From: Shameer Kolothum <shameerali.kolothum.th...@huawei.com> (This is my third attempt to send this series to qemu-devel / qemu-arm. Previous attempts failed with the following errors:
qemu-...@nongnu.org: connect to eggs.gnu.org[209.51.188.92]:25: Connection timed out qemu-devel@nongnu.org: connect to eggs.gnu.org[209.51.188.92]:25: Connection timed out I'm not sure if the issue is related to my setup, so I'm now trying to send the patches via my Gmail account. Apologies if you’ve already received this series individually, and thank you for your patience.) Hi, On ARM64 platforms, many errata workarounds are based on CPU identification registers, particularly MIDR_EL1 and REVIDR_EL1. Some of these errata require corresponding fixes in the guest kernel as well. This becomes a challenge during guest migration between hosts with different MIDR/REVIDR values, even when the VMM provides a common baseline feature set using the recently introduced writable ID register support. To address this, the Linux kernel now provides: -A mechanism to expose implementation CPU data to guests via KVM hypercalls [0]: ARM_SMCCC_VENDOR_HYP_KVM_DISCOVER_IMPL_VER_FUNC_ID ARM_SMCCC_VENDOR_HYP_KVM_DISCOVER_IMPL_CPUS_FUNC_ID -A way to override implementation ID registers (MIDR, REVIDR, AIDR), which were previously treated as invariant [1]. What this RFC does: This RFC enables the virt machine to specify Target Implementation CPUs via QEMU command-line, exposing them to the guest via KVM hypercalls. Example use case (hosts with differing MIDRs): ./qemu-system-aarch64 -machine virt,gic-version=3 \ -enable-kvm \ -bios QEMU_EFI.fd \ -m 1G -smp cpus=4,maxcpus=4 \ -cpu host \ -M impl-cpu.0.midr=0x481fd010,impl-cpu.0.revidr=0,impl-cpu.0.aidr=0x551,\ impl-cpu.1.midr=0x481fd011,impl-cpu.1.revidr=0,impl-cpu.1.aidr=0x551 \ -kernel Image-6.16-rc2 \ -initrd rootfs-iperf.cpio \ -append "rdinit=init console=ttyAMA0 root=/dev/vda rw earlycon=pl011,0x9000000 kpti=off" \ -net none \ -nographic Highlights and Notes: -This is based on Connie’s series[2] “kvm/arm: Introduce a customizable aarch64 KVM host model”. -Currently, no validation is performed on user-specified implementation CPU data. It’s assumed that one of the entries reflects the actual host CPU. If needed, a check can be added to enforce this. All other target CPU definitions are treated as user-driven with no internal verification. -For now, only the DISCOVER_IMPL_* hypercalls are supported on the QEMU side. See patches 1 and 3 for implementation details. These are loosely inspired by Salil's vCPU hotplug series patch here [3]. This may require a more generic approach if we have to support other SMCCC hyper calls. -This series uses macros and definitions from the kernel's include/linux/arm-smccc.h. I am not sure whether these should be duplicated in QEMU or moved to a UAPI header in the kernel. For now I am carrying it in the test branch here, https://github.com/hisilicon/qemu/commit/8f583c76a2a5f60cf0f9616d61d0863e524ef388 This is lightly tested on HiSilicon ARM platforms. A complete test branch can be found here, https://github.com/hisilicon/qemu/tree/arm-cpu-model-rfcv3-tgt-impl-cpu-rfcv1 Please take a look and let me know. Thanks, Shameer [0] https://lore.kernel.org/all/20250221140229.12588-1-shameerali.kolothum.th...@huawei.com/ [1] https://lore.kernel.org/all/20250225005401.679536-1-oliver.up...@linux.dev/ [2] https://lore.kernel.org/qemu-devel/20250414163849.321857-1-coh...@redhat.com/ [3] https://lore.kernel.org/qemu-devel/20240614001510.202991-1-salil.me...@huawei.com/ Shameer Kolothum (4): target/arm/kvm: Introduce helper to check target impl CPU support target/arm/kvm: Add QAPI struct ArmTargetImplCPU target/arm/kvm: Handle KVM Target Imp CPU hypercalls hw/arm/virt: Add Target Implementation CPU support hw/arm/virt.c | 66 +++++++++++++++ include/hw/arm/virt.h | 3 + qapi/machine.json | 34 ++++++++ target/arm/kvm.c | 187 ++++++++++++++++++++++++++++++++++++++++++ target/arm/kvm_arm.h | 20 +++++ 5 files changed, 310 insertions(+) -- 2.34.1
