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Subject[rfc 3/4] x86: apic - introduce dummy apic operations
In case if apic was disabled by kernel option
or hardware limits we could use dummy operations
such as apic->write at moment.

Same time the patch fixes the missed EOI in
do_IRQ function (which has place if kernel
is compiled as X86-32 and interrupt without
handler happens where apic was not asked to
be disabled via kernel option).

Note that native_apic_write_dummy consists of
WARN_ON_ONCE to catch any unpredictable
writes on enabled APICs. Could be removed
after long time of testing.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
---
arch/x86/include/asm/apic.h | 3 ++-
arch/x86/kernel/apic/apic.c | 24 ++++++++++++++++++++++++
arch/x86/kernel/irq.c | 10 ++--------
3 files changed, 28 insertions(+), 9 deletions(-)
Index: linux-2.6.git/arch/x86/include/asm/apic.h
=====================================================================
--- linux-2.6.git.orig/arch/x86/include/asm/apic.h
+++ linux-2.6.git/arch/x86/include/asm/apic.h
@@ -212,6 +212,7 @@ static inline void ack_x2APIC_irq(void)
}
#endif

+extern void apic_disable(void);
extern int lapic_get_maxlvt(void);
extern void clear_local_APIC(void);
extern void connect_bsp_APIC(void);
@@ -252,7 +253,7 @@ static inline void lapic_shutdown(void)
#define local_apic_timer_c2_ok 1
static inline void init_apic_mappings(void) { }
static inline void disable_local_APIC(void) { }
-
+static inline void apic_disable(void) { }
#endif /* !CONFIG_X86_LOCAL_APIC */

#ifdef CONFIG_X86_64
Index: linux-2.6.git/arch/x86/kernel/apic/apic.c
=====================================================================
--- linux-2.6.git.orig/arch/x86/kernel/apic/apic.c
+++ linux-2.6.git/arch/x86/kernel/apic/apic.c
@@ -233,6 +233,24 @@ static int modern_apic(void)
return lapic_get_version() >= 0x14;
}

+/*
+ * bare function to substitute write operation
+ * and it's _that_ fast :)
+ */
+void native_apic_write_dummy(u32 reg, u32 v)
+{
+ WARN_ON_ONCE((cpu_has_apic || !disable_apic));
+}
+
+/*
+ * right after this call apic->write doesn't do anything
+ * note that there is no restore operation it works one way
+ */
+void apic_disable(void)
+{
+ apic->write = native_apic_write_dummy;
+}
+
void native_apic_wait_icr_idle(void)
{
while (apic_read(APIC_ICR) & APIC_ICR_BUSY)
@@ -1592,6 +1610,12 @@ void __init init_apic_mappings(void)
*/
if (boot_cpu_physical_apicid == -1U)
boot_cpu_physical_apicid = read_apic_id();
+
+ /* lets check if we may to NOP'ify apic operations */
+ if (!cpu_has_apic) {
+ pr_info("APIC: disable apic facility\n");
+ apic_disable();
+ }
}

/*
Index: linux-2.6.git/arch/x86/kernel/irq.c
=====================================================================
--- linux-2.6.git.orig/arch/x86/kernel/irq.c
+++ linux-2.6.git/arch/x86/kernel/irq.c
@@ -27,7 +27,6 @@ void ack_bad_irq(unsigned int irq)
if (printk_ratelimit())
pr_err("unexpected IRQ trap at vector %02x\n", irq);

-#ifdef CONFIG_X86_LOCAL_APIC
/*
* Currently unexpected vectors happen only on SMP and APIC.
* We _must_ ack these because every local APIC has only N
@@ -37,9 +36,7 @@ void ack_bad_irq(unsigned int irq)
* completely.
* But only ack when the APIC is enabled -AK
*/
- if (cpu_has_apic)
- ack_APIC_irq();
-#endif
+ ack_APIC_irq();
}

#define irq_stats(x) (&per_cpu(irq_stat, x))
@@ -224,10 +221,7 @@ unsigned int __irq_entry do_IRQ(struct p
irq = __get_cpu_var(vector_irq)[vector];

if (!handle_irq(irq, regs)) {
-#ifdef CONFIG_X86_64
- if (!disable_apic)
- ack_APIC_irq();
-#endif
+ ack_APIC_irq();

if (printk_ratelimit())
pr_emerg("%s: %d.%d No irq handler for vector (irq %d)\n",


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