Il 03/09/2014 10:05, Benjamin Herrenschmidt ha scritto: > On Wed, 2014-09-03 at 09:47 +0200, Paolo Bonzini wrote: >> >> IOMMU support for x86 is going to go in this week. > > But won't that break virtio on x86 ? Or will virtio continue bypassing > it ? IE, the guest side virtio doesn't expect an IOMMU and doesn't call > the dma mappings ops. > >> However, it is and likely will remain niche enough that I don't really >> care about performance loss from IOMMU support. If you enable it, you >> want it. >> >> So from the QEMU point of view we can simply add the direct-ram-access >> property, and have the pseries machine turn it on by default (while >> other machines can leave it off by default---they have no IOMMU and >> thus no performance cost). > > Well, it's only for virtio and should be on by default on x86 as well if > an iommu is installed no ? Yes, only for virtio---but for x86 I think it should be off by default, even if that means virtio+IOMMU requires a new kernel. Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
