On Fri, Aug 01 2025, Shameer Kolothum <shameerkolot...@gmail.com> wrote:
> 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.) FWIW, all of your mails have made it into my inbox -- let's see if at least my reply shows up on the lists :/ > > 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”. Hm, I *really* need to do a respin of that one, at least to bring it up to date with the code that changed underneath... > > -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. Should that check rather be done by management software on top? Although I assume that this is the part that in practice will come up with the list of possible target cpus. > > -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
