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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.02.17 at 09:49, <chao.gao@xxxxxxxxx> wrote:
> 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.

Good point, I think we indeed want to retain the old behavior (but
in a not open coded fashion) for the cpu == smp_processor_id()
case.

Jan


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