linux-kernel - Re: [PATCH 0/2] x86/mm: remove arch-specific PTE/PMD get-and-clear functions

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: <20120613140404.GH5979@phenom.dumpdata.com>
Date:	Wed, 13 Jun 2012 10:04:04 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	xen-devel@...ts.xensource.com, "H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] x86/mm: remove arch-specific PTE/PMD get-and-clear
 functions

On Wed, Jun 13, 2012 at 11:20:43AM +0100, David Vrabel wrote:
> This series removes the x86-specific implementation of
> ptep_get_and_clear() and pmdp_get_and_clear().
> 
> The principal reason for this is it allows Xen paravitualized guests
> to batch the PTE clears which is a significant performance
> optimization of munmap() and mremap() -- the number of entries into
> the hypervisor is reduced by about a factor of about 30 (60 in 32-bit
> guests) for munmap().
> 
> There may be minimal gains on native and KVM guests due to the removal
> of the locked xchg.

What about lguest?
> 
> Removal of arch-specific functions where generic ones are suitable
> seems to be a generally useful thing to me.
> 
> The full reasoning for why this is safe is included in the commit
> message of patch 1 but to summarize.  The atomic get-and-clear does
> not guarantee that the latest dirty/accessed bits are returned as TLB
> as there is a still a window after the get-and-clear and before the
> TLB flush that the bits may be updated on other processors.  So, user
> space applications accessing pages that are being unmapped or remapped
> already have unpredictable behaviour.
> 
> David
--
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/