[PATCH v5 06/14] x86/init: use a platform legacy quirk for ebda

Luis R. Rodriguez
2016-04-08T23:41:03Z

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>
---
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