On 4/14/2023 2:25 PM, Chao Gao wrote:
Changes since RFC v1:
- add two kselftests (patch 10-11)
- set virtual MSRs also on APs [Pawan]
- enable "virtualize IA32_SPEC_CTRL" for L2 to prevent L2 from changing some bits of IA32_SPEC_CTRL (patch 4)
- other misc cleanup and cosmetic changes
RFC v1: https://lore.kernel.org/lkml/20221210160046.2608762-1-chen.zhang@intel.com/
This series introduces "virtualize IA32_SPEC_CTRL" support. Here are introduction and use cases of this new feature.
### Virtualize IA32_SPEC_CTRL
"Virtualize IA32_SPEC_CTRL" [1] is a new VMX feature on Intel CPUs. This feature allows VMM to lock some bits of IA32_SPEC_CTRL MSR even when the MSR is pass-thru'd to a guest.
### Use cases of "virtualize IA32_SPEC_CTRL" [2]
Software mitigations like Retpoline and software BHB-clearing sequence depend on CPU microarchitectures. And guest cannot know exactly the underlying microarchitecture. When a guest is migrated between processors of different microarchitectures, software mitigations which work perfectly on previous microachitecture may be not effective on the new one. To fix the problem, some hardware mitigations should be used in conjunction with software mitigations.
So even the hardware mitigations are enabled, the software mitigations are still needed, right?
Using virtual IA32_SPEC_CTRL, VMM can enforce hardware mitigations transparently to guests and avoid those hardware mitigations being unintentionally disabled when guest changes IA32_SPEC_CTRL MSR.
### Intention of this series
This series adds the capability of enforcing hardware mitigations for guests transparently and efficiently (i.e., without intecepting IA32_SPEC_CTRL MSR
/s/intecepting/intercepting
accesses) to kvm. The capability can be used to solve the VM migration issue in a pool consisting of processors of different microarchitectures.
Specifically, below are two target scenarios of this series:
Scenario 1: If retpoline is used by a VM to mitigate IMBTI in CPL0, VMM can set RRSBA_DIS_S on parts enumerates RRSBA. Note that the VM is presented with a microarchitecture doesn't enumerate RRSBA.
Scenario 2: If a VM uses software BHB-clearing sequence on transitions into CPL0 to mitigate BHI, VMM can use "virtualize IA32_SPEC_CTRL" to set BHI_DIS_S on new parts which doesn't enumerate BHI_NO.
Intel defines some virtual MSRs [2] for guests to report in-use software mitigations. This allows guests to opt in VMM's deploying hardware mitigations for them if the guests are either running or later migrated to a system on which in-use software mitigations are not effective. The virtual MSRs interface is also added in this series.
### Organization of this series
- Patch 1-3 Advertise RRSBA_CTRL and BHI_CTRL to guest
- Patch 4 Add "virtualize IA32_SPEC_CTRL" support
- Patch 5-9 Allow guests to report in-use software mitigations to KVM so that KVM can enable hardware mitigations for guests.
- Patch 10-11 Add kselftest for virtual MSRs and IA32_SPEC_CTRL
[1]: https://cdrdv2.intel.com/v1/dl/getContent/671368 Ref. #319433-047 Chapter 12 [2]: https://www.intel.com/content/www/us/en/developer/articles/technical/softwar...
Chao Gao (3): KVM: VMX: Advertise MITI_ENUM_RETPOLINE_S_SUPPORT KVM: selftests: Add tests for virtual enumeration/mitigation MSRs KVM: selftests: Add tests for IA32_SPEC_CTRL MSR
Pawan Gupta (1): x86/bugs: Use Virtual MSRs to request hardware mitigations
Zhang Chen (7): x86/msr-index: Add bit definitions for BHI_DIS_S and BHI_NO KVM: x86: Advertise CPUID.7.2.EDX and RRSBA_CTRL support KVM: x86: Advertise BHI_CTRL support KVM: VMX: Add IA32_SPEC_CTRL virtualization support KVM: x86: Advertise ARCH_CAP_VIRTUAL_ENUM support KVM: VMX: Advertise MITIGATION_CTRL support KVM: VMX: Advertise MITI_CTRL_BHB_CLEAR_SEQ_S_SUPPORT
arch/x86/include/asm/msr-index.h | 33 +++- arch/x86/include/asm/vmx.h | 5 + arch/x86/include/asm/vmxfeatures.h | 2 + arch/x86/kernel/cpu/bugs.c | 25 +++ arch/x86/kvm/cpuid.c | 22 ++- arch/x86/kvm/reverse_cpuid.h | 8 + arch/x86/kvm/svm/svm.c | 3 + arch/x86/kvm/vmx/capabilities.h | 5 + arch/x86/kvm/vmx/nested.c | 13 ++ arch/x86/kvm/vmx/vmcs.h | 2 + arch/x86/kvm/vmx/vmx.c | 112 ++++++++++- arch/x86/kvm/vmx/vmx.h | 43 ++++- arch/x86/kvm/x86.c | 19 +- tools/arch/x86/include/asm/msr-index.h | 37 +++- tools/testing/selftests/kvm/Makefile | 2 + .../selftests/kvm/include/x86_64/processor.h | 5 + .../selftests/kvm/x86_64/spec_ctrl_msr_test.c | 178 ++++++++++++++++++ .../kvm/x86_64/virtual_mitigation_msr_test.c | 175 +++++++++++++++++ 18 files changed, 676 insertions(+), 13 deletions(-) create mode 100644 tools/testing/selftests/kvm/x86_64/spec_ctrl_msr_test.c create mode 100644 tools/testing/selftests/kvm/x86_64/virtual_mitigation_msr_test.c
base-commit: 400d2132288edbd6d500f45eab5d85526ca94e46