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Commit ce69a784 authored by Gleb Natapov's avatar Gleb Natapov Committed by Ingo Molnar
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x86/apic: Enable x2APIC without interrupt remapping under KVM 



KVM would like to provide x2APIC interface to a guest without emulating
interrupt remapping device. The reason KVM prefers guest to use x2APIC
is that x2APIC interface is better virtualizable and provides better
performance than mmio xAPIC interface:

 - msr exits are faster than mmio (no page table walk, emulation)
 - no need to read back ICR to look at the busy bit
 - one 64 bit ICR write instead of two 32 bit writes
 - shared code with the Hyper-V paravirt interface

Included patch changes x2APIC enabling logic to enable it even if IR
initialization failed, but kernel runs under KVM and no apic id is
greater than 255 (if there is one spec requires BIOS to move to x2apic
mode before starting an OS).

-v2: fix build
-v3: fix bug causing compiler warning

Signed-off-by: default avatarGleb Natapov <gleb@redhat.com>
Acked-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Cc: Sheng Yang <sheng@linux.intel.com>
Cc: "avi@redhat.com" <avi@redhat.com>
LKML-Reference: <20090720122417.GR5638@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 9910887a

arch/x86/include/asm/apic.h

+7 −0
Original line number Diff line number Diff line
@@ -183,6 +183,10 @@ static inline int x2apic_enabled(void) 
}



#define x2apic_supported()	(cpu_has_x2apic)

static inline void x2apic_force_phys(void)

{

	x2apic_phys = 1;

}

#else

static inline void check_x2apic(void)

{
@@ -194,6 +198,9 @@ static inline int x2apic_enabled(void) 
{

	return 0;

}

static inline void x2apic_force_phys(void)

{

}



#define	x2apic_preenabled 0

#define	x2apic_supported()	0

arch/x86/kernel/apic/apic.c

+46 −37
Original line number Diff line number Diff line
@@ -49,6 +49,7 @@ 
#include <asm/mtrr.h>

#include <asm/smp.h>

#include <asm/mce.h>

#include <asm/kvm_para.h>



unsigned int num_processors;
@@ -1361,52 +1362,76 @@ void enable_x2apic(void) 
}

#endif /* CONFIG_X86_X2APIC */



void __init enable_IR_x2apic(void)

int __init enable_IR(void)

{

#ifdef CONFIG_INTR_REMAP

	int ret;

	unsigned long flags;

	struct IO_APIC_route_entry **ioapic_entries = NULL;



	ret = dmar_table_init();

	if (ret) {

		pr_debug("dmar_table_init() failed with %d:\n", ret);

		goto ir_failed;

		return 0;

	}



	if (!intr_remapping_supported()) {

		pr_debug("intr-remapping not supported\n");

		goto ir_failed;

		return 0;

	}





	if (!x2apic_preenabled && skip_ioapic_setup) {

		pr_info("Skipped enabling intr-remap because of skipping "

			"io-apic setup\n");

		return;

		return 0;

	}



	if (enable_intr_remapping(x2apic_supported()))

		return 0;



	pr_info("Enabled Interrupt-remapping\n");



	return 1;



#endif

	return 0;

}



void __init enable_IR_x2apic(void)

{

	unsigned long flags;

	struct IO_APIC_route_entry **ioapic_entries = NULL;

	int ret, x2apic_enabled = 0;



	ioapic_entries = alloc_ioapic_entries();

	if (!ioapic_entries) {

		pr_info("Allocate ioapic_entries failed: %d\n", ret);

		goto end;

		pr_err("Allocate ioapic_entries failed\n");

		goto out;

	}



	ret = save_IO_APIC_setup(ioapic_entries);

	if (ret) {

		pr_info("Saving IO-APIC state failed: %d\n", ret);

		goto end;

		goto out;

	}



	local_irq_save(flags);

	mask_IO_APIC_setup(ioapic_entries);

	mask_8259A();

	mask_IO_APIC_setup(ioapic_entries);



	ret = enable_intr_remapping(x2apic_supported());

	if (ret)

		goto end_restore;

	ret = enable_IR();

	if (!ret) {

		/* IR is required if there is APIC ID > 255 even when running

		 * under KVM

		 */

		if (max_physical_apicid > 255 || !kvm_para_available())

			goto nox2apic;

		/*

		 * without IR all CPUs can be addressed by IOAPIC/MSI

		 * only in physical mode

		 */

		x2apic_force_phys();

	}



	pr_info("Enabled Interrupt-remapping\n");

	x2apic_enabled = 1;



	if (x2apic_supported() && !x2apic_mode) {

		x2apic_mode = 1;
@@ -1414,41 +1439,25 @@ void __init enable_IR_x2apic(void) 
		pr_info("Enabled x2apic\n");

	}



end_restore:

	if (ret)

		/*

		 * IR enabling failed

		 */

nox2apic:

	if (!ret) /* IR enabling failed */

		restore_IO_APIC_setup(ioapic_entries);



	unmask_8259A();

	local_irq_restore(flags);



end:

out:

	if (ioapic_entries)

		free_ioapic_entries(ioapic_entries);



	if (!ret)

	if (x2apic_enabled)

		return;



ir_failed:

	if (x2apic_preenabled)

		panic("x2apic enabled by bios. But IR enabling failed");

		panic("x2apic: enabled by BIOS but kernel init failed.");

	else if (cpu_has_x2apic)

		pr_info("Not enabling x2apic,Intr-remapping\n");

#else

	if (!cpu_has_x2apic)

		return;



	if (x2apic_preenabled)

		panic("x2apic enabled prior OS handover,"

		      " enable CONFIG_X86_X2APIC, CONFIG_INTR_REMAP");

#endif



	return;

		pr_info("Not enabling x2apic, Intr-remapping init failed.\n");

}





#ifdef CONFIG_X86_64

/*

 * Detect and enable local APICs on non-SMP boards.

arch/x86/kernel/apic/probe_64.c

+3 −3
Original line number Diff line number Diff line
@@ -50,11 +50,11 @@ static struct apic *apic_probe[] __initdata = { 
void __init default_setup_apic_routing(void)

{

#ifdef CONFIG_X86_X2APIC

	if (x2apic_mode && (apic != &apic_x2apic_phys &&

	if (x2apic_mode

#ifdef CONFIG_X86_UV

		       apic != &apic_x2apic_uv_x &&

		       && apic != &apic_x2apic_uv_x

#endif

		       apic != &apic_x2apic_cluster)) {

		       ) {

		if (x2apic_phys)

			apic = &apic_x2apic_phys;

		else