lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Tue, 6 Oct 2015 10:58:02 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	Roger Pau Monné <roger.pau@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<ian.campbell@...rix.com>, <stefano.stabellini@...citrix.com>,
	<linux-kernel@...r.kernel.org>,
	David Vrabel <david.vrabel@...rix.com>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH 2/2] block/xen-blkfront: Handle non-indirect
 grant with 64KB pages

Hi Roger,

On 06/10/2015 10:39, Roger Pau Monné wrote:
> El 05/10/15 a les 19.05, Julien Grall ha escrit:
>> On 05/10/15 17:01, Roger Pau Monné wrote:
>>> El 11/09/15 a les 21.32, Julien Grall ha escrit:
>>>>   		ring_req->u.rw.nr_segments = num_grant;
>>>> +		if (unlikely(require_extra_req)) {
>>>> +			id2 = blkif_ring_get_request(info, req, &ring_req2);
>>>
>>> How can you guarantee that there's always going to be another free
>>> request? AFAICT blkif_queue_rq checks for RING_FULL, but you don't
>>> actually know if there's only one slot or more than one available.
>>
>> Because the depth of the queue is divided by 2 when the extra request is
>> used (see xlvbd_init_blk_queue).

I just noticed that I didn't mention this restriction in the commit 
message. I will do it in the next revision.

> I see, that's quite restrictive but I guess it's better than introducing
> a new ring macro in order to figure out if there are at least two free
> slots.

I actually didn't think about your suggestion. I choose to divide by two 
based on the assumption that the block framework will always try to send 
a request with the maximum data possible.

I don't know if this assumption is correct as I'm not fully aware how 
the block framework is working.

If it's valid, in the case of 64KB guest, the maximum size of a request 
would be 64KB when indirect segment is not supported. So we would end up 
with a lot of 64KB request which will require 2 ring request.

Regards,

-- 
Julien Grall
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists