Re: devm_memremap_pages() triggers a kasan_add_zero_shadow() warning

[Qian Cai]

> On Aug 16, 2019, at 11:57 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> 
> On Fri, Aug 16, 2019 at 8:34 PM Qian Cai <cai@xxxxxx> wrote:
>> 
>> 
>> 
>>> On Aug 16, 2019, at 5:48 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>>> 
>>> On Fri, Aug 16, 2019 at 2:36 PM Qian Cai <cai@xxxxxx> wrote:
>>>> 
>>>> Every so often recently, booting Intel CPU server on linux-next triggers this
>>>> warning. Trying to figure out if  the commit 7cc7867fb061
>>>> ("mm/devm_memremap_pages: enable sub-section remap") is the culprit here.
>>>> 
>>>> # ./scripts/faddr2line vmlinux devm_memremap_pages+0x894/0xc70
>>>> devm_memremap_pages+0x894/0xc70:
>>>> devm_memremap_pages at mm/memremap.c:307
>>> 
>>> Previously the forced section alignment in devm_memremap_pages() would
>>> cause the implementation to never violate the KASAN_SHADOW_SCALE_SIZE
>>> (12K on x86) constraint.
>>> 
>>> Can you provide a dump of /proc/iomem? I'm curious what resource is
>>> triggering such a small alignment granularity.
>> 
>> This is with memmap=4G!4G ,
>> 
>> # cat /proc/iomem
> [..]
>> 100000000-155dfffff : Persistent Memory (legacy)
>>  100000000-155dfffff : namespace0.0
>> 155e00000-15982bfff : System RAM
>>  155e00000-156a00fa0 : Kernel code
>>  156a00fa1-15765d67f : Kernel data
>>  157837000-1597fffff : Kernel bss
>> 15982c000-1ffffffff : Persistent Memory (legacy)
>> 200000000-87fffffff : System RAM
> 
> Ok, looks like 4G is bad choice to land the pmem emulation on this
> system because it collides with where the kernel is deployed and gets
> broken into tiny pieces that violate kasan's. This is a known problem
> with memmap=. You need to pick an memory range that does not collide
> with anything else. See:
> 
>    https://nvdimm.wiki.kernel.org/how_to_choose_the_correct_memmap_kernel_parameter_for_pmem_on_your_system
> 
> ...for more info.

Well, it seems I did exactly follow the information in that link,

[    0.000000] BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x0000000000093fff] usable
[    0.000000] BIOS-e820: [mem 0x0000000000094000-0x000000000009ffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000000e0000-0x00000000000fffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000005a7a0fff] usable
[    0.000000] BIOS-e820: [mem 0x000000005a7a1000-0x000000005b5e0fff] reserved
[    0.000000] BIOS-e820: [mem 0x000000005b5e1000-0x00000000790fefff] usable
[    0.000000] BIOS-e820: [mem 0x00000000790ff000-0x00000000791fefff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000791ff000-0x000000007b5fefff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x000000007b5ff000-0x000000007b7fefff] ACPI data
[    0.000000] BIOS-e820: [mem 0x000000007b7ff000-0x000000007b7fffff] usable
[    0.000000] BIOS-e820: [mem 0x000000007b800000-0x000000008fffffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000ff800000-0x00000000ffffffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000087fffffff] usable

Where 4G is good. Then,

[    0.000000] user-defined physical RAM map:
[    0.000000] user: [mem 0x0000000000000000-0x0000000000093fff] usable
[    0.000000] user: [mem 0x0000000000094000-0x000000000009ffff] reserved
[    0.000000] user: [mem 0x00000000000e0000-0x00000000000fffff] reserved
[    0.000000] user: [mem 0x0000000000100000-0x000000005a7a0fff] usable
[    0.000000] user: [mem 0x000000005a7a1000-0x000000005b5e0fff] reserved
[    0.000000] user: [mem 0x000000005b5e1000-0x00000000790fefff] usable
[    0.000000] user: [mem 0x00000000790ff000-0x00000000791fefff] reserved
[    0.000000] user: [mem 0x00000000791ff000-0x000000007b5fefff] ACPI NVS
[    0.000000] user: [mem 0x000000007b5ff000-0x000000007b7fefff] ACPI data
[    0.000000] user: [mem 0x000000007b7ff000-0x000000007b7fffff] usable
[    0.000000] user: [mem 0x000000007b800000-0x000000008fffffff] reserved
[    0.000000] user: [mem 0x00000000ff800000-0x00000000ffffffff] reserved
[    0.000000] user: [mem 0x0000000100000000-0x00000001ffffffff] persistent (type 12)
[    0.000000] user: [mem 0x0000000200000000-0x000000087fffffff] usable

The doc did mention that âThere seems to be an issue with CONFIG_KSAN at the moment however.â
without more detail though.