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From: Jeff Moyer <jmoyer@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: x86@kernel.org, Boaz Harrosh <boaz@plexistor.com>,
        linux-nvdimm@ml01.01.org, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Zhang Yi <yizhan@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] x86: fix kdump, cleanup aborted E820_PRAM max_pfn manipulation
References: <147448744538.34910.11287693517367139607.stgit@dwillia2-desk3.amr.corp.intel.com>
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Date: Wed, 21 Sep 2016 16:22:31 -0400
In-Reply-To: <147448744538.34910.11287693517367139607.stgit@dwillia2-desk3.amr.corp.intel.com>
        (Dan Williams's message of "Wed, 21 Sep 2016 12:50:45 -0700")
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Dan Williams <dan.j.williams@intel.com> writes:

> In commit ec776ef6bbe1 "x86/mm: Add support for the non-standard
> protected e820 type" Christoph references the original patch I wrote
> implementing pmem support.  The intent of the 'max_pfn' changes in that
> commit were to enable persistent memory ranges to be covered by the
> struct page memmap by default.  However, that approach was abandoned
> when Christoph ported the patches [1], and that functionality has since
> been replaced by devm_memremap_pages().
>
> In the meantime, this max_pfn manipulation is confusing kdump [2] that
> assumes that everything covered by the max_pfn is "System RAM".  This
> results in kdump hanging or crashing.

That was my assumption, I'm not certain that the kdump code is assuming
the pmem region is usable as RAM.  The end result is a hung kdump
kernel.

> [1]: https://lists.01.org/pipermail/linux-nvdimm/2015-March/000348.html
> [2]: https://bugzilla.redhat.com/show_bug.cgi?id=1351098
>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Boaz Harrosh <boaz@plexistor.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Reported-by: Zhang Yi <yizhan@redhat.com>
> Reported-by: Jeff Moyer <jmoyer@redhat.com>
> Tested-by: Zhang Yi <yizhan@redhat.com>

I actually did the testing.  You can leave that line as is, though, as
I'm sure Yi will also test it.  :)

> Fixes: ec776ef6bbe1 ("x86/mm: Add support for the non-standard protected e820 type")
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

Thanks, Dan!

-Jeff