[Makedumpfile PATCH V2 2/4] x86_64: translate all VA to PA using page table values

[Atsushi Kumagai]

>On 12/12/16 at 08:40am, Atsushi Kumagai wrote:
>> >On Saturday 10 December 2016 07:03 AM, bhe at redhat.com wrote:
>> >> On 12/10/16 at 09:29am, Baoquan He wrote:
>> >>> On 12/09/16 at 10:25pm, Baoquan He wrote:
>> >>>> On 12/09/16 at 03:40pm, Pratyush Anand wrote:
>> >>>>>>> -	page_dir  = SYMBOL(init_level4_pgt);
>> >>>>>>> +	page_dir = SYMBOL(init_level4_pgt) - __START_KERNEL_map + phys_base;
>> >>>>>>
>> >>>>>> I found that this change breaks the backward compatibility for
>> >>>>>> kernel 2.6.21 or older since phys_base was introduced in kernel 2.6.22
>> >>>>>> by the commit below:
>> >>>>>>
>> >>>>>>   commit 1ab60e0f72f71ec54831e525a3e1154f1c092408
>> >>>>>>   Author: Vivek Goyal <vgoyal at in.ibm.com>
>> >>>>>>   Date:   Wed May 2 19:27:07 2007 +0200
>> >>>>>>
>> >>>>>>       [PATCH] x86-64: Relocatable Kernel Support
>> >>>>>>
>> >>>>>> There is no problem if phys_base is always 0 in older kernel, but
>> >>>>>> get_phys_base_x86_64() calculates "phys_base = 0x100000" from my vmcore:
>> >>>>
>> >>>> This is really awkward. Checked code, found PAGE_OFFSET is
>> >>>> 0xffff810000000000 before 2.6.26, then changed to 0xffff880000000000
>> >>>> after that. Can we check the page_offset calculated from pt_load
>> >>>> segments, meanwhile check if has VMCOREINFO and osrelease after 2.6.21.
>> >>>>
>> >>>> With both of above condition, we could set phys_vase to 0. Not sure if
>> >>>> this can solve the existing problem.
>> >>>
>> >>> I meant making a judgement:
>> >>>
>> >>
>> >> Sorry, should be:
>> >> if (page_offset == 0xffff810000000000 && !info->kernel_version > KERNEL_VERSION(2, 6, 21))
>> >> 	info->phys_base = 0;
>> >>
>> >
>> >
>> >But you can not read kernel_version because those version does not have
>> >VMCOREINFO. So, has_vmcoreinfo() still need to be used.
>>
>> Thanks for your comments, using has_vmcoreinfo() sounds like a good approach,
>> but not perfect way. VMCOREINFO has been introduced since 2.6.24,
>> 2.6.22 and 2.6.23 don't have VMCOREINFO but have phys_base.
>>
>> Conversely, 2.6.22 and 2.6.23 require vmlinux, so we can confirm the existence of
>> phys_base with that. My idea is:
>>
>> diff --git a/arch/x86_64.c b/arch/x86_64.c
>> index 010ea10..893cd51 100644
>> --- a/arch/x86_64.c
>> +++ b/arch/x86_64.c
>> @@ -67,6 +67,14 @@ get_phys_base_x86_64(void)
>>                 return TRUE;
>>         }
>>
>> +       /* linux-2.6.21 or older don't have phys_base, should be set to 0. */
>> +       if (!has_vmcoreinfo()) {
>> +               SYMBOL_INIT(phys_base, "phys_base");
>> +               if (SYMBOL(phys_base) == NOT_FOUND_SYMBOL) {
>> +                       return TRUE;
>> +               }
>> +       }
>> +
>>         for (i = 0; get_pt_load(i, &phys_start, NULL, &virt_start, NULL); i++) {
>>                 if (virt_start >= __START_KERNEL_map) {
>>
>>
>> This fix may resolve my issue, but now I have another question that
>> "Is the logic of get_phys_base_x86_64() correct in any kernel configuration ?"
>> I mean I'm worried about the possibility that another offset gets mixed with
>> the result of get_phys_base_x86_64() like my 2.6.21 case.
>> After phys_base was introduced, does it always equal to the offset which can be
>> calculated from PT_LOAD headers ?
>
>Don't worry. phys_base was introduced just after 2.6.21.
>
>commit 1ab60e0f72f71ec54831e525a3e1154f1c092408
>Author: Vivek Goyal <vgoyal at in.ibm.com>
>Date:   Wed May 2 19:27:07 2007 +0200
>
>    [PATCH] x86-64: Relocatable Kernel Support
>
>[bhe at x1 linux]$ git describe 1ab60e0f72f71ec54831e525a3e1154f1c092408
>v2.6.21-1836-g1ab60e0

All right, thanks.
I'll release v1.6.1 soon if there is nothing wrong with the retest.

Regards,
Atsushi Kumagai