Re: [tip:x86/apic] x86: read apic ID in the !acpi_lapic case

Yinghai Lu
2009-05-11T20:15:43Z

Ingo Molnar wrote:

> Needs a delta patch against -tip - i got this stuff stable today but
> i dont want to replace patches as it has a problematic track record
> already.
>

diff to current tip/master

[PATCH] x86: add native_apic_read_dummy -v2

when apic is not used ( not there, or disable_apic ), try to install
dummy read too.

could save 4k in that case.

v2: update to after Cyrill's patch

[ Impact: fix bug when try to dump APIC reg ]

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>

---
arch/x86/include/asm/smp.h | 2 -
arch/x86/kernel/apic/apic.c | 46 +++++++++++++++++++----------------------
arch/x86/kernel/apic/io_apic.c | 5 ++++
3 files changed, 28 insertions(+), 25 deletions(-)

Index: linux-2.6/arch/x86/kernel/apic/apic.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/apic/apic.c
+++ linux-2.6/arch/x86/kernel/apic/apic.c
@@ -243,17 +243,24 @@ static int modern_apic(void)
* bare function to substitute write operation
* and it's _that_ fast :)
*/
-void native_apic_write_dummy(u32 reg, u32 v)
+static void native_apic_write_dummy(u32 reg, u32 v)
{
WARN_ON_ONCE((cpu_has_apic || !disable_apic));
}

+static u32 native_apic_read_dummy(u32 reg)
+{
+ WARN_ON_ONCE((cpu_has_apic || !disable_apic));
+ return 0;
+}
+
/*
- * right after this call apic->write doesn't do anything
+ * right after this call apic->write/read doesn't do anything
* note that there is no restore operation it works one way
*/
void apic_disable(void)
{
+ apic->read = native_apic_read_dummy;
apic->write = native_apic_write_dummy;
}

@@ -1580,32 +1587,23 @@ void __init init_apic_mappings(void)
return;
}

- /*
- * If no local APIC can be found then set up a fake all
- * zeroes page to simulate the local APIC and another
- * one for the IO-APIC.
- */
+ /* If no local APIC can be found return early */
if (!smp_found_config && detect_init_APIC()) {
- apic_phys = (unsigned long) alloc_bootmem_pages(PAGE_SIZE);
- apic_phys = __pa(apic_phys);
- } else
+ /* lets NOP'ify apic operations */
+ pr_info("APIC: disable apic facility\n");
+ apic_disable();
+ } else {
apic_phys = mp_lapic_addr;

- /*
- * acpi lapic path already maps that address in
- * acpi_register_lapic_address()
- */
- if (!acpi_lapic)
- set_fixmap_nocache(FIX_APIC_BASE, apic_phys);
-
- apic_printk(APIC_VERBOSE, "mapped APIC to %08lx (%08lx)\n",
- APIC_BASE, apic_phys);
+ /*
+ * acpi lapic path already maps that address in
+ * acpi_register_lapic_address()
+ */
+ if (!acpi_lapic)
+ set_fixmap_nocache(FIX_APIC_BASE, apic_phys);

- /* lets check if we may NOP'ify apic operations */
- if (!cpu_has_apic) {
- pr_info("APIC: disable apic facility\n");
- apic_disable();
- return;
+ apic_printk(APIC_VERBOSE, "mapped APIC to %08lx (%08lx)\n",
+ APIC_BASE, apic_phys);
}

/*
Index: linux-2.6/arch/x86/kernel/apic/io_apic.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/apic/io_apic.c
+++ linux-2.6/arch/x86/kernel/apic/io_apic.c
@@ -1859,6 +1859,11 @@ __apicdebuginit(void) print_PIC(void)
__apicdebuginit(int) print_all_ICs(void)
{
print_PIC();
+
+ /* don't print out if apic is not there */
+ if (!cpu_has_apic || disable_apic)
+ return 0;
+
print_all_local_APICs();
print_IO_APIC();

Index: linux-2.6/arch/x86/include/asm/smp.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/smp.h
+++ linux-2.6/arch/x86/include/asm/smp.h
@@ -180,7 +180,7 @@ extern int safe_smp_processor_id(void);
static inline int logical_smp_processor_id(void)
{
/* we don't want to mark this access volatile - bad code generation */
- return GET_APIC_LOGICAL_ID(*(u32 *)(APIC_BASE + APIC_LDR));
+ return GET_APIC_LOGICAL_ID(apic_read(APIC_LDR));
}

#endif