linux-kernel - Re: kexec, x86: Need a new e820 type support for kexec

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Message-ID: <20150819055906.GE19950@dhcp-128-28.nay.redhat.com>
Date:	Wed, 19 Aug 2015 13:59:06 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	linux-nvdimm@...1.01.org, kexec@...ts.infradead.org, hch@....de,
	linux-kernel@...r.kernel.org
Subject: Re: kexec, x86: Need a new e820 type support for kexec

On 08/18/15 at 11:36pm, Toshi Kani wrote:
> On 8/18/2015 8:53 PM, Baoquan He wrote:
> >On 08/18/15 at 09:01am, Toshi Kani wrote:
> >>On Tue, 2015-08-18 at 16:53 +0800, Baoquan He wrote:
> >>>Rethink it again, maybe it's better to pass PMEM as PRAM to kdump
> >>>kernel if user really want to use memmap way by specifying
> >>>--pass-memmap-cmdline. Then I need add the PMEM and PRAM checking here
> >>>you pointed out. Will repost with them.
> >>No, you should not report PMEM as PRAM.  They are different things.  The
> >>kdump kernel does not need to support memmap cmdline for PMEM, as the
> >>regular kernel does not -- memmap cmdline cannot emulate PMEM.
> >OK. Then it will be wrong if people intend to specify
> >--pass-memmap-cmdline. There might be 3 ways to fix this:
> >
> >1) add PMEM support in kernel. memmap cmdline is not only used for
> >emulating, but for kexec/kdump using.
> >
> >2) Delete --pass-memmap-cmdline option in kexec-tools since people
> >rarely use it.
> >
> >3) Add a note in kexec-tools that option --pass-memmap-cmdline can't
> >work together with PMEM, people should not use it.
> 
> 3) is fine, and I do not think we need a note either.  It does not
> make sense to add an memmap cmdline for PMEM since PMEM ranges
> require ACPI NFIT table.

OK, got it. Let me repost without PMEM memmap adding. In fact I am
a little confused that E820_PMEM is got by EFI in linux, seems in
do_add_efi_memmap() though later ACPI NFIT need be read and more
information about nvdimm will be got for nvdimm device. e820 memory map
need be got from uefi/bios/kexec, this doesn't conflict with ACPI NFIT
processing.

Thanks
Baoquan
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