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

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Date:	Mon, 11 May 2009 09:04:28 -0400
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: [RFC PATCH 0/3] generic hypercall support

Arnd Bergmann wrote:
> On Saturday 09 May 2009, Benjamin Herrenschmidt wrote:
>   
>> This was shot down by a vast majority of people, with the outcome being
>> an agreement that for IORESOURCE_MEM, pci_iomap and friends must return
>> something that is strictly interchangeable with what ioremap would have
>> returned.
>>
>> That means that readl and writel must work on the output of pci_iomap()
>> and similar, but I don't see why __raw_writel would be excluded there, I
>> think it's in there too.
>>     
>
> One of the ideas was to change pci_iomap to return a special token
> in case of virtual devices that causes iowrite32() to do an hcall,
> and to just define writel() to do iowrite32().
>
> Unfortunately, there is no __raw_iowrite32(), although I guess we
> could add this generically if necessary.
>
>   
>> Direct dereference is illegal in all cases though.
>>     
>
> right.
>  
>   
>> The token returned by pci_iomap for other type of resources (IO for
>> example) is also only supported for use by iomap access functions
>> (ioreadXX/iowriteXX) , and IO ports cannot be passed directly to those
>> neither.
>>     
>
> That still leaves the option to let drivers pass the IORESOURCE_PVIO
> for its own resources under some conditions, meaning that we will
> only use hcalls for I/O on these drivers but not on others, as Chris
> explained earlier.
>   

Between this, and Avi's "nesting" point, this is the direction I am
leaning in right now.

-Greg



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