On Mon, Nov 26, 2012 at 05:44:29AM +0000, Zhang, Yang Z wrote: > 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. No, but we can add function to entry_(64|32).S that despatch via idt_table and expose it. Avi's idea is worth to explore before going self IPI way. > 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 > -- Gleb. -- 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
