linux-kernel - [RFC PATCH] xen/x86: Increase xen_e820_map to E820_X

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Date:   Mon, 14 Nov 2016 18:11:16 -0600
From:   Alex Thorlton <athorlton@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Alex Thorlton <athorlton@....com>, Russ Anderson <rja@....com>,
        David Vrabel <david.vrabel@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        xen-devel@...ts.xenproject.org
Subject: [RFC PATCH] xen/x86: Increase xen_e820_map to E820_X_MAX possible entries

Hey everyone,

We're having problems with large systems hitting a BUG in
xen_memory_setup, due to extra e820 entries created in the
XENMEM_machine_memory_map callback.  The change in the patch gets things
working, but Boris and I wanted to get opinions on whether or not this
is the appropriate/entire solution, which is why I've sent it as an RFC
for now.

Boris pointed out to me that E820_X_MAX is only large when CONFIG_EFI=y,
which is a detail worth discussig.  He proposed possibly adding
CONFIG_XEN to the conditions under which we set E820_X_MAX to a larger
value than E820MAX, since the Xen e820 table isn't bound by the
zero-page memory limitations.

I do *slightly* question the use of E820_X_MAX here, only from a
cosmetic prospective, as I believe this macro is intended to describe
the maximum size of the extended e820 table, which, AFAIK, is not used
by the Xen HV.  That being said, there isn't exactly a "more
appropriate" macro/variable to use, so this may not really be an issue.

Any input on the patch, or the questions I've raised above is greatly
appreciated!

- Alex

Alex Thorlton (1):
  xen/x86: Increase xen_e820_map to E820_X_MAX possible entries

 arch/x86/xen/setup.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

-- 
1.8.5.6