[Xen-devel] [PATCH v6 06/16] x86/init: use a platform legacy quirk for ebda

["Luis R. Rodriguez" <mcgrof@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 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 8bb8c1a4615a..89d9d57e145d 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 992f442ca155..afe65dffee80 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 021a5f973ce3..01b159781d96 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:
-- 
2.7.2


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