> 2020年5月14日 20:19，David Hildenbrand <david@xxxxxxxxxx> 写道： > > On 14.05.20 13:47, David Hildenbrand wrote: >> On 14.05.20 13:10, David Hildenbrand wrote: >>> On 14.05.20 12:12, David Hildenbrand wrote: >>>> On 14.05.20 12:02, teawater wrote: >>>>> >>>>> >>>>>> 2020年5月14日 16:48，David Hildenbrand <david@xxxxxxxxxx> 写道： >>>>>> >>>>>> On 14.05.20 08:44, teawater wrote: >>>>>>> Hi David, >>>>>>> >>>>>>> I got a kernel warning with v2 and v3. >>>>>> >>>>>> Hi Hui, >>>>>> >>>>>> thanks for playing with the latest versions. Surprisingly, I can >>>>>> reproduce even by hotplugging a DIMM instead as well - that's good, so >>>>>> it's not related to virtio-mem, lol. Seems to be some QEMU setup issue >>>>>> with older machine types. >>>>>> >>>>>> Can you switch to a newer qemu machine version, especially >>>>>> pc-i440fx-5.0? Both, hotplugging DIMMs and virtio-mem works for me with >>>>>> that QEMU machine just fine. >>>>> >>>>> I still could reproduce this issue with pc-i440fx-5.0 or pc. Did I miss anything? >>>>> >>>> >>>> Below I don't even see virtio_mem. I had to repair the image (filesystem >>>> fsck) because it was broken, can you try that as well? >>>> >>>> Also, it would be great if you could test with v4. >>>> >>> >>> Correction, something seems to be broken either in QEMU or the kernel. Once I >>> define a DIMM so it's added and online during boot, I get these issues: >>> >>> (I have virtio-mem v4 installed in the guest) >>> >>> #! /bin/bash >>> sudo x86_64-softmmu/qemu-system-x86_64 \ >>> -machine pc-i440fx-5.0,accel=kvm,usb=off \ >>> -cpu host \ >>> -no-reboot \ >>> -nographic \ >>> -device ide-hd,drive=hd \ >>> -drive if=none,id=hd,file=/home/dhildenb/git/Fedora-Cloud-Base-31-1.9.x86_64.qcow2,format=qcow2 \ >>> -m 1g,slots=10,maxmem=2G \ >>> -smp 1 \ >>> -object memory-backend-ram,id=mem0,size=256m \ >>> -device pc-dimm,id=dimm0,memdev=mem0 \ >>> -s \ >>> -monitor unix:/var/tmp/monitor,server,nowait >>> >>> >>> Without the DIMM it seems to work just fine. >>> >> >> And another correction. >> >> Using QEMU v5.0.0, Linux 5.7-rc5, untouched >> Fedora-Cloud-Base-32-1.6.x86_64.qcow2, I get even without any memory hotplug: >> >> #! /bin/bash >> sudo x86_64-softmmu/qemu-system-x86_64 \ >> -machine pc-i440fx-5.0,accel=kvm,usb=off \ >> -cpu host \ >> -no-reboot \ >> -nographic \ >> -device ide-hd,drive=hd \ >> -drive if=none,id=hd,file=/home/dhildenb/git/Fedora-Cloud-Base-32-1.6.x86_64.qcow2,format=qcow2 \ >> -m 5g,slots=10,maxmem=6G \ >> -smp 1 \ >> -s \ >> -kernel /home/dhildenb/git/linux/arch/x86/boot/bzImage \ >> -append "console=ttyS0 rd.shell nokaslr swiotlb=noforce" \ >> -monitor unix:/var/tmp/monitor,server,nowait >> >> >> Observe how big the initial RAM even is! >> >> >> So this is no DIMM/hotplug/virtio_mem issue. With memory hotplug, it seems to get >> more likely to trigger if "swiotlb=noforce" is not specified. >> >> "swiotlb=noforce" seems to trigger some pre-existing issue here. Without >> "swiotlb=noforce", I was only able to observe this via pc-i440fx-2.1, >> > > (talking to myself :) ) > > I think I finally understood why using "swiotlb=noforce" with hotplugged > memory is wrong - or with memory > 3GB. Via "swiotlb=noforce" you tell > the system to "Never use bounce buffers (for debugging)". This works as > long as all memory is DMA memory (e.g., < 3GB) AFAIK. > > "If specified, trying to map memory that cannot be used with DMA will > fail, and a rate-limited warning will be printed." > > Hotplugged memory (under QEMU) is never added below 4GB, because of the > PCI hole. So both, memory from DIMMs and from virtio-mem will end up at > or above 4GB. To make a device use that memory, you need bounce buffers. > > Hotplugged memory is never DMA memory. > Hi David, It is fixed when I remove "swiotlb=noforce”. Thanks for your help. Best, Hui > -- > Thanks, > > David / dhildenb
