linux-kernel - Re: [PATCH v4 0/6] virtio core DMA API conversion

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: <5640914D.6070401@redhat.com>
Date:	Mon, 9 Nov 2015 13:27:57 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	Andy Lutomirski <luto@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	sparclinux@...r.kernel.org, Joerg Roedel <jroedel@...e.de>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@....de>, benh@...nel.crashing.org,
	KVM <kvm@...r.kernel.org>, dwmw2@...radead.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-s390 <linux-s390@...r.kernel.org>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v4 0/6] virtio core DMA API conversion



On 09/11/2015 13:15, Michael S. Tsirkin wrote:
> Well that's not exactly true. I think we would like to make
> it possible to put virtio devices behind an IOMMU on x86,
> but if this means existing guests break, then many people won't be able
> to use this option: having to find out which kernel version your guest
> is running is a significant burden.
> 
> So on the host side, we need to detect guests that
> don't program the IOMMU and make QEMU ignore it.
> I think we need to figure out a way to do this
> before we commit to the guest change.

What is the usecase for putting virtio devices behind an IOMMU, apart from:

1) "because you can"

2) using VFIO within the guest

?  Case 1 can be ignored, and in case 2 the guest will do the right thing.

> Additionally, IOMMU overhead is very high when running within the VM.
> So for uses such as VFIO, we'd like a way to make something like
> iommu-pt the default.

That's not something that the kernel cares about.  It's just a
configuration issue.

Paolo
--
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/