linux-kernel - [PATCH 1/2] x86: Make E820_X_MAX unconditionally larger than E820MAX

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Date:   Tue, 29 Nov 2016 21:24:46 -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>,
        Ingo Molnar <mingo@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>, x86@...nel.org,
        xen-devel@...ts.xenproject.org
Subject: [PATCH 1/2] x86: Make E820_X_MAX unconditionally larger than E820MAX

It's really not necessary to limit E820_X_MAX to 128 in the non-EFI
case.  This commit drops E820_X_MAX's dependency on CONFIG_EFI, so that
E820_X_MAX is always at least slightly larger than E820MAX.

The real motivation behind this is actually to prevent some issues in
the Xen kernel, where the XENMEM_machine_memory_map hypercall can
produce an e820 map larger than 128 entries, even on systems where the
original e820 table was quite a bit smaller than that, depending on how
many IOAPICs are installed on the system.

Signed-off-by: Alex Thorlton <athorlton@....com>
Suggested-by: Ingo Molnar <mingo@...hat.com>
Cc: Russ Anderson <rja@....com>
Cc: David Vrabel <david.vrabel@...rix.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: x86@...nel.org
Cc: xen-devel@...ts.xenproject.org
---
 arch/x86/include/asm/e820.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/e820.h b/arch/x86/include/asm/e820.h
index 476b574..aa00d33 100644
--- a/arch/x86/include/asm/e820.h
+++ b/arch/x86/include/asm/e820.h
@@ -1,13 +1,15 @@
 #ifndef _ASM_X86_E820_H
 #define _ASM_X86_E820_H
 
-#ifdef CONFIG_EFI
+/*
+ * We need to make sure that E820_X_MAX is defined
+ * before we include uapi/asm/e820.h
+ */
 #include <linux/numa.h>
 #define E820_X_MAX (E820MAX + 3 * MAX_NUMNODES)
-#else	/* ! CONFIG_EFI */
-#define E820_X_MAX E820MAX
-#endif
+
 #include <uapi/asm/e820.h>
+
 #ifndef __ASSEMBLY__
 /* see comment in arch/x86/kernel/e820.c */
 extern struct e820map *e820;
-- 
1.8.5.6