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@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: andrew.cooper3@citrix.com
Cc: andriy.shevchenko@linux.intel.com
Cc: bigeasy@linutronix.de
Cc: boris.ostrovsky@oracle.com
Cc: david.vrabel@citrix.com
Cc: ffainelli@freebox.fr
Cc: george.dunlap@citrix.com
Cc: glin@suse.com
Cc: jgross@suse.com
Cc: jlee@suse.com
Cc: josh@joshtriplett.org
Cc: julien.grall@linaro.org
Cc: konrad.wilk@oracle.com
Cc: kozerkov@parallels.com
Cc: lenb@kernel.org
Cc: lguest@lists.ozlabs.org
Cc: linux-acpi@vger.kernel.org
Cc: lv.zheng@intel.com
Cc: matt@codeblueprint.co.uk
Cc: mbizon@freebox.fr
Cc: rjw@rjwysocki.net
Cc: robert.moore@intel.com
Cc: rusty@rustcorp.com.au
Cc: tiwai@suse.de
Cc: toshi.kani@hp.com
Cc: xen-devel@lists.xensource.com
Link: http://lkml.kernel.org/r/1460592286-300-7-git-send-email-mcgrof@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 8bb8c1a4615a45aef388c2b5548f6efb725ff076..89d9d57e145dfe8902542c5f8c02f6e97b1bd6c6 100644 (file)
--- 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 992f442ca15511d1d0c2c5773cd26e31b9d353c3..afe65dffee80b80bda7dc1f69072fc23d21472b3 100644 (file)
--- 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 021a5f973ce32774d7c4b0ef9dea2091dc93e54f..01b159781d96c2781517c25d3594e38e7d87c87f 100644 (file)
--- 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: