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

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Message-ID: <20140111122723.GA11475@amt.cnet>
Date:	Sat, 11 Jan 2014 10:27:23 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Hu Yaohui <loki2441@...il.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

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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