Re: [PATCH v3 00/15] Make RamDiscardManager work with multiple sources

[Chenyi Qiang <chenyi.qiang@intel.com>]

On 3/11/2026 12:09 AM, Marc-André Lureau wrote:
> Hi
> 
> On Tue, Mar 10, 2026 at 6:35 AM Chenyi Qiang <chenyi.qiang@intel.com> wrote:
>>
>>
>>
>> On 2/26/2026 9:59 PM, marcandre.lureau@redhat.com wrote:
>>> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>>>
>>> Hi,
>>>
>>> This is an attempt to fix the incompatibility of virtio-mem with confidential
>>> VMs. The solution implements what was discussed earlier with D. Hildenbrand:
>>> https://patchwork.ozlabs.org/project/qemu-devel/patch/20250407074939.18657-5-chenyi.qiang@intel.com/#3502238
>>>
>>> The first patches are misc cleanups. Then some code refactoring to have split a
>>> manager/source. And finally, the manager learns to deal with multiple sources.
>>>
>>> I haven't done thorough testing. I only launched a SEV guest with a virtio-mem
>>> device. It would be nice to have more tests for those scenarios with
>>> VFIO/virtio-mem/confvm.. In any case, review & testing needed!
>>
>> Is this series aimed to enable virtio-mem (memory hotplug) in a confidential VM?
>> I tested it within a TD guest using the qemu command:
>>
>> qemu-system-x86_64
>>         ...
>>         -m 2G,maxmem=10G \
>>         -smp sockets=1,cores=2 \
>>         -object memory-backend-ram,id=mem0,size=2G \
>>         -numa node,nodeid=0,cpus=0-1,memdev=mem0 \
>>         -object memory-backend-ram,id=vmem0,size=8G \
>>         -device virtio-mem-pci,id=vm0,memdev=vmem0,node=0,requested-size=300M \
>>         -object tdx-guest,id=tdx \
>>         -machine q35,kernel_irqchip=split,hpet=off,memory-encryption=tdx \
>>         ...
>>
>> The TD VM will exit with the error when the guest kernel loads the virtio-mem driver:
>>
>>     kvm_intel: Guest access before accepting 0x108008000 on vCPU 0
>>
>> I think it still lacks some support to accept the TD guest memory before using it.
>>
> 
> It becomes increasingly hard to provide easy to setup reproducibe
> environments.. but here is the libvirt qemu command I just tested
> succesfully against:
> 
> qemu-system-x86_64 -name guest=rhel10,debug-threads=on -S -object
> {"qom-type":"secret","id":"masterKey0","format":"raw","file":"/home/elmarco/.config/libvirt/qemu/lib/domain-3-rhel10/master-key.aes"}
> -machine pc-q35-10.1,usb=off,smm=off,dump-guest-core=off,confidential-guest-support=lsec0,hpet=off,acpi=on
> -accel kvm -cpu host,migratable=on -bios
> /usr/share/edk2/ovmf/OVMF.inteltdx.fd -m
> size=4096000k,slots=1,maxmem=8192000k -overcommit mem-lock=off -smp
> 2,sockets=2,cores=1,threads=1 -object
> {"qom-type":"memory-backend-ram","id":"ram-node0","size":4194304000}
> -numa node,nodeid=0,cpus=0-1,memdev=ram-node0 -uuid
> 0f3e6b74-80e3-45e7-a0e6-ae7dfc897606 -display none -no-user-config
> -nodefaults -chardev socket,id=charmonitor,fd=23,server=on,wait=off
> -mon chardev=charmonitor,id=monitor,mode=control -rtc
> base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay
> -no-shutdown -global ICH9-LPC.disable_s3=1 -global
> ICH9-LPC.disable_s4=1 -boot strict=on -device
> {"driver":"pcie-root-port","port":8,"chassis":1,"id":"pci.1","bus":"pcie.0","multifunction":true,"addr":"0x1"}
> -device {"driver":"pcie-root-port","port":9,"chassis":2,"id":"pci.2","bus":"pcie.0","addr":"0x1.0x1"}
> -device {"driver":"pcie-root-port","port":10,"chassis":3,"id":"pci.3","bus":"pcie.0","addr":"0x1.0x2"}
> -device {"driver":"pcie-root-port","port":11,"chassis":4,"id":"pci.4","bus":"pcie.0","addr":"0x1.0x3"}
> -device {"driver":"pcie-root-port","port":12,"chassis":5,"id":"pci.5","bus":"pcie.0","addr":"0x1.0x4"}
> -device {"driver":"pcie-root-port","port":13,"chassis":6,"id":"pci.6","bus":"pcie.0","addr":"0x1.0x5"}
