• Gleb Natapov's avatar
    x86/apic: Enable x2APIC without interrupt remapping under KVM · ce69a784
    Gleb Natapov authored
    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>
    ce69a784
apic.h 13.3 KB