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

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Date:	Thu, 07 May 2009 15:29:01 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Gregory Haskins <ghaskins@...ell.com>
CC:	Chris Wright <chrisw@...s-sol.org>,
	Gregory Haskins <gregory.haskins@...il.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] generic hypercall support

Gregory Haskins wrote:
> Chris Wright wrote:
>   
>> * Gregory Haskins (ghaskins@...ell.com) wrote:
>>   
>>     
>>> Chris Wright wrote:
>>>     
>>>       
>>>> But a free-form hypercall(unsigned long nr, unsigned long *args, size_t count)
>>>> means hypercall number and arg list must be the same in order for code
>>>> to call hypercall() in a hypervisor agnostic way.
>>>>       
>>>>         
>>> Yes, and that is exactly the intention.  I think its perhaps the point
>>> you are missing.
>>>     
>>>       
>> Yes, I was reading this as purely any hypercall, but it seems a bit
>> more like:
>>  pv_io_ops->iomap()
>>  pv_io_ops->ioread()
>>  pv_io_ops->iowrite()
>>   
>>     
>
> Right.
>   

Hmm, reminds me of something I thought of a while back.

We could implement an 'mmio hypercall' that does mmio reads/writes via a 
hypercall instead of an mmio operation.  That will speed up mmio for 
emulated devices (say, e1000).  It's easy to hook into Linux 
(readl/writel), is pci-friendly, non-x86 friendly, etc.

It also makes the device work when hypercall support is not available 
(qemu/tcg); you simply fall back on mmio.

-- 
error compiling committee.c: too many arguments to function

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