Re: [Xen-devel] [PATCH] x86/apicv: enhance posted-interrupt processing

[Chao Gao <chao.gao@xxxxxxxxx>]

On Fri, Feb 17, 2017 at 09:37:45AM +0000, Xuquan (Quan Xu) wrote:
>From a589074281cc22a30ed75a5bccba60e83d2312a6 Mon Sep 17 00:00:00 2001
>From: Quan Xu <xuquan8@xxxxxxxxxx>
>Date: Sat, 18 Feb 2017 09:27:37 +0800
>Subject: [PATCH] x86/apicv: enhance posted-interrupt processing
>
>If guest is already in non-root mode, an posted interrupt will
>be directly delivered to guest (leaving softirq being set w/o
>actually incurring a VM-Exit - breaking desired softirq behavior).
>Then further posted interrupts will skip the IPI, stay in PIR and
>not noted until another VM-Exit happens.
>
>Remove the softirq set. Actually since it's an optimization for
>less IPIs, check softirq_pending(cpu) directly instead of sticking
>to one bit only.
>
>Signed-off-by: Quan Xu <xuquan8@xxxxxxxxxx>
>---
> xen/arch/x86/hvm/vmx/vmx.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
>diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>index 61925cf..3887c32 100644
>--- a/xen/arch/x86/hvm/vmx/vmx.c
>+++ b/xen/arch/x86/hvm/vmx/vmx.c
>@@ -1846,8 +1846,7 @@ static void __vmx_deliver_posted_interrupt(struct vcpu 
>*v)
>     {
>         unsigned int cpu = v->processor;
>
>-        if ( !test_and_set_bit(VCPU_KICK_SOFTIRQ, &softirq_pending(cpu))
>-             && (cpu != smp_processor_id()) )
>+        if ( !softirq_pending(cpu) && (cpu != smp_processor_id()) )
HI, Quan.
Is there a situation that we need set VCPU_KICK_SOFTIRQ. For example,
after vmx_intr_assist(), a interrupt happened and its handler called this
function to deliver interrupt to current vcpu. In that case, the interrupt
would not be injected to guest before this VM-entry for we don't generate a
softirq and don't send a self-IPI to current vcpu.

Thanks,
Chao
>             send_IPI_mask(cpumask_of(cpu), posted_intr_vector);
>     }
> }
>--
>1.8.3.1



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