linux-kernel - Re: [Xen-devel] Re: [PATCH 1 of 7] x86: add _PAGE

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

Date:	Tue, 09 Sep 2008 16:29:04 +0100
From:	Keir Fraser <keir.fraser@...citrix.com>
To:	Avi Kivity <avi@...ranet.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Andi Kleen <andi@...stfloor.org>,
	<linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] Re: [PATCH 1 of 7] x86: add _PAGE_IOMAP pte flag
 for IO mappings

On 9/9/08 15:56, "Avi Kivity" <avi@...ranet.com> wrote:

>> I'm not sure; I still don't really understand how _PAGE_SPECIAL gets
>> used, other than being user-mode mapping only.  But in principle,
>> _PAGE_IOMAP could be set on both kernel and user mappings (if you direct
>> map a device into a process address space), so I think they would
>> conflict then?
> 
> It's a "don't refcount me" flag, which is not sematically the same as
> I/O, but may be close enough.

That's basically what our _PAGE_IO flag (in our old Linux patchset) means.
We use it to cause pte_pfn() to return an invalid pfn and hence avoid
reference counting that way. Since kernel mappings are never reference
counted (I think?) perhaps we could use _PAGE_SPECIAL even if it is
restricted to use on user mappings.

 -- Keir


--
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/