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Re: [PATCH v5 07/18] s390x: protvirt: Inhibit balloon when switching to
Michael S. Tsirkin
Re: [PATCH v5 07/18] s390x: protvirt: Inhibit balloon when switching to protected mode
Thu, 19 Mar 2020 13:45:55 -0400
On Thu, Mar 19, 2020 at 02:54:11PM +0100, David Hildenbrand wrote:
> Why does the balloon driver not support VIRTIO_F_IOMMU_PLATFORM? It is
> absolutely not clear to me. The introducing commit mentioned that it
> "bypasses DMA". I fail to see that.
Well sure one can put the balloon behind an IOMMU. If will shuffle PFN
lists through a shared page. Problem is, you can't run an untrusted
driver with it since if you do it can corrupt guest memory.
And VIRTIO_F_IOMMU_PLATFORM so far meant that you can run
a userspace driver.
Maybe we need a separate feature bit for this kind of thing where you
assume the driver is trusted? Such a bit - unlike
VIRTIO_F_IOMMU_PLATFORM - would allow legacy guests ...