linux-kernel - Re: [patches] [PATCH] [28/34] i386: pte xchg optimization

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:	Wed, 02 May 2007 12:19:27 -0700
From:	Zachary Amsden <zach@...are.com>
To:	Andi Kleen <ak@...ell.com>
CC:	Jan Beulich <jbeulich@...ell.com>, linux-kernel@...r.kernel.org,
	patches@...-64.org
Subject: Re: [patches] [PATCH] [28/34] i386: pte xchg optimization

Andi Kleen wrote:
>> I always wondered why the xchg is necessary here at all. If the process of
>> tearing down a page table entry has started, other users of the mapped
>> linear address are broken anyway - why is it necessary to still monitor the
>> effect they may have on the A/D bits, unless this is a transient tear down?
>>
>> Checking for the uses of ptep_get_and_clear, I would judge that the use in
>> change_pte_range() may in fact need the xchg, but the uses in
>> vunmap_pte_range() and zap_pte_range() shouldn't.
>>     
>
> Yes I agree. Might be a nice speed up for exit to distingush the cases.
>   

That is what I did in this patch - but with care zap_pte_range can also 
be called in non-teardown cases when unmapping (when !fullmm) and user 
mappings could still be in effect on remote processors.

Zach
-
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/