/proc/vmcore mmap() failure issue

[Vivek Goyal]

[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.

Thanks
Vivek

On Wed, Nov 13, 2013 at 03:41:30PM -0500, Vivek Goyal wrote:
> Hi Hatayama,
> 
> We are facing some /proc/vmcore mmap() failure issues and then makdumpfile
> exits without saving dump and system reboots.
> 
> I tried latest makedumpfile (devel branch) with 3.12 kernel.
> 
> I think this issue happens only on some machines. And it looks like it
> happens when end of system RAM chunk in first kernel is not page aligned. For
> example, I have one machine where I noticed it and this is how system
> RAM looks like.
> 
> 00100000-dafa57ff : System RAM
>   01000000-015892fa : Kernel code
>   015892fb-0195c9ff : Kernel data
>   01ae6000-01d31fff : Kernel bss
>   24000000-33ffffff : Crash kernel
> dafa5800-dbffffff : reserved
> 
> Notice that dafa57ff does not end at page boundary and next reserved
> range does not start at page boundary. I think that next reserved
> range is referenced through some ACPI data. More on this later.
> 
> So we put some printk() messages to get more info. In a nut shell,
> remap_pfn_range() fails when we try to map the last section of system
> RAM not ending on page boundary.
> 
> remap_pfn_range()
>    track_pfn_remap() {
>         /*
>          * For anything smaller than the vma size we set prot based on the
>          * lookup.
>          */ 
>         flags = lookup_memtype(paddr);
>         
>         /* Check memtype for the remaining pages */
>         while (size > PAGE_SIZE) {
>                 size -= PAGE_SIZE;
>                 paddr += PAGE_SIZE;
>                 if (flags != lookup_memtype(paddr))
>                         return -EINVAL; <---------------- Failure.
>         }
> 	
>    }
>      
> 
> So we pass in a range to track_pfn_remap. Say pfn=0xdad62 size=0x244000.
> Now we call lookup_memtype() on every page in the range and make sure
> they all are same, otherwise we fail. Guess what, all all same except
> last page (which does not end at page boundary).
> 
> I dived deeper in to lookup_memtype() and noticed that all regular
> ranges are not registered anywhere and their flags are _PAGE_CACHE_UC_MINUS.
> But last unaligned page/range, is registered in memtype rb tree and
> has attribute, _PAGE_CACHE_WB.
> 
> Then I hooked into reserve_memtype() to figure out who is registering
> page 0xdafa5000 and it is acpi_init() which does it.
> 
> [    0.721655] Hardware name: <edited>
> [    0.730590]  ffff8800340f3830 ffff8800340f37c0 ffffffff81575509
> 00000000dafa5000
> [    0.738010]  ffff8800340f3800 ffffffff810566cc 00000000000dafa5
> 00000000dafa5000
> [    0.745428]  00000000dafa6000 00000000dafa5000 0000000000000000
> 0000000000001000
> [    0.752845] Call Trace:
> [    0.755288]  [<ffffffff81575509>] dump_stack+0x45/0x56
> [    0.760414]  [<ffffffff810566cc>] reserve_memtype+0x31c/0x3f0
> [    0.766144]  [<ffffffff810537ef>] __ioremap_caller+0x12f/0x360
> [    0.771963]  [<ffffffff8130ad56>] ? acpi_os_release_object+0xe/0x12
> [    0.778217]  [<ffffffff815686ba>] ? acpi_os_map_memory+0xf6/0x14e
> [    0.784295]  [<ffffffff81053a54>] ioremap_cache+0x14/0x20
> [    0.789679]  [<ffffffff815686ba>] acpi_os_map_memory+0xf6/0x14e
> [    0.795582]  [<ffffffff81322ac9>]
> acpi_ex_system_memory_space_handler+0xdd/0x1ca
> [    0.802961]  [<ffffffff8131ca48>]
> acpi_ev_address_space_dispatch+0x1b0/0x208
> [    0.809993]  [<ffffffff8131fd49>] acpi_ex_access_region+0x20e/0x2a2
> [    0.816244]  [<ffffffff81149464>] ? __alloc_pages_nodemask+0x134/0x300
> [    0.822754]  [<ffffffff813200e4>] acpi_ex_field_datum_io+0xf6/0x171
> [    0.829004]  [<ffffffff81320301>] acpi_ex_extract_from_field+0xd7/0x20a
> [    0.835602]  [<ffffffff81331d80>] ?
> acpi_ut_create_internal_object_dbg+0x23/0x8a
> [    0.842981]  [<ffffffff8131f8e7>]
> acpi_ex_read_data_from_field+0x10f/0x14b
> [    0.849838]  [<ffffffff81322e16>]
> acpi_ex_resolve_node_to_value+0x18e/0x21c
> [    0.856780]  [<ffffffff813230a6>] acpi_ex_resolve_to_value+0x202/0x209
> [    0.863291]  [<ffffffff81319486>] acpi_ds_evaluate_name_path+0x7b/0xf5
> [    0.869803]  [<ffffffff81319834>] acpi_ds_exec_end_op+0x98/0x3e8
> [    0.875793]  [<ffffffff8132aca4>] acpi_ps_parse_loop+0x514/0x560
> [    0.881784]  [<ffffffff8132b738>] acpi_ps_parse_aml+0x98/0x28c
> [    0.887601]  [<ffffffff8132bf8d>] acpi_ps_execute_method+0x1c1/0x26c
> [    0.893939]  [<ffffffff813269c5>] acpi_ns_evaluate+0x1c1/0x258
> [    0.899755]  [<ffffffff8131cb98>] acpi_ev_execute_reg_method+0xca/0x112
> [    0.906353]  [<ffffffff8131cd6e>] acpi_ev_reg_run+0x48/0x52
> [    0.911910]  [<ffffffff81328fad>] acpi_ns_walk_namespace+0xc8/0x17f
> [    0.918160]  [<ffffffff8131cd26>] ? acpi_ev_detach_region+0x146/0x146
> [    0.924585]  [<ffffffff8131cdbc>] acpi_ev_execute_reg_methods+0x44/0xf7
> [    0.931184]  [<ffffffff819b2324>] ? acpi_sleep_proc_init+0x2a/0x2a
> [    0.937349]  [<ffffffff8130ac66>] ? acpi_os_wait_semaphore+0x43/0x57
> [    0.943686]  [<ffffffff81331a3f>] ? acpi_ut_acquire_mutex+0x48/0x88
> [    0.949938]  [<ffffffff8131ceb8>]
> acpi_ev_initialize_op_regions+0x49/0x71
> [    0.956709]  [<ffffffff819b2324>] ? acpi_sleep_proc_init+0x2a/0x2a
> [    0.962873]  [<ffffffff81333310>] acpi_initialize_objects+0x23/0x4f
> [    0.969125]  [<ffffffff819b23b4>] acpi_init+0x90/0x268
> 
> So basically, this split page seems to be a problem. Some other code
> thinks that it has access to full page and goes ahead and registers
> that with PAT rb tree and this causes problems in mmap() code.
> 
> I suspect we might have to go back to idea of copying first and last
> non page aligned ranges in new kernel's memory and read it from there
> to solve this issue. Do you have other ideas?
> 
> Thanks
> Vivek