linux-kernel - [tip:x86/boot] x86/init: Use a platform legacy quirk for EBDA

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Date:	Fri, 22 Apr 2016 02:51:06 -0700
From:	"tip-bot for Luis R. Rodriguez" <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	dvlasenk@...hat.com, bp@...en8.de, peterz@...radead.org,
	hpa@...or.com, brgerst@...il.com, mcgrof@...nel.org,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	mingo@...nel.org, linux-kernel@...r.kernel.org, luto@...capital.net
Subject: [tip:x86/boot] x86/init: Use a platform legacy quirk for EBDA

Commit-ID:  1330e3bc544a1951d81b7f3c7d4cecf77d906f67
Gitweb:     http://git.kernel.org/tip/1330e3bc544a1951d81b7f3c7d4cecf77d906f67
Author:     Luis R. Rodriguez <mcgrof@...nel.org>
AuthorDate: Wed, 13 Apr 2016 17:04:36 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 22 Apr 2016 10:29:02 +0200

x86/init: Use a platform legacy quirk for EBDA

This replaces the paravirt_enabled() check with a
proper x86 legacy platform quirk.

As per 0-day, this bumps the vmlinux size using i386-tinyconfig as
follows:

TOTAL   TEXT   init.text   x86_early_init_platform_quirks()
+39     +35    +35         +25

That's a 4 byte total overhead, the rest is all cleared out
upon init as its all __init text.

v2: document 0-day vmlinux size impact

Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: andrew.cooper3@...rix.com
Cc: andriy.shevchenko@...ux.intel.com
Cc: bigeasy@...utronix.de
Cc: boris.ostrovsky@...cle.com
Cc: david.vrabel@...rix.com
Cc: ffainelli@...ebox.fr
Cc: george.dunlap@...rix.com
Cc: glin@...e.com
Cc: jgross@...e.com
Cc: jlee@...e.com
Cc: josh@...htriplett.org
Cc: julien.grall@...aro.org
Cc: konrad.wilk@...cle.com
Cc: kozerkov@...allels.com
Cc: lenb@...nel.org
Cc: lguest@...ts.ozlabs.org
Cc: linux-acpi@...r.kernel.org
Cc: lv.zheng@...el.com
Cc: matt@...eblueprint.co.uk
Cc: mbizon@...ebox.fr
Cc: rjw@...ysocki.net
Cc: robert.moore@...el.com
Cc: rusty@...tcorp.com.au
Cc: tiwai@...e.de
Cc: toshi.kani@...com
Cc: xen-devel@...ts.xensource.com
Link: http://lkml.kernel.org/r/1460592286-300-7-git-send-email-mcgrof@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/x86_init.h   | 3 +++
 arch/x86/kernel/head.c            | 2 +-
 arch/x86/kernel/platform-quirks.c | 4 ++++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 8bb8c1a..89d9d57 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -145,9 +145,12 @@ struct timespec;
  * struct x86_legacy_features - legacy x86 features
  *
  * @rtc: this device has a CMOS real-time clock present
+ * @ebda_search: it's safe to search for the EBDA signature in the hardware's
+ * 	low RAM
  */
 struct x86_legacy_features {
 	int rtc;
+	int ebda_search;
 };
 
 /**
diff --git a/arch/x86/kernel/head.c b/arch/x86/kernel/head.c
index 992f442..afe65df 100644
--- a/arch/x86/kernel/head.c
+++ b/arch/x86/kernel/head.c
@@ -38,7 +38,7 @@ void __init reserve_ebda_region(void)
 	 * that the paravirt case can handle memory setup
 	 * correctly, without our help.
 	 */
-	if (paravirt_enabled())
+	if (!x86_platform.legacy.ebda_search)
 		return;
 
 	/* end of low (conventional) memory */
diff --git a/arch/x86/kernel/platform-quirks.c b/arch/x86/kernel/platform-quirks.c
index 021a5f9..01b1597 100644
--- a/arch/x86/kernel/platform-quirks.c
+++ b/arch/x86/kernel/platform-quirks.c
@@ -7,8 +7,12 @@
 void __init x86_early_init_platform_quirks(void)
 {
 	x86_platform.legacy.rtc = 1;
+	x86_platform.legacy.ebda_search = 0;
 
 	switch (boot_params.hdr.hardware_subarch) {
+	case X86_SUBARCH_PC:
+		x86_platform.legacy.ebda_search = 1;
+		break;
 	case X86_SUBARCH_XEN:
 	case X86_SUBARCH_LGUEST:
 	case X86_SUBARCH_INTEL_MID: