linux-kernel - Re: [PATCH] intel-iommu: Synchronize gcmd value with global command register

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: <20130405110616.GB6858@8bytes.org>
Date:	Fri, 5 Apr 2013 13:06:16 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Takao Indoh <indou.takao@...fujitsu.com>,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	kexec@...ts.infradead.org
Subject: Re: [PATCH] intel-iommu: Synchronize gcmd value with global command
 register

On Wed, Apr 03, 2013 at 09:24:39AM +0100, David Woodhouse wrote:
> On Wed, 2013-04-03 at 16:11 +0900, Takao Indoh wrote:
> > Yeah, you are right. I forgot such a case.
> 
> If you disable translation and there's some device still doing DMA, it's
> going to scribble over random areas of memory. You really want to have
> translation enabled and all the page tables *cleared*, during kexec. I
> think it's fair to insist that the secondary kernel should use the IOMMU
> if the first one did.

Do we really need to insist on that? The IOMMU initialization on x86
happens after the kernel scanned and enumerated the PCI bus. While doing
this the kernel (at least it should) disables all devices it finds. So
when the IOMMU init code runs we should be safe from any in-flight DMA
and can either disable translation or re-initialize it for the kdump
kernel. Until then translation needs to stay enabled of course, so that
the old page-tables are still used and in-flight DMA doesn't corrupt
any data.

	Joerg

--
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/