Re: [PATCH v5 00/44] KVM: x86: Add support for mediated vPMUs

Mi, Dapeng
2025-08-08T08:35:49Z

On 8/8/2025 4:28 PM, Mi, Dapeng wrote:
> On 8/7/2025 3:56 AM, Sean Christopherson wrote:
>> This series is based on the fastpath+PMU cleanups series[*] (which is based on
>> kvm/queue), but the non-KVM changes apply cleanly on v6.16 or Linus' tree.
>> I.e. if you only care about the perf changes, I would just apply on whatever
>> branch is convenient and stop when you hit the KVM changes.
>>
>> My hope/plan is that the perf changes will go through the tip tree with a
>> stable tag/branch, and the KVM changes will go the kvm-x86 tree.
>>
>> Non-x86 KVM folks, y'all are getting Cc'd due to minor changes in "KVM: Add a
>> simplified wrapper for registering perf callbacks".
>>
>> The full set is also available at:
>>
>> https://github.com/sean-jc/linux.git tags/mediated-vpmu-v5
>>
>> Add support for mediated vPMUs in KVM x86, where "mediated" aligns with the
>> standard definition of intercepting control operations (e.g. event selectors),
>> while allowing the guest to perform data operations (e.g. read PMCs, toggle
>> counters on/off) without KVM getting involed.
>>
>> For an in-depth description of the what and why, please see the cover letter
>> from the original RFC:
>>
>> https://lore.kernel.org/all/20240126085444.324918-1-xiong.y.zhang@linux.intel.com
>>
>> All KVM tests pass (or fail the same before and after), and I've manually
>> verified MSR/PMC are passed through as expected, but I haven't done much at all
>> to actually utilize the PMU in a guest. I'll be amazed if I didn't make at
>> least one major goof.
>>
>> Similarly, I tried to address all feedback, but there are many, many changes
>> relative to v4. If I missed something, I apologize in advance.
>>
>> In other words, please thoroughly review and test.
> Went through the whole patchset, it looks good to me.
>
> Run all PMU related kselftests and KUT tests on Intel Sapphire Rapids, no
> issue is found. We would run broader tests on more Intel platforms. Thanks.

Forgot to say "all tests are run for both mediated vPMU and the legacy
perf-based vPMU, no issue is found". Thanks.

>
>
>> [*] https://lore.kernel.org/all/20250805190526.1453366-1-seanjc@google.com
>>
>> v5:
>> - Add a patch to call security_perf_event_free() from __free_event()
>> instead of _free_event() (necessitated by the __cleanup() changes).
>> - Add CONFIG_PERF_GUEST_MEDIATED_PMU to guard the new perf functionality.
>> - Ensure the PMU is fully disabled in perf_{load,put}_guest_context() when
>> when switching between guest and host context. [Kan, Namhyung]
>> - Route the new system IRQ, PERF_GUEST_MEDIATED_PMI_VECTOR, through perf,
>> not KVM, and play nice with FRED.
>> - Rename and combine perf_{guest,host}_{enter,exit}() to a single set of
>> APIs, perf_{load,put}_guest_context().
>> - Rename perf_{get,put}_mediated_pmu() to perf_{create,release}_mediated_pmu()
>> to (hopefully) better differentiate them from perf_{load,put}_guest_context().
>> - Change the param to the load/put APIs from "u32 guest_lvtpc" to
>> "unsigned long data" to decouple arch code as much as possible. E.g. if
>> a non-x86 arch were to ever support a mediated vPMU, @data could be used
>> to pass a pointer to a struct.
>> - Use pmu->version to detect if a vCPU has a mediated PMU.
>> - Use a kvm_x86_ops hook to check for mediated PMU support.
>> - Cull "passthrough" from as many places as I could find.
>> - Improve the changelog/documentation related to RDPMC interception.
>> - Check harware capabilities, not KVM capabilities, when calculating
>> MSR and RDPMC intercepts.
>> - Rework intercept (re)calculation to use a request and the existing (well,
>> will be existing as of 6.17-rc1) vendor hooks for recalculating intercepts.
>> - Always read PERF_GLOBAL_CTRL on VM-Exit if writes weren't intercepted while
>> running the vCPU.
>> - Call setup_vmcs_config() before kvm_x86_vendor_init() so that the golden
>> VMCS configuration is known before kvm_init_pmu_capability() is called.
>> - Keep as much refresh/init code in common x86 as possible.
