On 05.06.20 11:08, David Hildenbrand wrote: > On 05.06.20 10:55, Alex Shi wrote: >> >> >> 在 2020/1/9 下午9:48, David Hildenbrand 写道: >>> Ping, >>> >>> I'd love to get some feedback on >>> >>> a) The remaining MM bits from MM folks (especially, patch #6 and #8). >>> b) The general virtio infrastructure (esp. uapi in patch #2) from virtio >>> folks. >>> >>> I'm planning to send a proper v1 (!RFC) once I have all necessary MM >>> acks. In the meanwhile, I will do more testing and minor reworks (e.g., >>> fix !CONFIG_NUMA compilation). >> >> >> Hi David, >> >> Thanks for your work! >> >> I am trying your https://github.com/davidhildenbrand/linux.git virtio-mem-v5 >> which works fine for me, but just a 'DMA error' happens when a vm start with >> less than 2GB memory, Do I missed sth? > > Please use the virtio-mem-v4 branch for now, v5 is still under > construction (and might be scrapped completely if v4 goes upstream as is). > > Looks like a DMA issue. Your're hotplugging 1GB, which should not really > eat too much memory. There was a similar issue reported by Hui in [1], > which boiled down to wrong usage of the swiotlb parameter. > > In such cases you should always try to reproduce with hotplug of a > sam-sized DIMM. E.g., hotplugging a 1GB DIMM should result in the same > issue. > > What does your .config specify for CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE? > > I'll try to reproduce with v4 briefly. I guess I know what's happening here. In case we only have DMA memory when booting, we don't reserve swiotlb buffers. Once we hotplug memory and online ZONE_NORMAL, we don't have any swiotlb DMA bounce buffers to map such PFNs (total 0 (slots), used 0 (slots)). Can you try with "swiotlb=force" on the kernel cmdline? -- Thanks, David / dhildenb
