linux-kernel - Re: [PATCH kvm-next V11 0/7] Add NUMA mempolicy support for KVM guest-memfd

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Message-ID: <b4abbdfa-8a4e-4c2b-a979-f940fcab37aa@amd.com>
Date: Wed, 24 Sep 2025 15:35:12 -0500
From: "Kalra, Ashish" <ashish.kalra@....com>
To: David Hildenbrand <david@...hat.com>, Shivank Garg <shivankg@....com>,
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Subject: Re: [PATCH kvm-next V11 0/7] Add NUMA mempolicy support for KVM
 guest-memfd

Tested the patch series by auditing the actual userspace (HVA) mappings and seeing if the
corresponding physical PFNs correspond to the expected NUMA node.

Enabled QEMU's kvm_set_user_memory tracepoint to dump the HVA/guest_memfd/guest_memfd_offset/base GPA/size.
This helped determine the HVAs and the memslot that QEMU registers with KVM via the kvm_set_user_memory_region() helper.

After that dumped the PFNs getting mapped into the guest for a particular GPA via enabling the
kvm_mmu_set_spte kernel trace events, performed the GPA->memslot->HVA mapping (via QEMU traces above) and then looked in 
/proc/<qemu_pid>/numa_maps to validate the HVA is bound to the NUMA node associated with that memslot/guest_memfd.
 
Additionally, looked up the PFN (from kernel traces) in /proc/zoneinfo to validate that the physical page belongs to the
NUMA node associated with the memslot/guest_memfd.


This testing/validation is based on the following trees:

Host Kernel: 

https://github.com/AMDESE/linux/commits/snp-hugetlb-v2-wip0/

This tree is based on commit 27cb583e25d0 from David Hildenbrand's guestmemfd_preview tree
(which already includes base mmap support) with Google's HugeTLB v2 patches rebased on top of those
(which include both in-place conversion and hugetlb infrastructure), along with additional
patches to enable in-place conversion and hugetlb for SNP.

QEMU:

https://github.com/AMDESE/qemu/commits/snp-hugetlb-dev-wip0/
   
QEMU command line used for testing/validation:

qemu-system-x86_64 --enable-kvm -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1,convert-in-place=true
-object memory-backend-memfd,id=ram0,host-nodes=0,policy=bind,size=150000M,prealloc=false 
-numa node,nodeid=0,memdev=ram0,cpus=0-31,cpus=64-95 
-object memory-backend-memfd,id=ram1,host-nodes=1,policy=bind,size=150000M,prealloc=false
-numa node,nodeid=1,memdev=ram1,cpus=32-63,cpus=96-127 

(guest NUMA configuration mapped 1:1 to host NUMA configuration).

Tested-by: Ashish Kalra <ashish.kalra@....com>

Thanks,
Ashish

On 9/24/2025 1:19 PM, David Hildenbrand wrote:
> On 27.08.25 19:52, Shivank Garg wrote:
>> This series introduces NUMA-aware memory placement support for KVM guests
>> with guest_memfd memory backends. It builds upon Fuad Tabba's work (V17)
>> that enabled host-mapping for guest_memfd memory [1] and can be applied
>> directly applied on KVM tree [2] (branch kvm-next, base commit: a6ad5413,
>> Merge branch 'guest-memfd-mmap' into HEAD)
>>
> 
> Heads-up: I'll queue this (incl. the replacement patch for #4 from the reply) and send it tomorrow as a PR against kvm/next to Paolo.
>