> -device {"driver":"pcie-root-port","port":14,"chassis":7,"id":"pci.7","bus":"pcie.0","addr":"0x1.0x6"}
> -device {"driver":"pcie-root-port","port":15,"chassis":8,"id":"pci.8","bus":"pcie.0","addr":"0x1.0x7"}
> -device {"driver":"pcie-root-port","port":16,"chassis":9,"id":"pci.9","bus":"pcie.0","multifunction":true,"addr":"0x2"}
> -device {"driver":"pcie-root-port","port":17,"chassis":10,"id":"pci.10","bus":"pcie.0","addr":"0x2.0x1"}
> -device {"driver":"pcie-root-port","port":18,"chassis":11,"id":"pci.11","bus":"pcie.0","addr":"0x2.0x2"}
> -device {"driver":"pcie-root-port","port":19,"chassis":12,"id":"pci.12","bus":"pcie.0","addr":"0x2.0x3"}
> -device {"driver":"pcie-root-port","port":20,"chassis":13,"id":"pci.13","bus":"pcie.0","addr":"0x2.0x4"}
> -device {"driver":"pcie-root-port","port":21,"chassis":14,"id":"pci.14","bus":"pcie.0","addr":"0x2.0x5"}
> -device {"driver":"qemu-xhci","p2":15,"p3":15,"id":"usb","bus":"pci.2","addr":"0x0"}
> -device {"driver":"virtio-serial-pci","id":"virtio-serial0","bus":"pci.3","addr":"0x0"}
> -object {"qom-type":"memory-backend-ram","id":"memvirtiomem0","reserve":false,"size":4194304000}
> -device {"driver":"virtio-mem-pci","node":0,"block-size":2097152,"memdev":"memvirtiomem0","id":"virtiomem0","bus":"pci.7","addr":"0x0"}
> -blockdev {"driver":"file","filename":"/home/elmarco/rhel-10.qcow2","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}
> -blockdev {"node-name":"libvirt-1-format","read-only":false,"driver":"qcow2","file":"libvirt-1-storage","backing":null}
> -device {"driver":"virtio-blk-pci","bus":"pci.4","addr":"0x0","drive":"libvirt-1-format","id":"virtio-disk0","bootindex":1}
> -netdev {"type":"user","id":"hostnet0"} -device
> {"driver":"virtio-net-pci","netdev":"hostnet0","id":"net0","mac":"52:54:00:82:08:40","bus":"pci.1","addr":"0x0"}
> -chardev pty,id=charserial0 -device
> {"driver":"isa-serial","chardev":"charserial0","id":"serial0","index":0}
> -chardev socket,id=charchannel0,fd=22,server=on,wait=off -device
> {"driver":"virtserialport","bus":"virtio-serial0.0","nr":1,"chardev":"charchannel0","id":"channel0","name":"org.qemu.guest_agent.0"}
> -chardev socket,id=chrtpm,path=/run/user/1006/libvirt/qemu/run/swtpm/3-rhel10-swtpm.sock
> -tpmdev emulator,id=tpm-tpm0,chardev=chrtpm -device
> {"driver":"tpm-crb","tpmdev":"tpm-tpm0","id":"tpm0"} -audiodev
> {"id":"audio1","driver":"none"} -global ICH9-LPC.noreboot=off
> -watchdog-action reset -device
> {"driver":"virtio-balloon-pci","id":"balloon0","bus":"pci.5","addr":"0x0"}
> -object {"qom-type":"rng-random","id":"objrng0","filename":"/dev/urandom"}
> -device {"driver":"virtio-rng-pci","rng":"objrng0","id":"rng0","bus":"pci.6","addr":"0x0"}
> -object {"qom-type":"tdx-guest","id":"lsec0","quote-generation-socket":{"type":"unix","path":"/var/run/tdx-qgs/qgs.socket"},"attributes":268435456}
> -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny
> -msg timestamp=on
> 
> Then I hotplugged some mem:
> virsh --connect qemu:///session update-memory-device rhel10
> --requested-size 2GiB
> 
> [  166.228943] virtio_mem virtio5: plugged size: 0x0
> [  166.231784] virtio_mem virtio5: requested size: 0x80000000
> 
> 
> [root@rhel10-server ~]# lsmem
> RANGE                                 SIZE  STATE REMOVABLE BLOCK
> 0x0000000000000000-0x000000007fffffff   2G online       yes  0-15
> 0x0000000100000000-0x00000001ffffffff   4G online       yes 32-63
> 
> Memory block size:       128M
> Total online memory:       6G
> Total offline memory:      0B
> 
> The host kernel used is experimental; it's a patched version of
> 6.19.0-rc8 that I don't have the details)

It seems related to the memory size. Maybe you can have a try with "-m 2G,maxmem=4G".
I hit the problem when the size <= 2G and no range above 4g at the beginning.