Yes, that's a bug in virito 0.9, by the way: it should report a 44-bit DMA mask rather than a 64-bit DMA mask. That's on my list of things to upstream. I propose that VMs with more than 2^44=16TB of RAM do not set the "SWIOTLB unneeded bit" -- and that those VMs can tolerate wasting 64MB of RAM. This seems like a not very onerous restriction. Thanks, Ben On Mon, Sep 12, 2016 at 1:14 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > > On 12/09/2016 19:14, Benjamin Serebrin wrote: >> >> One could tie hot plug of a bounce-buffer-requiring virtual device to >> causing SWIOTLB allocation, and fail the device initialization if the >> required buffer couldn't be allocated. I don't know of any new >> virtual devices that require that, though, as high-mem-incapability is >> hopefully only a vestige of very old virtual or real devices. > > There are some devices (most importantly virtio 0.9) that use 32-bit > PFNs. They would require bounce buffers if the physical addresses are at > or above 2^44. > > Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
