On Wed, 2019-12-18 at 15:53 +1100, Alexey Kardashevskiy wrote: > H_STUFF_TCE is always called with 0. Well, may be some AIX somewhere > calls it with a value other than zero, and I probably saw some other > value somewhere but in QEMU/KVM case it is 0 so you effectively disable > in-kernel acceleration of H_STUFF_TCE which is > undesirable. > Thanks for the feedback! > For now we should disable in-kernel H_STUFF_TCE/... handlers in QEMU > just like we do for VFIO for older host kernels: > > https://git.qemu.org/?p=qemu.git;a=blob;f=hw/ppc/spapr_iommu.c;h=3d3bcc86496a5277d62f7855fbb09c013c015f27;hb=HEAD#l208 I am still reading into this temporary solution, I could still not understand how it works. > I am not sure what a proper solution would be, something like an eventfd > and KVM's kvmppc_h_stuff_tce() signaling vhost that the latter needs to > invalidate iotlbs. Or we can just say that we do not allow KVM > acceleration if there is vhost+iommu on the same liobn (== vPHB, pretty > much). Thanks, I am not used to eventfd, but i agree it's a valid solution to talk to QEMU and then use it to send a message via /dev/vhost. KVM -> QEMU -> vhost But I can't get my mind out of another solution: doing it in kernelspace. I am not sure how that would work, though. If I could understand correctly, there is a vhost IOTLB per vhost_dev, and H_STUFF_TCE is not called in 64-bit DMA case (for tce_value == 0 case, at least), which makes sense, given it doesn't need to invalidate entries on IOTLB. So, we would need to somehow replace `return H_TOO_HARD` in this patch with code that could call vhost_process_iotlb_msg() with VHOST_IOTLB_INVALIDATE. For that, I would need to know what are the vhost_dev's of that process, which I don't know if it's possible to do currently (or safe at all). I am thinking of linking all vhost_dev's with a list (list.h) that could be searched, comparing `mm_struct *` of the calling task with all vhost_dev's, and removing the entry of all IOTLB that hits. Not sure if that's the best approach to find the related vhost_dev's. What do you think? Best regards, Leonardo Bras
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