linux-kernel - Re: [PATCH] kvm: x86: Fix debug typo error in lapic

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Message-ID: <CAHqbYQu=UKmHUadT+LHFNaN93uNTfjcs3f=QNJ3+9mL-QzAGCA@mail.gmail.com>
Date:	Sun, 12 Jan 2014 14:40:21 -0500
From:	Hu Yaohui <loki2441@...il.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	kvm <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chen Fan <chen.fan.fnst@...fujitsu.com>, gleb@...hat.com,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH] kvm: x86: Fix debug typo error in lapic

Thank you Marcelo!
I really appreciate your explanation.

On Sat, Jan 11, 2014 at 7:27 AM, Marcelo Tosatti <mtosatti@...hat.com> wrote:
> On Thu, Jan 09, 2014 at 03:08:25PM -0500, Hu Yaohui wrote:
>> Hi Marcelo,
>> Thanks for your replying!
>> I hope you have a good day! I am sorry that it's not that obvious to
>> me after I checked that function.
>> If the remote vcpu is not in the same pcpu as the sender which calls
>> kvm_vpcu_kick.
>> Before the remote vcpu received the Host-IPI, it could be in guest
>> mode which could possibly access the stale tlb entry that have been
>> modifed by the sender.
>>
>> For smp_call_function_wait, the wait parameter will only let the
>> sender side wait until the function has been executed on all the
>> target cpus, then return.
>> For TLB Flush IPI, the sender has already invalidate one tlb entry,
>> the received side should get the IPI ASAP to invalidate the specified
>> tlb before it's accessed, or there should have some mechanisms to
>> enusre that even the stale tlb entry is accessed, it's still ok. I am
>> not sure what's the situation here after I reviewed all the source
>> codes.
>
> The sender only considers the TLB entry (or entries) flushed when
> smp_call_function_wait finishes, that is when the receiver cpu acknowledges
> it has flushed its TLB.
>
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