On 6/27/2025 9:55 PM, Manali Shukla wrote: > Add support for IBS virtualization (VIBS). VIBS feature allows the > guest to collect IBS samples without exiting the guest. There are > 2 parts to it [1]. > - Virtualizing the IBS register state. > - Ensuring the IBS interrupt is handled in the guest without exiting > the hypervisor. > > To deliver virtualized IBS interrupts to the guest, VIBS requires either > AVIC or Virtual NMI (VNMI) support [1]. During IBS sampling, the > hardware signals a VNMI. The source of this VNMI depends on the AVIC > configuration: > > - With AVIC disabled, the virtual NMI is hardware-accelerated. > - With AVIC enabled, the virtual NMI is delivered via AVIC using Extended LVT. > > The local interrupts are extended to include more LVT registers, to > allow additional interrupt sources, like instruction based sampling > etc. [3]. > > Although IBS virtualization requires either AVIC or VNMI to be enabled > in order to successfully deliver IBS NMIs to the guest, VNMI must be > enabled to ensure reliable delivery. This requirement stems from the > dynamic behavior of AVIC. While a guest is launched with AVIC enabled, > AVIC can be inhibited at runtime. When AVIC is inhibited and VNMI is > disabled, there is no mechanism to deliver IBS NMIs to the guest. > Therefore, enabling VNMI is necessary to support IBS virtualization > reliably. > > Note that, since IBS registers are swap type C [2], the hypervisor is > responsible for saving and restoring of IBS host state. Hypervisor needs > to disable host IBS before saving the state and enter the guest. After a > guest exit, the hypervisor needs to restore host IBS state and re-enable > IBS. > > The mediated PMU has the capability to save the host context when > entering the guest by scheduling out all exclude_guest events, and to > restore the host context when exiting the guest by scheduling in the > previously scheduled-out events. This behavior aligns with the > requirement for IBS registers being of swap type C. Therefore, the > mediated PMU design can be leveraged to implement IBS virtualization. > As a result, enabling the mediated PMU is a necessary requirement for > IBS virtualization. > > The initial version of this series has been posted here: > https://lore.kernel.org/kvm/f98687e0-1fee-8208-261f-d93152871f00@xxxxxxx/ > > Since then, the mediated PMU patches [5] have matured significantly. > This series is a resurrection of previous VIBS series and leverages the > mediated PMU infrastructure to enable IBS virtualization. > > How to enable VIBS? > ---------------------------------------------- > sudo echo 0 | sudo tee /proc/sys/kernel/nmi_watchdog > sudo modprobe -r kvm_amd > sudo modprobe kvm_amd enable_mediated_pmu=1 vnmi=1 > > Qemu changes can be found at below location: > ---------------------------------------------- > https://github.com/AMDESE/qemu/tree/vibs_v1 > > Qemu commandline to enable IBS virtualization: > ------------------------------------------------ > qemu-system-x86_64 -enable-kvm -cpu EPYC-Genoa,+ibs,+extlvt,+extapic,+svm,+pmu \ .. > > Testing done: > ------------------------------------------------ > - Following tests were executed on guest > sudo perf record -e ibs_op// -c 100000 -a > sudo perf record -e ibs_op// -c 100000 -C 10 > sudo perf record -e ibs_op/cnt_ctl=1/ -c 100000 -a > sudo perf record -e ibs_op/cnt_ctl=1/ -c 100000 -a --raw-samples > sudo perf record -e ibs_op/cnt_ctl=1,l3missonly=1/ -c 100000 -a > sudo perf record -e ibs_op/cnt_ctl=1/ -c 100000 -p 1234 > sudo perf record -e ibs_op/cnt_ctl=1/ -c 100000 -- ls > sudo ./tools/perf/perf record -e ibs_op// -e ibs_fetch// -a --raw-samples -c 100000 > sudo perf report > sudo perf script > sudo perf report -D | grep -P "LdOp 1.*StOp 0" | wc -l > sudo perf report -D | grep -P "LdOp 1.*StOp 0.*DcMiss 1" | wc -l > sudo perf report -D | grep -P "LdOp 1.*StOp 0.*DcMiss 1.*L2Miss 1" | wc -l > sudo perf report -D | grep -B1 -P "LdOp 1.*StOp 0.*DcMiss 1.*L2Miss 1" | grep -P "DataSrc ([02-9]|1[0-2])=" | wc -l > - perf_fuzzer was run for 3hrs, no softlockups or unknown NMIs were > seen. > > TO-DO: > ----------------------------------- > Enable IBS virtualization on SEV-ES and SEV-SNP guests. > > base-commit (61374cc145f4) + [4] (Clean up KVM's MSR interception code) > + [5] (Mediated vPMU 4.0 for x86). > > [1]: https://bugzilla.kernel.org/attachment.cgi?id=306250 > AMD64 Architecture Programmer’s Manual, Vol 2, Section 15.38 > Instruction-Based Sampling Virtualization. > > [2]: https://bugzilla.kernel.org/attachment.cgi?id=306250 > AMD64 Architecture Programmer’s Manual, Vol 2, Appendix B Layout > of VMCB, Table B-3 Swap Types. > > [3]: https://bugzilla.kernel.org/attachment.cgi?id=306250 > AMD64 Architecture Programmer’s Manual, Vol 2, Section 16.4.5 > Extended Interrupts. > > [4]: https://lore.kernel.org/kvm/20250610225737.156318-1-seanjc@xxxxxxxxxx/ > > [5]: https://lore.kernel.org/kvm/20250324173121.1275209-1-mizhang@xxxxxxxxxx/ > > Manali Shukla (6): > perf/amd/ibs: Fix race condition in IBS > KVM: Add KVM_GET_LAPIC_W_EXTAPIC and KVM_SET_LAPIC_W_EXTAPIC for > extapic > KVM: x86/cpuid: Add a KVM-only leaf for IBS capabilities > KVM: x86: Extend CPUID range to include new leaf > perf/x86/amd: Enable VPMU passthrough capability for IBS PMU > perf/x86/amd: Remove exclude_guest check from perf_ibs_init() > > Santosh Shukla (5): > x86/cpufeatures: Add CPUID feature bit for Extended LVT > KVM: x86: Add emulation support for Extented LVT registers > x86/cpufeatures: Add CPUID feature bit for VIBS in SVM/SEV guests > KVM: SVM: Extend VMCB area for virtualized IBS registers > KVM: SVM: Add support for IBS Virtualization > > Documentation/virt/kvm/api.rst | 23 +++++++ > arch/x86/events/amd/ibs.c | 8 ++- > arch/x86/include/asm/apicdef.h | 17 ++++++ > arch/x86/include/asm/cpufeatures.h | 2 + > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/include/asm/svm.h | 16 ++++- > arch/x86/include/uapi/asm/kvm.h | 5 ++ > arch/x86/kvm/cpuid.c | 13 ++++ > arch/x86/kvm/lapic.c | 81 ++++++++++++++++++++++--- > arch/x86/kvm/lapic.h | 7 ++- > arch/x86/kvm/reverse_cpuid.h | 16 +++++ > arch/x86/kvm/svm/avic.c | 4 ++ > arch/x86/kvm/svm/svm.c | 96 ++++++++++++++++++++++++++++++ > arch/x86/kvm/x86.c | 37 ++++++++---- > include/uapi/linux/kvm.h | 10 ++++ > 15 files changed, 313 insertions(+), 23 deletions(-) > > > base-commit: 61374cc145f4a56377eaf87c7409a97ec7a34041 A gentle reminder for the review. -Manali
