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

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Message-ID: <20090507202506.GG3036@sequoia.sous-sol.org>
Date:	Thu, 7 May 2009 13:25:06 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Gregory Haskins <gregory.haskins@...il.com>
Cc:	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

* Gregory Haskins (gregory.haskins@...il.com) wrote:
> What I am not clear on is how you would know to flag the address to
> begin with.

That's why I mentioned pv_io_ops->iomap() earlier.  Something I'd expect
would get called on IORESOURCE_PVIO type.  This isn't really transparent
though (only virtio devices basically), kind of like you're saying below.

> Here's a thought: "PV" drivers can flag the IO (e.g. virtio-pci knows it
> would never be a real device).  This means we route any io requests from
> virtio-pci though pv_io_ops->mmio(), but not unflagged addresses.  This
> is not as slick as boosting *everyones* mmio speed as Avi's original
> idea would have, but it is perhaps a good tradeoff between the entirely
> new namespace created by my original dynhc() proposal and leaving them
> all PF based.
>
> This way, its just like using my dynhc() proposal except the mmio-addr
> is the substitute address-token (instead of the dynhc-vector). 
> Additionally, if you do not PV the kernel the IO_COND/pv_io_op is
> ignored and it just slow-paths through the PF as it does today.  Dynhc()
> would be dependent  on pv_ops.
> 
> Thoughts?
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