[PATCH] Don't use /sys/firmware/memmap for Xen

[PATCH] Don't use /sys/firmware/memmap for Xen

[Bernhard Walle]

On Xen, we have to use /proc/iomem to retrieve the memory area for the kexec'd
kernel, not /sys/firmware/memmap. Dom0 kernel gets a E820 map that contains
only one region:

    0000000000000000-0000000018e5e000 (System RAM)

Compared to the /proc/iomem:

    00000000-0009cbff : System RAM
    0009cc00-0009ffff : reserved
    000ce000-000d3fff : reserved
    000e0000-000fffff : reserved
    00100000-1fd6ffff : System RAM
      01000000-04ffffff : Crash kernel
      1ec00000-1fbfffff : Hypervisor code and data
        1f0b4680-1f0b4873 : Crash note
        1f0b4900-1f0b4a93 : Crash note
        1f0b4b80-1f0b4d13 : Crash note
        1f0b4e00-1f0b4f93 : Crash note
    ...

Without that patch, /proc/vmcore is empty in the kexec'd kernel and I'm unable
to copy the crashdump.


Signed-off-by: Bernhard Walle <bwalle@suse.de>
---
 kexec/arch/i386/kexec-x86-common.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/kexec/arch/i386/kexec-x86-common.c b/kexec/arch/i386/kexec-x86-common.c
index 00c2be3..2112bd5 100644
--- a/kexec/arch/i386/kexec-x86-common.c
+++ b/kexec/arch/i386/kexec-x86-common.c
@@ -147,7 +147,14 @@ int get_memory_ranges(struct memory_range **range, int *ranges,
 {
 	int ret, i;
 
-	if (have_sys_firmware_memmap())
+	/*
+	 * When using Xen, /sys/firmware/memmap (i.e., the E820 map) is
+	 * wrong, it just provides one large memory are and that cannot
+	 * be used for Kdump. Use always the /proc/iomem interface there
+	 * even if we have /sys/firmware/memmap. Without that, /proc/vmcore
+	 * is empty in the kdump kernel.
+	 */
+	if (!xen_present() && have_sys_firmware_memmap())
 		ret = get_memory_ranges_sysfs(range, ranges);
 	else
 		ret = get_memory_ranges_proc_iomem(range, ranges);
-- 
1.6.0.2


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Re: [PATCH] Don't use /sys/firmware/memmap for Xen

[Bernhard Walle]

* Bernhard Walle [2008-11-25 13:49]:
>
> On Xen, we have to use /proc/iomem to retrieve the memory area for the kexec'd
> kernel, not /sys/firmware/memmap. Dom0 kernel gets a E820 map that contains
> only one region:
> 
>     0000000000000000-0000000018e5e000 (System RAM)

I just noticed that this has a compile warning. A fixed patch follows.


    Bernhard
-- 
Bernhard Walle, SUSE Linux Products GmbH, Architecture Development

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[PATCH] Don't use /sys/firmware/memmap for Xen

[Bernhard Walle]

On Xen, we have to use /proc/iomem to retrieve the memory area for the kexec'd
kernel, not /sys/firmware/memmap. Dom0 kernel gets a E820 map that contains
only one region:

    0000000000000000-0000000018e5e000 (System RAM)

Compared to the /proc/iomem:

    00000000-0009cbff : System RAM
    0009cc00-0009ffff : reserved
    000ce000-000d3fff : reserved
    000e0000-000fffff : reserved
    00100000-1fd6ffff : System RAM
      01000000-04ffffff : Crash kernel
      1ec00000-1fbfffff : Hypervisor code and data
        1f0b4680-1f0b4873 : Crash note
        1f0b4900-1f0b4a93 : Crash note
        1f0b4b80-1f0b4d13 : Crash note
        1f0b4e00-1f0b4f93 : Crash note
    ...

Without that patch, /proc/vmcore is empty in the kexec'd kernel and I'm unable
to copy the crashdump.


Signed-off-by: Bernhard Walle <bwalle@suse.de>
---
 kexec/arch/i386/kexec-x86-common.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/kexec/arch/i386/kexec-x86-common.c b/kexec/arch/i386/kexec-x86-common.c
index 00c2be3..1453780 100644
--- a/kexec/arch/i386/kexec-x86-common.c
+++ b/kexec/arch/i386/kexec-x86-common.c
@@ -27,6 +27,7 @@
 #include "../../kexec.h"
 #include "../../kexec-syscall.h"
 #include "../../firmware_memmap.h"
+#include "../../crashdump.h"
 #include "kexec-x86.h"
 
 static struct memory_range memory_range[MAX_MEMORY_RANGES];
@@ -147,7 +148,14 @@ int get_memory_ranges(struct memory_range **range, int *ranges,
 {
 	int ret, i;
 
-	if (have_sys_firmware_memmap())
+	/*
+	 * When using Xen, /sys/firmware/memmap (i.e., the E820 map) is
+	 * wrong, it just provides one large memory are and that cannot
+	 * be used for Kdump. Use always the /proc/iomem interface there
+	 * even if we have /sys/firmware/memmap. Without that, /proc/vmcore
+	 * is empty in the kdump kernel.
+	 */
+	if (!xen_present() && have_sys_firmware_memmap())
 		ret = get_memory_ranges_sysfs(range, ranges);
 	else
 		ret = get_memory_ranges_proc_iomem(range, ranges);
-- 
1.6.0.2


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Re: [PATCH] Don't use /sys/firmware/memmap for Xen

[Simon Horman]

On Wed, Nov 26, 2008 at 10:00:39AM +0100, Bernhard Walle wrote:
> On Xen, we have to use /proc/iomem to retrieve the memory area for the kexec'd
> kernel, not /sys/firmware/memmap. Dom0 kernel gets a E820 map that contains
> only one region:
> 
>     0000000000000000-0000000018e5e000 (System RAM)
> 
> Compared to the /proc/iomem:
> 
>     00000000-0009cbff : System RAM
>     0009cc00-0009ffff : reserved
>     000ce000-000d3fff : reserved
>     000e0000-000fffff : reserved
>     00100000-1fd6ffff : System RAM
>       01000000-04ffffff : Crash kernel
>       1ec00000-1fbfffff : Hypervisor code and data
>         1f0b4680-1f0b4873 : Crash note
>         1f0b4900-1f0b4a93 : Crash note
>         1f0b4b80-1f0b4d13 : Crash note
>         1f0b4e00-1f0b4f93 : Crash note
>     ...
> 
> Without that patch, /proc/vmcore is empty in the kexec'd kernel and I'm unable
> to copy the crashdump.

Thanks Bernhard, applied.

-- 
Simon Horman
  VA Linux Systems Japan K.K., Sydney, Australia Satellite Office
  H: www.vergenet.net/~horms/             W: www.valinux.co.jp/en


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