>> - Context switch PMCs and event selectors in common x86, not vendor code.
>> - Bail from the VM-Exit fastpath if the guest is counting instructions
>> retired and the mediated PMU is enabled (because guest state hasn't yet
>> been synchronized with hardware).
>> - Don't require an userspace to opt-in via KVM_CAP_PMU_CAPABILITY, and instead
>> automatically "create" a mediated PMU on the first KVM_CREATE_VCPU call if
>> the VM has an in-kernel local APIC.
>> - Add entries in kernel-parameters.txt for the PMU params.
>> - Add a patch to elide PMC writes when possible.
>> - Many more fixups and tweaks...
>>
>> v4:
>> - https://lore.kernel.org/all/20250324173121.1275209-1-mizhang@google.com
>> - Rebase whole patchset on 6.14-rc3 base.
>> - Address Peter's comments on Perf part.
>> - Address Sean's comments on KVM part.
>> * Change key word "passthrough" to "mediated" in all patches
>> * Change static enabling to user space dynamic enabling via KVM_CAP_PMU_CAPABILITY.
>> * Only support GLOBAL_CTRL save/restore with VMCS exec_ctrl, drop the MSR
>> save/retore list support for GLOBAL_CTRL, thus the support of mediated
>> vPMU is constrained to SapphireRapids and later CPUs on Intel side.
>> * Merge some small changes into a single patch.
>> - Address Sandipan's comment on invalid pmu pointer.
>> - Add back "eventsel_hw" and "fixed_ctr_ctrl_hw" to avoid to directly
>> manipulate pmc->eventsel and pmu->fixed_ctr_ctrl.
>>
>> v3: https://lore.kernel.org/all/20240801045907.4010984-1-mizhang@google.com
>> v2: https://lore.kernel.org/all/20240506053020.3911940-1-mizhang@google.com
>> v1: https://lore.kernel.org/all/20240126085444.324918-1-xiong.y.zhang@linux.intel.com
>>
>> Dapeng Mi (15):
>> KVM: x86/pmu: Start stubbing in mediated PMU support
>> KVM: x86/pmu: Implement Intel mediated PMU requirements and
>> constraints
>> KVM: x86: Rename vmx_vmentry/vmexit_ctrl() helpers
>> KVM: x86/pmu: Move PMU_CAP_{FW_WRITES,LBR_FMT} into msr-index.h header
>> KVM: VMX: Add helpers to toggle/change a bit in VMCS execution
>> controls
>> KVM: x86/pmu: Disable RDPMC interception for compatible mediated vPMU
>> KVM: x86/pmu: Load/save GLOBAL_CTRL via entry/exit fields for mediated
>> PMU
>> KVM: x86/pmu: Use BIT_ULL() instead of open coded equivalents
>> KVM: x86/pmu: Disable interception of select PMU MSRs for mediated
>> vPMUs
>> KVM: x86/pmu: Bypass perf checks when emulating mediated PMU counter
>> accesses
>> KVM: x86/pmu: Reprogram mediated PMU event selectors on event filter
>> updates
>> KVM: x86/pmu: Load/put mediated PMU context when entering/exiting
>> guest
>> KVM: x86/pmu: Handle emulated instruction for mediated vPMU
>> KVM: nVMX: Add macros to simplify nested MSR interception setting
>> KVM: x86/pmu: Expose enable_mediated_pmu parameter to user space
>>
>> Kan Liang (7):
>> perf: Skip pmu_ctx based on event_type
>> perf: Add generic exclude_guest support
>> perf: Add APIs to create/release mediated guest vPMUs
>> perf: Clean up perf ctx time
>> perf: Add a EVENT_GUEST flag
>> perf: Add APIs to load/put guest mediated PMU context
>> perf/x86/intel: Support PERF_PMU_CAP_MEDIATED_VPMU
>>
>> Mingwei Zhang (3):
>> perf/x86/core: Plumb mediated PMU capability from x86_pmu to
>> x86_pmu_cap
