - && (range[i].end > mem_lower))
> + /*
> + * Is this the "low" memory? Can't just test
> + * against zero, because Linux protects (and
> + * hides) the first few pages of physical
> + * memory.
> + */
> +
> + if ((range[i].start <= 64*1024)
> + && (range[i].end > mem_lower)) {
> + range[i].start = 0;
> mem_lower = range[i].end;
> + }
> /* Is this the "high" memory? */
> if ((range[i].start <= 0x100000)
> && (range[i].end > mem_upper + 0x100000))
>
> --
> Dr Peter Chubb peter.chubb AT nicta.com.au
> http://www.ssrg.nicta.com.au Software Systems Research Group/NICTA
>
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2014-01-15 3:25 kexec-tools and multiboot breakage Peter Chubb
2014-01-15 3:48 ` Simon Horman
2014-01-15 21:39 ` [PATCH] Fix value of mbi->mem_lower for multiboot-x86 Peter Chubb
2014-01-16 0:22 ` Simon Horman
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