This patch set enables the Intel flexible return and event delivery (FRED) architecture with KVM VMX to allow guests to utilize FRED.
The FRED architecture defines simple new transitions that change privilege level (ring transitions). The FRED architecture was designed with the following goals:
1) Improve overall performance and response time by replacing event delivery through the interrupt descriptor table (IDT event delivery) and event return by the IRET instruction with lower latency transitions.
2) Improve software robustness by ensuring that event delivery establishes the full supervisor context and that event return establishes the full user context.
The new transitions defined by the FRED architecture are FRED event delivery and, for returning from events, two FRED return instructions. FRED event delivery can effect a transition from ring 3 to ring 0, but it is used also to deliver events incident to ring 0. One FRED instruction (ERETU) effects a return from ring 0 to ring 3, while the other (ERETS) returns while remaining in ring 0. Collectively, FRED event delivery and the FRED return instructions are FRED transitions.
Intel VMX architecture is extended to run FRED guests, and the major changes are:
1) New VMCS fields for FRED context management, which includes two new event data VMCS fields, eight new guest FRED context VMCS fields and eight new host FRED context VMCS fields.
2) VMX nested-exception support for proper virtualization of stack levels introduced with FRED architecture.
Search for the latest FRED spec in most search engines with this search pattern:
site:intel.com FRED (flexible return and event delivery) specification
As the native FRED patches are committed in the tip tree "x86/fred" branch: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=x86/fred, and we have received a good amount of review comments for v1, it's time to send out v2 based on this branch for further help from the community.
Patch 1-2 are cleanups to VMX basic and misc MSRs, which were sent out earlier as a preparation for FRED changes: https://lore.kernel.org/kvm/20240206182032.1596-1-xin3.li@intel.com/T/#u
Patch 3-15 add FRED support to VMX. Patch 16-21 add FRED support to nested VMX. Patch 22 exposes FRED and its baseline features to KVM guests. Patch 23-25 add FRED selftests.
There is also a counterpart qemu patch set for FRED at: https://lore.kernel.org/qemu-devel/20231109072012.8078-1-xin3.li@intel.com/T..., which works with this patch set to allow KVM to run FRED guests.
Changes since v1: * Always load the secondary VM exit controls (Sean Christopherson). * Remove FRED VM entry/exit controls consistency checks in setup_vmcs_config() (Sean Christopherson). * Clear FRED VM entry/exit controls if FRED is not enumerated (Chao Gao). * Use guest_can_use() to trace FRED enumeration in a vcpu (Chao Gao). * Enable FRED MSRs intercept if FRED is no longer enumerated in CPUID (Chao Gao). * Move guest FRED states init into __vmx_vcpu_reset() (Chao Gao). * Don't use guest_cpuid_has() in vmx_prepare_switch_to_{host,guest}(), which are called from IRQ-disabled context (Chao Gao). * Reset msr_guest_fred_rsp0 in __vmx_vcpu_reset() (Chao Gao). * Fail host requested FRED MSRs access if KVM cannot virtualize FRED (Chao Gao). * Handle the case FRED MSRs are valid but KVM cannot virtualize FRED (Chao Gao). * Add sanity checks when writing to FRED MSRs. * Explain why it is ok to only check CR4.FRED in kvm_is_fred_enabled() (Chao Gao). * Document event data should be equal to CR2/DR6/IA32_XFD_ERR instead of using WARN_ON() (Chao Gao). * Zero event data if a #NM was not caused by extended feature disable (Chao Gao). * Set the nested flag when there is an original interrupt (Chao Gao). * Dump guest FRED states only if guest has FRED enabled (Nikolay Borisov). * Add a prerequisite to SHADOW_FIELD_R[OW] macros * Remove hyperv TLFS related changes (Jeremi Piotrowski). * Use kvm_cpu_cap_has() instead of cpu_feature_enabled() to decouple KVM's capability to virtualize a feature and host's enabling of a feature (Chao Gao).
Xin Li (25): KVM: VMX: Cleanup VMX basic information defines and usages KVM: VMX: Cleanup VMX misc information defines and usages KVM: VMX: Add support for the secondary VM exit controls KVM: x86: Mark CR4.FRED as not reserved KVM: VMX: Initialize FRED VM entry/exit controls in vmcs_config KVM: VMX: Defer enabling FRED MSRs save/load until after set CPUID KVM: VMX: Set intercept for FRED MSRs KVM: VMX: Initialize VMCS FRED fields KVM: VMX: Switch FRED RSP0 between host and guest KVM: VMX: Add support for FRED context save/restore KVM: x86: Add kvm_is_fred_enabled() KVM: VMX: Handle FRED event data KVM: VMX: Handle VMX nested exception for FRED KVM: VMX: Disable FRED if FRED consistency checks fail KVM: VMX: Dump FRED context in dump_vmcs() KVM: VMX: Invoke vmx_set_cpu_caps() before nested setup KVM: nVMX: Add support for the secondary VM exit controls KVM: nVMX: Add a prerequisite to SHADOW_FIELD_R[OW] macros KVM: nVMX: Add FRED VMCS fields KVM: nVMX: Add support for VMX FRED controls KVM: nVMX: Add VMCS FRED states checking KVM: x86: Allow FRED/LKGS/WRMSRNS to be exposed to guests KVM: selftests: Run debug_regs test with FRED enabled KVM: selftests: Add a new VM guest mode to run user level code KVM: selftests: Add fred exception tests
Documentation/virt/kvm/x86/nested-vmx.rst | 19 + arch/x86/include/asm/kvm_host.h | 8 +- arch/x86/include/asm/msr-index.h | 15 +- arch/x86/include/asm/vmx.h | 59 ++- arch/x86/kvm/cpuid.c | 4 +- arch/x86/kvm/governed_features.h | 1 + arch/x86/kvm/kvm_cache_regs.h | 17 + arch/x86/kvm/svm/svm.c | 4 +- arch/x86/kvm/vmx/capabilities.h | 30 +- arch/x86/kvm/vmx/nested.c | 329 ++++++++++++--- arch/x86/kvm/vmx/nested.h | 2 +- arch/x86/kvm/vmx/vmcs.h | 1 + arch/x86/kvm/vmx/vmcs12.c | 19 + arch/x86/kvm/vmx/vmcs12.h | 38 ++ arch/x86/kvm/vmx/vmcs_shadow_fields.h | 80 ++-- arch/x86/kvm/vmx/vmx.c | 385 +++++++++++++++--- arch/x86/kvm/vmx/vmx.h | 15 +- arch/x86/kvm/x86.c | 103 ++++- arch/x86/kvm/x86.h | 5 +- tools/testing/selftests/kvm/Makefile | 1 + .../selftests/kvm/include/kvm_util_base.h | 1 + .../selftests/kvm/include/x86_64/processor.h | 36 ++ tools/testing/selftests/kvm/lib/kvm_util.c | 5 +- .../selftests/kvm/lib/x86_64/processor.c | 15 +- tools/testing/selftests/kvm/lib/x86_64/vmx.c | 4 +- .../testing/selftests/kvm/x86_64/debug_regs.c | 50 ++- .../testing/selftests/kvm/x86_64/fred_test.c | 297 ++++++++++++++ 27 files changed, 1320 insertions(+), 223 deletions(-) create mode 100644 tools/testing/selftests/kvm/x86_64/fred_test.c
base-commit: e13841907b8fda0ae0ce1ec03684665f578416a8