linux-kernel - Re: lmbench lat_mmap slowdown with CONFIG

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]

Message-Id: <1232664907.16317.182.camel@bodhitayantram.eng.vmware.com>
Date:	Thu, 22 Jan 2009 14:55:07 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Nick Piggin <npiggin@...e.de>, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"jeremy@...source.com" <jeremy@...source.com>,
	"chrisw@...s-sol.org" <chrisw@...s-sol.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT

On Thu, 2009-01-22 at 14:44 -0800, Jeremy Fitzhardinge wrote:

> I did have some patches to do that at one point.  If you set pgd_val = 
> paravirt_nop, then the patching machinery will completely nop out the 
> call site.  The problem is that it depends on the calling convention 
> using the same regs for the first arg and return - true for 32-bit, but 
> not 64.  We could fix that with identity functions which the patcher 
> recognizes and can replace with either pure nops or inline appropriate 
> register moves.

What about removing the identity functions entirely.  They are useless,
really.  All that is needed is a patch site filled with nops for Xen to
overwrite, just stuffing the value into the proper registers.  For
64-bit, it can be a simple mov to satisfy the constraints.

> Also, I just posted patches to get rid of all pvops calls when fetching 
> or setting flags in a pte, which I hope will help.

Sounds like it will help.

--
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/