Re: devm_memremap_pages() triggers a kasan_add_zero_shadow() warning

[Dan Williams <dan.j.williams@intel.com>]

On Sat, Aug 17, 2019 at 4:13 AM Qian Cai <cai@lca.pw> wrote:
>
>
>
> > On Aug 16, 2019, at 11:57 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> >
> > On Fri, Aug 16, 2019 at 8:34 PM Qian Cai <cai@lca.pw> wrote:
> >>
> >>
> >>
> >>> On Aug 16, 2019, at 5:48 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> >>>
> >>> On Fri, Aug 16, 2019 at 2:36 PM Qian Cai <cai@lca.pw> 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 “There seems to be an issue with CONFIG_KSAN at the moment however.”
> without more detail though.

Does disabling CONFIG_RANDOMIZE_BASE help? Maybe that workaround has
regressed. Effectively we need to find what is causing the kernel to
sometimes be placed in the middle of a custom reserved memmap= range.