From: Rusty Russell <rusty@rustcorp.com.au>
To: Will Deacon <will.deacon@arm.com>
Cc: "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Sasha Levin <levinsasha928@gmail.com>,
Marc Zyngier <Marc.Zyngier@arm.com>,
lf-virt <virtualization@lists.linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Eric Van Hensbergen <ericvh@gmail.com>
Subject: Re: [PATCH] virtio: 9p: correctly pass physical address to userspace for high pages
Date: Fri, 19 Oct 2012 10:09:51 +1030 [thread overview]
Message-ID: <87wqynpcxk.fsf@rustcorp.com.au> (raw)
In-Reply-To: <20121018094247.GA17296@mudshark.cambridge.arm.com>
Will Deacon <will.deacon@arm.com> writes:
> On Thu, Oct 18, 2012 at 03:19:06AM +0100, Rusty Russell wrote:
>> We do have an alternate solution: masking out __GFP_HIGHMEM from the
>> kmalloc of desc. If it fails, we will fall back to laying out the
>> virtio request directly inside the ring; if it doesn't fit, we'll wait
>> for the device to consume more buffers.
>
> Hmm, that will probably work for the vring but the zero-copy code for 9p may
> just give us an address from userspace if I'm understanding it correctly. In
> that case, we really have to do the translation as below (which is actually
> much cleaner because everything is page-aligned).
>
>> > @@ -325,7 +326,7 @@ static int p9_get_mapped_pages(struct virtio_chan *chan,
>> > int count = nr_pages;
>> > while (nr_pages) {
>> > s = rest_of_page(data);
>> > - pages[index++] = virt_to_page(data);
>> > + pages[index++] = kmap_to_page(data);
>> > data += s;
>> > nr_pages--;
>> > }
>
> So what do you reckon? How about I leave this hunk as a separate patch and
> have a play masking out __GFP_HIGHMEM for the vring descriptor?
Yes, I think so. A scathing comment would be nice, too...
Thanks,
Rusty.
prev parent reply other threads:[~2012-10-19 0:39 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-17 10:14 [PATCH] virtio: 9p: correctly pass physical address to userspace for high pages Will Deacon
2012-10-17 16:05 ` Sasha Levin
2012-10-17 16:17 ` Will Deacon
2012-10-18 2:19 ` Rusty Russell
2012-10-18 9:42 ` Will Deacon
2012-10-18 23:39 ` Rusty Russell [this message]
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