linux-kernel - Re: [RFC PATCH 0/3] generic hypercall support

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Date:	Thu, 07 May 2009 14:16:59 -0400
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Gregory Haskins <ghaskins@...ell.com>,
	Chris Wright <chrisw@...s-sol.org>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: [RFC PATCH 0/3] generic hypercall support

Avi Kivity wrote:
> Gregory Haskins wrote:
>>> What do you think of my mmio hypercall?  That will speed up all mmio
>>> to be as fast as a hypercall, and then we can use ordinary mmio/pio
>>> writes to trigger things.
>>>
>>>     
>> I like it!
>>
>> Bigger question is what kind of work goes into making mmio a pv_op (or
>> is this already done)?
>>
>>   
>
> Looks like it isn't there.  But it isn't any different than set_pte -
> convert a write into a hypercall.
>
>

I guess technically mmio can just be a simple access of the page which
would be problematic to trap locally without a PF.  However it seems
that most mmio always passes through a ioread()/iowrite() call so this
is perhaps the hook point.  If we set the stake in the ground that mmios
that go through some other mechanism like PFs can just hit the "slow
path" are an acceptable casualty, I think we can make that work.

Thoughts?

-Greg

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