From ce69a784504222c3ab6f1b3c357d09ec5772127a Mon Sep 17 00:00:00 2001 From: Gleb Natapov Date: Mon, 20 Jul 2009 15:24:17 +0300 Subject: 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: Gleb Natapov Acked-by: Suresh Siddha Cc: Sheng Yang Cc: "avi@redhat.com" LKML-Reference: <20090720122417.GR5638@redhat.com> Signed-off-by: Ingo Molnar --- arch/x86/kernel/apic/probe_64.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'arch/x86/kernel/apic/probe_64.c') diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c index bc3e880f9b82..f3b1037076e4 100644 --- a/arch/x86/kernel/apic/probe_64.c +++ b/arch/x86/kernel/apic/probe_64.c @@ -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 -- cgit v1.2.3