This patch series introduces fbind() syscall to support NUMA memory policies for KVM guest_memfd, allowing VMMs to configure memory placement for guest memory. This addresses the current limitation where guest_memfd allocations ignore NUMA policies, potentially impacting performance of memory-locality-sensitive workloads. Currently, while mbind() enables NUMA policy support for userspace applications, it cannot be used with guest_memfd as the memory isn't mapped to userspace. This results in guest memory being allocated randomly across host NUMA nodes, even when specific policies and node preferences are specified in QEMU commands. The fbind() syscall is particularly useful for SEV-SNP guests. Following suggestions from LPC and review comment [1], I switched from an IOCTL-based approach [2] to fbind() [3]. The fbind() approach is preferred as it provides a generic NUMA policy configuration working with any fd, rather than being tied to guest-memfd. Testing: QEMU tree- https://github.com/AMDESE/qemu/tree/guest_memfd_fbind_NUMA Based upon Github tree- https://github.com/AMDESE/linux/tree/snp-host-latest Branch: snp-host-latest commit: 85ef1ac Example command to run a SEV-SNP guest bound to NUMA Node 0 of the host: $ qemu-system-x86_64 \ -enable-kvm \ ... -machine memory-encryption=sev0,vmport=off \ -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1 \ -numa node,nodeid=0,memdev=ram0,cpus=0-15 \ -object memory-backend-memfd,id=ram0,policy=bind,host-nodes=0,size=1024M,share=true,prealloc=false [1]: https://lore.kernel.org/linux-mm/ZvEga7srKhympQBt@xxxxxxxxx/ [2]: https://lore.kernel.org/linux-mm/20240919094438.10987-1-shivankg@xxxxxxx [3]: https://lore.kernel.org/kvm/ZOjpIL0SFH+E3Dj4@xxxxxxxxxx/ Shivank Garg (3): Introduce fbind syscall KVM: guest_memfd: Pass file pointer instead of inode in guest_memfd APIs KVM: guest_memfd: Enforce NUMA mempolicy if available Shivansh Dhiman (1): mm: Add mempolicy support to the filemap layer arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + include/linux/fs.h | 3 ++ include/linux/mempolicy.h | 3 ++ include/linux/pagemap.h | 40 ++++++++++++++++ include/linux/syscalls.h | 3 ++ include/uapi/asm-generic/unistd.h | 5 +- kernel/sys_ni.c | 1 + mm/Makefile | 2 +- mm/fbind.c | 49 +++++++++++++++++++ mm/filemap.c | 30 ++++++++++-- mm/mempolicy.c | 57 ++++++++++++++++++++++ virt/kvm/guest_memfd.c | 66 +++++++++++++++++++++----- 13 files changed, 242 insertions(+), 19 deletions(-) create mode 100644 mm/fbind.c -- 2.34.1
