linux-kernel - Re: [PART1 RFC v3 12/12] svm: Manage vcpu load/unload when enable AVIC

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Message-ID: <56FCE556.80306@amd.com>
Date:	Thu, 31 Mar 2016 15:52:38 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Radim Krčmář <rkrcmar@...hat.com>
CC:	<pbonzini@...hat.com>, <joro@...tes.org>, <bp@...en8.de>,
	<gleb@...nel.org>, <alex.williamson@...hat.com>,
	<kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<wei@...hat.com>, <sherry.hurwitz@....com>
Subject: Re: [PART1 RFC v3 12/12] svm: Manage vcpu load/unload when enable
 AVIC

Hi Radim,

On 03/19/2016 04:44 AM, Radim Krčmář wrote:
> 2016-03-18 01:09-0500, Suravee Suthikulpanit:
>> From: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
>> +
>> +		WRITE_ONCE(*entry, new_entry);
>
> This will translate to two writes in 32 bit mode and we need to write
> physical ID first to avoid spurious doorbells ...
> is the order guaranteed?

Hm.. not sure on that.

>> +	} else {
>> +		new_entry = READ_ONCE(*entry);
>> +		/**
>> +		 * This handles the case when vcpu is scheduled out
>> +		 * and has not yet not called blocking. We save the
>> +		 * AVIC running flag so that we can restore later.
>> +		 */
>
> is_running must be disabled in between ...blocking and ...unblocking,
> because we don't want to miss interrupts and block forever.
> I somehow don't get it from the comment. :)

Not sure if I understand your concern.  However, the is_running bit 
setting/clearing should be handled in the avic_set_running below. This 
part only handles othe case when the is_running bit still set when 
calling vcpu_put (and later on loading some other vcpus). This way, when 
we are re-loading this vcpu, we can restore the is_running bit accordingly.

Thanks,
Suravee