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

From: "Xuquan (Quan Xu)" <xuquan8@huawei.com>
To: Jan Beulich <JBeulich@suse.com>, Chao Gao <chao.gao@intel.com>,
	Kevin Tian <kevin.tian@intel.com>
Cc: "yang.zhang.wz@gmail.com" <yang.zhang.wz@gmail.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	"quan.xu0@gmail.com" <quan.xu0@gmail.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [PATCH] x86/apicv: enhance posted-interrupt processing
Date: Mon, 20 Feb 2017 11:25:29 +0000	[thread overview]
Message-ID: <E0A769A898ADB6449596C41F51EF62C6AE7393@SZXEMI506-MBX.china.huawei.com> (raw)
In-Reply-To: <58A733C3020000780013B652@prv-mh.provo.novell.com>

On February 18, 2017 12:33 AM, Jan Beulich wrote:
>>>> On 17.02.17 at 09:49, <chao.gao@intel.com> 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@huawei.com>
>>>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@huawei.com>
>>>---
>>> 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.
>

Chao, __iiuc__, your question may be from the comments of xen/arch/x86/hvm/vmx/vmx.c :: pi_notification_interrupt() ..
IF VT-d PI is enabled, 
   VCPU_KICK_SOFTIRQ bit is set by ' raise_softirq(VCPU_KICK_SOFTIRQ)', at the end of pi_notification_interrupt()..
Else 
  Is it possible for your case?

I hope Kevin could help us to check/correct it.

>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.
>
__iiuc__
for the cpu == smp_processor_id() case, the vCPUs (cpu = v->processor) pending to this cpu, are indeed not in guest-mode..

Quan

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