On 7/30/2024 10:22 AM, Manali Shukla wrote: > On 7/9/2024 11:21 PM, Manali Shukla wrote: >> Malicious guests can cause bus locks to degrade the performance of a >> system. Non-WB (write-back) and misaligned locked RMW >> (read-modify-write) instructions are referred to as "bus locks" and >> require system wide synchronization among all processors to guarantee >> the atomicity. The bus locks can impose notable performance penalties >> for all processors within the system. >> >> Support for the Bus Lock Threshold is indicated by CPUID >> Fn8000_000A_EDX[29] BusLockThreshold=1, the VMCB provides a Bus Lock >> Threshold enable bit and an unsigned 16-bit Bus Lock Threshold count. >> >> VMCB intercept bit >> VMCB Offset Bits Function >> 14h 5 Intercept bus lock operations >> >> Bus lock threshold count >> VMCB Offset Bits Function >> 120h 15:0 Bus lock counter >> >> During VMRUN, the bus lock threshold count is fetched and stored in an >> internal count register. Prior to executing a bus lock within the >> guest, the processor verifies the count in the bus lock register. If >> the count is greater than zero, the processor executes the bus lock, >> reducing the count. However, if the count is zero, the bus lock >> operation is not performed, and instead, a Bus Lock Threshold #VMEXIT >> is triggered to transfer control to the Virtual Machine Monitor (VMM). >> >> A Bus Lock Threshold #VMEXIT is reported to the VMM with VMEXIT code >> 0xA5h, VMEXIT_BUSLOCK. EXITINFO1 and EXITINFO2 are set to 0 on >> a VMEXIT_BUSLOCK. On a #VMEXIT, the processor writes the current >> value of the Bus Lock Threshold Counter to the VMCB. >> >> More details about the Bus Lock Threshold feature can be found in AMD >> APM [1]. >> >> Patches are prepared on kvm-x86/svm (704ec48fc2fb) >> >> Testing done: >> - Added a selftest for the Bus Lock Threadshold functionality. >> - Tested the Bus Lock Threshold functionality on SEV and SEV-ES guests. >> - Tested the Bus Lock Threshold functionality on nested guests. >> >> Qemu changes can be found on: >> Repo: https://github.com/AMDESE/qemu.git >> Branch: buslock_threshold >> >> Qemu commandline to use the bus lock threshold functionality: >> qemu-system-x86_64 -enable-kvm -cpu EPYC-Turin,+svm -M q35,bus-lock-ratelimit=10 \ .. >> >> [1]: AMD64 Architecture Programmer's Manual Pub. 24593, April 2024, >> Vol 2, 15.14.5 Bus Lock Threshold. >> https://bugzilla.kernel.org/attachment.cgi?id=306250 >> >> Manali Shukla (2): >> x86/cpufeatures: Add CPUID feature bit for the Bus Lock Threshold >> KVM: x86: nSVM: Implement support for nested Bus Lock Threshold >> >> Nikunj A Dadhania (2): >> KVM: SVM: Enable Bus lock threshold exit >> KVM: selftests: Add bus lock exit test >> >> arch/x86/include/asm/cpufeatures.h | 1 + >> arch/x86/include/asm/svm.h | 5 +- >> arch/x86/include/uapi/asm/svm.h | 2 + >> arch/x86/kvm/governed_features.h | 1 + >> arch/x86/kvm/svm/nested.c | 25 ++++ >> arch/x86/kvm/svm/svm.c | 48 ++++++++ >> arch/x86/kvm/svm/svm.h | 1 + >> arch/x86/kvm/x86.h | 1 + >> tools/testing/selftests/kvm/Makefile | 1 + >> .../selftests/kvm/x86_64/svm_buslock_test.c | 114 ++++++++++++++++++ >> 10 files changed, 198 insertions(+), 1 deletion(-) >> create mode 100644 tools/testing/selftests/kvm/x86_64/svm_buslock_test.c >> >> >> base-commit: 704ec48fc2fbd4e41ec982662ad5bf1eee33eeb2 > > A gentle reminder. > > -Manali A gentle reminder. - Manali
