Re: [pmem_attach_disk] WARNING: CPU: 46 PID: 518 at kernel/memremap.c:363 devm_memremap_pages+0x350/0x4b0

[Fengguang Wu]

CC Ying and Aaron for Dan's tips on nvdimm testing.

On Mon, Oct 30, 2017 at 05:24:42PM -0700, Dan Williams wrote:
> On Mon, Oct 30, 2017 at 5:00 PM, Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote:
> > Hi Dan,
> >
> > On Mon, Oct 30, 2017 at 08:59:46AM -0700, Dan Williams wrote:
> > > On Mon, Oct 30, 2017 at 12:40 AM, Fengguang Wu <fengguang.wu@xxxxxxxxx>
> > > wrote:
> > > > CC nvdimm maintainers.
> > > >
> > > > On Sun, Oct 29, 2017 at 11:51:55PM +0100, Fengguang Wu wrote:
> > > > > Hi Linus,
> > > > >
> > > > > Up to now we see the below boot error/warnings when testing v4.14-rc6.
> > > > >
> > > > > They hit the RC release mainly due to various imperfections in 0day's
> > > > > auto bisection. So I manually list them here and CC the likely easy to
> > > > > debug ones to the corresponding maintainers in the followup emails.
> > > > >
> > > > > boot_successes: 4700
> > > > > boot_failures: 247
> > > >
> > > >
> > > >
> > > > [...]
> > > >
> > > > > WARNING:at_kernel/memremap.c:#devm_memremap_pages: 1
> > > >
> > > >
> > > >
> > > > Bisect failed, hope it's not hard to debug:
> > > >
> > > >         Start
> > > > [   18.989316] devm_memremap_pages attempted on mixed region [mem
> > > > 0x680000000-0x103dffffff flags 0x200]
> > >
> > >
> > >
> > > This appears to be a problem in the test environment. "Persistent
> > > Memory" can only be specified on a minimum of a 128MB boundary if it
> > > intersects "System RAM". Assuming I did my math right this appears to
> > > end on 16MB boundary. Fixing this problem in the kernel would require
> > > this patch set:
> > >
> > >    "mm: sub-section memory hotplug support":
> > > https://lwn.net/Articles/707908/
> >
> >
> > Good to know that!
> >
> > > ...but I have abandoned / pushed that to the back of my queue since
> > > BIOS induced version of this problem does not appear to trigger in
> > > practice. I assume this test is using memmap=ss!nn?
> >
> >
> > Yes, we used
> >
> >        memmap=104G!26G memmap=104G!154G
> > The warning showed up only once -- attached is the full dmesg.
>
> Something is going wrong with memmap= because you are not getting 1G
> aligned address ranges. I think you would have better luck switching
> to the official nvdimm emulation in qemu-kvm rather than relying on
> memmap= which is just a fragile / unreliable interface. In fact we
> should look to deprecate it and point everyone to use the standard
> methods. We just have a problem of legacy pre-ACPI6 platforms that
> have no other way than a kernel command line to identify persistent
> memory ranges.

Got it. Thank you for the tips!

Thanks,
Fengguang