Stefan Hajnoczi <stefa...@redhat.com> writes: > On Fri, Jul 24, 2020 at 10:58:45AM +0000, Alyssa Ross wrote: >> Alyssa Ross <h...@alyssa.is> writes: >> >> > Stefan Hajnoczi <stefa...@redhat.com> writes: >> > >> >> On Tue, Jul 21, 2020 at 07:14:38AM +0000, Alyssa Ross wrote: >> >>> Hi -- I hope it's okay me reaching out like this. >> >>> >> >>> I've been trying to test out the virtio-vhost-user implementation that's >> >>> been posted to this list a couple of times, but have been unable to get >> >>> it to boot a kernel following the steps listed either on >> >>> <https://wiki.qemu.org/Features/VirtioVhostUser> or >> >>> <https://ndragazis.github.io/dpdk-vhost-vvu-demo.html>. >> >>> >> >>> Specifically, the kernel appears to be unable to write to the >> >>> virtio-vhost-user device's PCI registers. I've included the full panic >> >>> output from the kernel at the end of this message. The panic is >> >>> reproducible with two different kernels I tried (with different configs >> >>> and versions). I tried both versions of the virtio-vhost-user I was >> >>> able to find[1][2], and both exhibited the same behaviour. >> >>> >> >>> Is this a known issue? Am I doing something wrong? >> >> >> >> Hi, >> >> Unfortunately I'm not sure what the issue is. This is an early >> >> virtio-pci register access before a driver for any specific device type >> >> (net, blk, vhost-user, etc) comes into play. >> > >> > Small update here: I tried on another computer, and it worked. Made >> > sure that it was exactly the same QEMU binary, command line, and VM >> > disk/initrd/kernel, so I think I can fairly confidently say the panic >> > depends on what hardware QEMU is running on. I set -cpu value to the >> > same on both as well (SandyBridge). >> > >> > I also discovered that it works on my primary computer (the one it >> > panicked on before) with KVM disabled. >> > >> > Note that I've only got so far as finding that it boots on the other >> > machine -- I haven't verified yet that it actually works. >> > >> > Bad host CPU: Intel(R) Core(TM) i5-2520M CPU @ 2.50GHz >> > Good host CPU: AMD EPYC 7401P 24-Core Processor >> > >> > May I ask what host CPUs other people have tested this on? Having more >> > data would probably be useful. Could it be an AMD vs. Intel thing? >> >> I think I've figured it out! >> >> Sandy Bridge and Ivy Bridge hosts encounter this panic because the >> "additional resources" bar size is too big, at 1 << 36. If I change >> this to 1 << 35, no more kernel panic. >> >> Skylake and later are fine with 1 << 36. In between Ivy Bridge and >> Skylake were Haswell and Broadwell, but I couldn't find anybody who was >> able to help me test on either of those, so I don't know what they do. >> >> Perhaps related, the hosts that produce panics all seem to have a >> physical address size of 36 bits, while the hosts that work have larger >> physical address sizes, as reported by lscpu. > > I have run it successfully on Broadwell but never tried 64GB or larger > shared memory resources.
To clarify, I haven't been using big shared memory resources either -- this has all been about getting the backend VM to start at all. The panic happens at boot, and the 1 << 36 BAR allocation comes from here, during realization: https://github.com/ndragazis/qemu/blob/f9ab08c0c8/hw/virtio/virtio-vhost-user-pci.c#L291
