[PATCH] kexec/x86: Do not map crash kernel area

[PATCH] kexec/x86: Do not map crash kernel area

[Daniel Kiper]

Do not map crash kernel area. This mapping is not in use anymore.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 xen/arch/x86/setup.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index f07ee2b..4833ca3 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1097,9 +1097,7 @@ void __init __start_xen(unsigned long mbi_p)
                          mod[i].mod_start,
                          PFN_UP(mod[i].mod_end), PAGE_HYPERVISOR);
     }
-    map_pages_to_xen((unsigned long)__va(kexec_crash_area.start),
-                     kexec_crash_area.start >> PAGE_SHIFT,
-                     PFN_UP(kexec_crash_area.size), PAGE_HYPERVISOR);
+
     xen_virt_end = ((unsigned long)_end + (1UL << L2_PAGETABLE_SHIFT) - 1) &
                    ~((1UL << L2_PAGETABLE_SHIFT) - 1);
     destroy_xen_mappings(xen_virt_end, XEN_VIRT_START + BOOTSTRAP_MAP_BASE);
-- 
1.7.10.4

Re: [PATCH] kexec/x86: Do not map crash kernel area

[David Vrabel]

On 09/12/2013 18:01, Daniel Kiper wrote:
> Do not map crash kernel area. This mapping is not in use anymore.
> 
> Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>

Acked-by: David Vrabel <david.vrabel@citrix.com>

However, this isn't a bug fix so I don't think it's suitable 4.4 now.

David

Re: [PATCH] kexec/x86: Do not map crash kernel area

[Jan Beulich]

>>> On 09.12.13 at 19:16, David Vrabel <dvrabel@cantab.net> wrote:
> On 09/12/2013 18:01, Daniel Kiper wrote:
>> Do not map crash kernel area. This mapping is not in use anymore.
>> 
>> Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
> 
> Acked-by: David Vrabel <david.vrabel@citrix.com>
> 
> However, this isn't a bug fix so I don't think it's suitable 4.4 now.

I think this is quite clearly a bug fix, taking into consideration our
earlier discussion about systems with more memory  (16Tb if the
physical address map is mostly contiguous) than Xen can handle.

Jan

Re: [PATCH] kexec/x86: Do not map crash kernel area

[Jan Beulich]

>>> On 09.12.13 at 19:01, Daniel Kiper <daniel.kiper@oracle.com> wrote:
> Do not map crash kernel area. This mapping is not in use anymore.

That description to me reads like it was used before. Was it really?
I think the issue of it possibly being outside of mappable memory
has been in existence for quite a while, and hence with the
description being worded in that way this would be a suitable
trigger for backporting to the stable trees.

Jan

> Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
> ---
>  xen/arch/x86/setup.c |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> index f07ee2b..4833ca3 100644
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -1097,9 +1097,7 @@ void __init __start_xen(unsigned long mbi_p)
>                           mod[i].mod_start,
>                           PFN_UP(mod[i].mod_end), PAGE_HYPERVISOR);
>      }
> -    map_pages_to_xen((unsigned long)__va(kexec_crash_area.start),
> -                     kexec_crash_area.start >> PAGE_SHIFT,
> -                     PFN_UP(kexec_crash_area.size), PAGE_HYPERVISOR);
> +
>      xen_virt_end = ((unsigned long)_end + (1UL << L2_PAGETABLE_SHIFT) - 1) &
>                     ~((1UL << L2_PAGETABLE_SHIFT) - 1);
>      destroy_xen_mappings(xen_virt_end, XEN_VIRT_START + 
> BOOTSTRAP_MAP_BASE);
> -- 
> 1.7.10.4

Re: [PATCH] kexec/x86: Do not map crash kernel area

[Daniel Kiper]

On Tue, Dec 10, 2013 at 08:22:29AM +0000, Jan Beulich wrote:
> >>> On 09.12.13 at 19:01, Daniel Kiper <daniel.kiper@oracle.com> wrote:
> > Do not map crash kernel area. This mapping is not in use anymore.
>
> That description to me reads like it was used before. Was it really?

Probably it was done deliberately but I could not find any references
to this mapping in old kexec code or description in commit messages
why it was done. Or maybe it was mistake...

> I think the issue of it possibly being outside of mappable memory
> has been in existence for quite a while, and hence with the
> description being worded in that way this would be a suitable
> trigger for backporting to the stable trees.

I have done kexec/kdump tests on Xen 4.3.1 without that mapping
and it works without any issue. Hence, I think that we could
backport it safely at least to Xen 4.3. However, I suppose that
it should also work for Xen 4.2.

Daniel

Re: [PATCH] kexec/x86: Do not map crash kernel area

[David Vrabel]

On 10/12/13 08:19, Jan Beulich wrote:
>>>> On 09.12.13 at 19:16, David Vrabel <dvrabel@cantab.net> wrote:
>> On 09/12/2013 18:01, Daniel Kiper wrote:
>>> Do not map crash kernel area. This mapping is not in use anymore.
>>>
>>> Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
>>
>> Acked-by: David Vrabel <david.vrabel@citrix.com>
>>
>> However, this isn't a bug fix so I don't think it's suitable 4.4 now.
> 
> I think this is quite clearly a bug fix, taking into consideration our
> earlier discussion about systems with more memory  (16Tb if the
> physical address map is mostly contiguous) than Xen can handle.

Oh yes, of course. I'd forgotten about that.

David

Re: [PATCH] kexec/x86: Do not map crash kernel area

[Jan Beulich]

>>> On 10.12.13 at 13:50, Daniel Kiper <daniel.kiper@oracle.com> wrote:
> On Tue, Dec 10, 2013 at 08:22:29AM +0000, Jan Beulich wrote:
>> >>> On 09.12.13 at 19:01, Daniel Kiper <daniel.kiper@oracle.com> wrote:
>> > Do not map crash kernel area. This mapping is not in use anymore.
>>
>> That description to me reads like it was used before. Was it really?
> 
> Probably it was done deliberately but I could not find any references
> to this mapping in old kexec code or description in commit messages
> why it was done. Or maybe it was mistake...

Could I ask you then to resend with a more appropriate description?

Jan