linux-kernel - Re: [patch 1/9] Guest page hinting: unused / free pages.

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 linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <45083A50.8030708@watson.ibm.com>
Date:	Wed, 13 Sep 2006 13:05:20 -0400
From:	Hubertus Franke <frankeh@...son.ibm.com>
To:	schwidefsky@...ibm.com
CC:	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, akpm@...l.org,
	nickpiggin@...oo.com.au, rhim@...gatech.edu
Subject: Re: [patch 1/9] Guest page hinting: unused / free pages.

Martin Schwidefsky wrote:
> On Wed, 2006-09-13 at 10:45 -0400, Rik van Riel wrote:
> 
>>>But another trouble you have not mentioned is what happens to pages
>>>with pending make-volatile that need to and/or have been made stable
>>>in the meantime. They too need to be removed from this pending list.
>>
>>At the time where you walk the set of pages (pagevec?) to make
>>volatile, you can check whether the page flags are still right.
> 
> 
> A make volatile can be done anytime as long as the page is in page
> cache. Before a page can be made stable the caller needs to make sure
> that one of the conditions that prevent a make volatile becomes true.
> So a page in the pending make-volatile array does not have to be removed
> because a make stable has been done. It only has to be removed if it
> gets freed.
> 
> 
>>A page that was set to be marked volatile with the hypervisor,
>>but later turned stable again would have that indicated in its
>>page flags, right?
> 
> 
> Several page flag bits and some other conditions like "has a mapping"
> and "reference count is map count + 1". Most of the checks that need to
> be done for make volatile are on page flags.
> 

Interesting..
But don't we have to do some locking on the page to avoid race conditions?
A page needs to be consistent between check through __page_discardable and
committing to the hypervisor. We could raise the PG_state_change flag for
that period.


-
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/