On Thu, May 24, 2018 at 08:27:04AM +1000, Benjamin Herrenschmidt wrote: > On Wed, 2018-05-23 at 21:50 +0300, Michael S. Tsirkin wrote: > > > I re-read that discussion and I'm still unclear on the > > original question, since I got several apparently > > conflicting answers. > > > > I asked: > > > > Why isn't setting VIRTIO_F_IOMMU_PLATFORM on the > > hypervisor side sufficient? > > I thought I had replied to this... > > There are a couple of reasons: > > - First qemu doesn't know that the guest will switch to "secure mode" > in advance. There is no difference between a normal and a secure > partition until the partition does the magic UV call to "enter secure > mode" and qemu doesn't see any of it. So who can set the flag here ? This seems weird to me. As a rule HV calls should go through qemu - or be allowed to go directly to KVM *by* qemu. We generally reserve the latter for hot path things. Since this isn't a hot path, having the call handled directly by the kernel seems wrong. Unless a "UV call" is something different I don't know about. > - Second, when using VIRTIO_F_IOMMU_PLATFORM, we also make qemu (or > vhost) go through the emulated MMIO for every access to the guest, > which adds additional overhead. > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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