x86: APIC: remove apic_write_around(); use alternatives

Use alternatives to select the workaround for the 11AP Pentium erratum
for the affected steppings on the fly rather than build time.  Remove the
X86_GOOD_APIC configuration option and replace all the calls to
apic_write_around() with plain apic_write(), protecting accesses to the
ESR as appropriate due to the 3AP Pentium erratum.  Remove
apic_read_around() and all its invocations altogether as not needed.
Remove apic_write_atomic() and all its implementing backends.  The use of
ASM_OUTPUT2() is not strictly needed for input constraints, but I have
used it for readability's sake.

I had the feeling no one else was brave enough to do it, so I went ahead
and here it is.  Verified by checking the generated assembly and tested
with both a 32-bit and a 64-bit configuration, also with the 11AP
"feature" forced on and verified with gdb on /proc/kcore to work as
expected (as an 11AP machines are quite hard to get hands on these days).
Some script complained about the use of "volatile", but apic_write() needs
it for the same reason and is effectively a replacement for writel(), so I
have disregarded it.

I am not sure what the policy wrt defconfig files is, they are generated
and there is risk of a conflict resulting from an unrelated change, so I
have left changes to them out.  The option will get removed from them at
the next run.

Some testing with machines other than mine will be needed to avoid some
stupid mistake, but despite its volume, the change is not really that
intrusive, so I am fairly confident that because it works for me, it will
everywhere.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 17 deletions

diff --git a/include/asm-x86/apic.h b/include/asm-x86/apic.h
index 4e2c1e517f0..ea866baccef 100644
--- a/include/asm-x86/apic.h
+++ b/include/asm-x86/apic.h
@@ -3,6 +3,8 @@
 
 #include <linux/pm.h>
 #include <linux/delay.h>
+
+#include <asm/alternative.h>
 #include <asm/fixmap.h>
 #include <asm/apicdef.h>
 #include <asm/processor.h>
@@ -48,7 +50,6 @@ extern int disable_apic;
 #include <asm/paravirt.h>
 #else
 #define apic_write native_apic_write
-#define apic_write_atomic native_apic_write_atomic
 #define apic_read native_apic_read
 #define setup_boot_clock setup_boot_APIC_clock
 #define setup_secondary_clock setup_secondary_APIC_clock
@@ -58,12 +59,11 @@ extern int is_vsmp_box(void);
 
 static inline void native_apic_write(unsigned long reg, u32 v)
 {
-	*((volatile u32 *)(APIC_BASE + reg)) = v;
-}
+	volatile u32 *addr = (volatile u32 *)(APIC_BASE + reg);
 
-static inline void native_apic_write_atomic(unsigned long reg, u32 v)
-{
-	(void)xchg((u32 *)(APIC_BASE + reg), v);
+	alternative_io("movl %0, %1", "xchgl %0, %1", X86_FEATURE_11AP,
+		       ASM_OUTPUT2("=r" (v), "=m" (*addr)),
+		       ASM_OUTPUT2("0" (v), "m" (*addr)));
 }
 
 static inline u32 native_apic_read(unsigned long reg)
@@ -75,16 +75,6 @@ extern void apic_wait_icr_idle(void);
 extern u32 safe_apic_wait_icr_idle(void);
 extern int get_physical_broadcast(void);
 
-#ifdef CONFIG_X86_GOOD_APIC
-# define FORCE_READ_AROUND_WRITE 0
-# define apic_read_around(x)
-# define apic_write_around(x, y) apic_write((x), (y))
-#else
-# define FORCE_READ_AROUND_WRITE 1
-# define apic_read_around(x) apic_read(x)
-# define apic_write_around(x, y) apic_write_atomic((x), (y))
-#endif
-
 static inline void ack_APIC_irq(void)
 {
 	/*
@@ -95,7 +85,7 @@ static inline void ack_APIC_irq(void)
 	 */
 
 	/* Docs say use 0 for future compatibility */
-	apic_write_around(APIC_EOI, 0);
+	apic_write(APIC_EOI, 0);
 }
 
 extern int lapic_get_maxlvt(void);