Avi Kivity wrote on 2012-11-25: > On 11/25/2012 03:03 PM, Gleb Natapov wrote: >> On Sun, Nov 25, 2012 at 02:55:26PM +0200, Avi Kivity wrote: >>> On 11/22/2012 05:22 PM, Gleb Natapov wrote: >>>> On Wed, Nov 21, 2012 at 04:09:38PM +0800, Yang Zhang wrote: >>>>> Ack interrupt on vmexit is required by Posted Interrupt. With it, >>>>> when external interrupt caused vmexit, the cpu will acknowledge the >>>>> interrupt controller and save the interrupt's vector in vmcs. >>>>> >>>>> There are several approaches to enable it. This patch uses a simply >>>>> way: re-generate an interrupt via self ipi. >>>>> >>>>> >>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>>>> index 7949d21..f6ef090 100644 >>>>> --- a/arch/x86/kvm/vmx.c >>>>> +++ b/arch/x86/kvm/vmx.c >>>>> @@ -2525,7 +2525,8 @@ static __init int setup_vmcs_config(struct > vmcs_config *vmcs_conf) >>>>> #ifdef CONFIG_X86_64 >>>>> min |= VM_EXIT_HOST_ADDR_SPACE_SIZE; >>>>> #endif >>>>> - opt = VM_EXIT_SAVE_IA32_PAT | VM_EXIT_LOAD_IA32_PAT; >>>>> + opt = VM_EXIT_SAVE_IA32_PAT | VM_EXIT_LOAD_IA32_PAT | >>>>> + VM_EXIT_ACK_INTR_ON_EXIT; >>>> Always? Do it only if posted interrupts are actually available >>>> and going to be used. >>> >>> Why not always? Better to have a single code path for host interrupts >>> (and as Yang notes, the new path is faster as well). >>> >> Is it? The current path is: >> >> vm exit -> KVM vmexit handler(interrupt disabled) -> KVM re-enable >> interrupt -> cpu ack the interrupt and interrupt deliver through the >> host IDT. >> >> The proposed path is: >> >> CPU acks interrupt -> vm exit -> KVM vmexit handler(interrupt disabled) >> -> eoi -> self IPI -> KVM re-enable interrupt -> cpu ack the interrupt >> and interrupt deliver through the host IDT. >> >> Am I missing something? > > Yes, you're missing the part where I didn't write that the new path > should avoid the IDT and dispatch the interrupt directly, by emulating > an interrupt frame directly. Can be as simple as pushf; push cs; call > interrupt_table[vector * 8]. Of course we need to verify that no > interrupt uses the IST or a task gate. How can we call interrupt table directly? I don't think we can expose the idt_table to a module. Anyway, to simply the implementation, I will follow gleb's suggestion: only enable "ack intr on exit" when PI is enabled and self ipi should be enough. Any comments? Best regards, Yang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
