Re: [PATCH v6 0/3] Add support for the Idle HLT intercept feature

Manali Shukla
2025-02-17T04:44:23Z

On 2/10/2025 10:36 AM, Manali Shukla wrote:
> On 1/28/2025 6:18 PM, Manali Shukla wrote:
>> The upcoming new Idle HLT Intercept feature allows for the HLT
>> instruction execution by a vCPU to be intercepted by the hypervisor
>> only if there are no pending V_INTR and V_NMI events for the vCPU.
>> When the vCPU is expected to service the pending V_INTR and V_NMI
>> events, the Idle HLT intercept won’t trigger. The feature allows the
>> hypervisor to determine if the vCPU is actually idle and reduces
>> wasteful VMEXITs.
>>
>> The Idle HLT intercept feature is used for enlightened guests who wish
>> to securely handle the events. When an enlightened guest does a HLT
>> while an interrupt is pending, hypervisor will not have a way to
>> figure out whether the guest needs to be re-entered or not. The Idle
>> HLT intercept feature allows the HLT execution only if there are no
>> pending V_INTR and V_NMI events.
>>
>> Presence of the Idle HLT Intercept feature is indicated via CPUID
>> function Fn8000_000A_EDX[30].
>>
>> Document for the Idle HLT intercept feature is available at [1].
>>
>> This series is based on kvm-x86/next (eb723766b103) + [2].
>>
>> Testing Done:
>> - Tested the functionality for the Idle HLT intercept feature
>> using selftest ipi_hlt_test.
>> - Tested on normal, SEV, SEV-ES, SEV-SNP guest for the Idle HLT intercept
>> functionality.
>> - Tested the Idle HLT intercept functionality on nested guest.
>>
>> v5 -> v6
>> - Incorporated Neeraj's review comments on selftest.
>>
>> v4 -> v5
>> - Incorporated Sean's review comments on nested Idle HLT intercept support.
>> - Make svm_idle_hlt_test independent of the Idle HLT to run on all hardware.
>>
>> v3 -> v4
>> - Drop the patches to add vcpu_get_stat() into a new series [2].
>> - Added nested Idle HLT intercept support.
>>
>> v2 -> v3
>> - Incorporated Andrew's suggestion to structure vcpu_stat_types in
>> a way that each architecture can share the generic types and also
>> provide its own.
>>
>> v1 -> v2
>> - Did changes in svm_idle_hlt_test based on the review comments from Sean.
>> - Added an enum based approach to get binary stats in vcpu_get_stat() which
>> doesn't use string to get stat data based on the comments from Sean.
>> - Added safe_halt() and cli() helpers based on the comments from Sean.
>>
>> [1]: AMD64 Architecture Programmer's Manual Pub. 24593, April 2024,
>> Vol 2, 15.9 Instruction Intercepts (Table 15-7: IDLE_HLT).
>> https://bugzilla.kernel.org/attachment.cgi?id=306251
>>
>> [2]: https://lore.kernel.org/kvm/ee027335-f1b9-4637-bc79-27a610c1ab08@amd.com/T/#u
>>
>> ---
>> V5: https://lore.kernel.org/kvm/20250103081828.7060-1-manali.shukla@amd.com/
>> V4: https://lore.kernel.org/kvm/20241022054810.23369-1-manali.shukla@amd.com/
>> V3: https://lore.kernel.org/kvm/20240528041926.3989-4-manali.shukla@amd.com/T/
>> V2: https://lore.kernel.org/kvm/20240501145433.4070-1-manali.shukla@amd.com/
>> V1: https://lore.kernel.org/kvm/20240307054623.13632-1-manali.shukla@amd.com/
>>
>> Manali Shukla (3):
>> x86/cpufeatures: Add CPUID feature bit for Idle HLT intercept
>> KVM: SVM: Add Idle HLT intercept support
>> KVM: selftests: Add self IPI HLT test
>>
>> arch/x86/include/asm/cpufeatures.h | 1 +
>> arch/x86/include/asm/svm.h | 1 +
>> arch/x86/include/uapi/asm/svm.h | 2 +
>> arch/x86/kvm/svm/svm.c | 13 ++-
>> tools/testing/selftests/kvm/Makefile.kvm | 1 +
>> .../selftests/kvm/include/x86/processor.h | 1 +
>> tools/testing/selftests/kvm/ipi_hlt_test.c | 81 +++++++++++++++++++
>> 7 files changed, 97 insertions(+), 3 deletions(-)
>> create mode 100644 tools/testing/selftests/kvm/ipi_hlt_test.c
>>
>>
>> base-commit: eb723766b1030a23c38adf2348b7c3d1409d11f0
>> prerequisite-patch-id: cb345fc0d814a351df2b5788b76eee0eef9de549
>> prerequisite-patch-id: 71806f400cffe09f47d6231cb072cbdbd540de1b
>> prerequisite-patch-id: 9ea0412aab7ecd8555fcee3e9609dbfe8456d47b
>> prerequisite-patch-id: 3504df50cdd33958456f2e56139d76867273525c
>> prerequisite-patch-id: 674e56729a56cc487cb85be1a64ef561eb7bac8a
>> prerequisite-patch-id: 48e87354f9d6e6bd121ca32ab73cd0d7f1dce74f
>> prerequisite-patch-id: b32c21df6522a7396baa41d62bcad9479041d97a
>> prerequisite-patch-id: 0ff4b504e982db7c1dfa8ec6ac485c92a89f4af8
>> prerequisite-patch-id: 509018dc2fc1657debc641544e86f5a92d04bc1a
>
> A gentle reminder for the review.
>
> -Manali
>
>

A gentle reminder for the review.

-Manali