On Mon, Jun 29, 2009 at 11:45 PM, Gleb Natapov<gleb@xxxxxxxxxx> wrote:
> 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).
>
> Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 8c7c042..351d55a 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -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;
>
> @@ -1363,52 +1364,75 @@ 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_info("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 x2apic is enabled by BIOS even
> + * when running in kvm since this indicates present
> + * of APIC ID > 255 */
> + if (x2apic_preenabled || !kvm_para_available())
> + goto nox2apic;
> + else
> + /* without IR all CPUs can be addressed by IOAPIC/MSI
> + * only in physical mode */
> + x2apic_phys = 1;
> + }
how about kexec second kernel in KVM ?
x2apic_preenabled will be set in second kernel.
YH
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