>> KVM: x86/pmu: Introduce eventsel_hw to prepare for pmu event filtering
>> KVM: nVMX: Disable PMU MSR interception as appropriate while running
>> L2
>>
>> Sandipan Das (3):
>> perf/x86/core: Do not set bit width for unavailable counters
>> perf/x86/amd: Support PERF_PMU_CAP_MEDIATED_VPMU for AMD host
>> KVM: x86/pmu: Always stuff GuestOnly=1,HostOnly=0 for mediated PMCs on
>> AMD
>>
>> Sean Christopherson (15):
>> perf: Move security_perf_event_free() call to __free_event()
>> perf: core/x86: Register a new vector for handling mediated guest PMIs
>> perf/x86: Switch LVTPC to/from mediated PMI vector on guest load/put
>> context
>> KVM: VMX: Setup canonical VMCS config prior to kvm_x86_vendor_init()
>> KVM: SVM: Check pmu->version, not enable_pmu, when getting PMC MSRs
>> KVM: Add a simplified wrapper for registering perf callbacks
>> KVM: x86/pmu: Snapshot host (i.e. perf's) reported PMU capabilities
>> KVM: x86/pmu: Implement AMD mediated PMU requirements
>> KVM: x86: Rework KVM_REQ_MSR_FILTER_CHANGED into a generic
>> RECALC_INTERCEPTS
>> KVM: x86: Use KVM_REQ_RECALC_INTERCEPTS to react to CPUID updates
>> KVM: x86/pmu: Move initialization of valid PMCs bitmask to common x86
>> KVM: x86/pmu: Restrict GLOBAL_{CTRL,STATUS}, fixed PMCs, and PEBS to
>> PMU v2+
>> KVM: x86/pmu: Disallow emulation in the fastpath if mediated PMCs are
>> active
>> KVM: nSVM: Disable PMU MSR interception as appropriate while running
>> L2
>> KVM: x86/pmu: Elide WRMSRs when loading guest PMCs if values already
>> match
>>
>> Xiong Zhang (1):
>> KVM: x86/pmu: Register PMI handler for mediated vPMU
>>
>> .../admin-guide/kernel-parameters.txt | 49 ++
>> arch/arm64/kvm/arm.c | 2 +-
>> arch/loongarch/kvm/main.c | 2 +-
>> arch/riscv/kvm/main.c | 2 +-
>> arch/x86/entry/entry_fred.c | 1 +
>> arch/x86/events/amd/core.c | 2 +
>> arch/x86/events/core.c | 32 +-
>> arch/x86/events/intel/core.c | 5 +
>> arch/x86/include/asm/hardirq.h | 3 +
>> arch/x86/include/asm/idtentry.h | 6 +
>> arch/x86/include/asm/irq_vectors.h | 4 +-
>> arch/x86/include/asm/kvm-x86-ops.h | 2 +-
>> arch/x86/include/asm/kvm-x86-pmu-ops.h | 4 +
>> arch/x86/include/asm/kvm_host.h | 7 +-
>> arch/x86/include/asm/msr-index.h | 17 +-
>> arch/x86/include/asm/perf_event.h | 1 +
>> arch/x86/include/asm/vmx.h | 1 +
>> arch/x86/kernel/idt.c | 3 +
>> arch/x86/kernel/irq.c | 19 +
>> arch/x86/kvm/Kconfig | 1 +
>> arch/x86/kvm/cpuid.c | 2 +
>> arch/x86/kvm/pmu.c | 272 ++++++++-
>> arch/x86/kvm/pmu.h | 37 +-
>> arch/x86/kvm/svm/nested.c | 18 +-
>> arch/x86/kvm/svm/pmu.c | 51 +-
>> arch/x86/kvm/svm/svm.c | 54 +-
>> arch/x86/kvm/vmx/capabilities.h | 11 +-
>> arch/x86/kvm/vmx/main.c | 14 +-
>> arch/x86/kvm/vmx/nested.c | 65 ++-
>> arch/x86/kvm/vmx/pmu_intel.c | 169 ++++--
>> arch/x86/kvm/vmx/pmu_intel.h | 15 +
>> arch/x86/kvm/vmx/vmx.c | 143 +++--
>> arch/x86/kvm/vmx/vmx.h | 11 +-
>> arch/x86/kvm/vmx/x86_ops.h | 2 +-
>> arch/x86/kvm/x86.c | 69 ++-
>> arch/x86/kvm/x86.h | 1 +
>> include/linux/kvm_host.h | 11 +-
>> include/linux/perf_event.h | 38 +-
>> init/Kconfig | 4 +
>> kernel/events/core.c | 521 ++++++++++++++----
>> .../beauty/arch/x86/include/asm/irq_vectors.h | 3 +-
>> virt/kvm/kvm_main.c | 6 +-
>> 42 files changed, 1385 insertions(+), 295 deletions(-)
>>
>>
>> base-commit: 53d61a43a7973f812caa08fa922b607574befef4