The hypervisor controls TSC value calculations for the guest. A malicious hypervisor can prevent the guest from progressing. The Secure TSC feature for SEV-SNP allows guests to securely use the RDTSC and RDTSCP instructions. This ensures the guest has a consistent view of time and prevents a malicious hypervisor from manipulating time, such as making it appear to move backward or advance too quickly. For more details, refer to the "Secure Nested Paging (SEV-SNP)" section, subsection "Secure TSC" in APM Volume 2. This patch set is also available at: https://github.com/AMDESE/linux-kvm/tree/sectsc-host-latest and is based on kvm-x86/next Testing Secure TSC ----------------- Secure TSC guest patches are available as part of v6.14-rc1. QEMU changes: https://github.com/nikunjad/qemu/tree/snp-securetsc-latest QEMU command line SEV-SNP with Secure TSC: qemu-system-x86_64 -cpu EPYC-Milan-v2 -smp 4 \ -object memory-backend-memfd,id=ram1,size=1G,share=true,prealloc=false,reserve=false \ -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1,secure-tsc=on,stsc-freq=2000000000 \ -machine q35,confidential-guest-support=sev0,memory-backend=ram1 \ ... Changelog: ---------- v3: * Rebased on top of kvm-x86/next * Collect Acked-by * Separate patch to add missing desired_tsc_khz field (Tom) * Invoke kvm_set_msr_common() for non-SecureTSC guests (Tom) * To align desired_tsc_khz to 4-byte boundary, move the 2-byte pad0 above it (Tom) * Update commit logs (Tom, Sean) v2: https://lore.kernel.org/all/20250210092230.151034-1-nikunj@xxxxxxx/ * Address cpufeatures comment from Boris * Squashed Secure TSC enablement and setting frequency patch * Set the default TSC KHz for proper calculation of guest offset/multiplier Ketan Chaturvedi (1): KVM: SVM: Enable Secure TSC for SNP guests Nikunj A Dadhania (4): x86/cpufeatures: Add SNP Secure TSC crypto: ccp: Add missing member in SNP_LAUNCH_START command structure KVM: SVM: Add GUEST_TSC_FREQ MSR for Secure TSC enabled guests KVM: SVM: Prevent writes to TSC MSR when Secure TSC is enabled arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/svm.h | 1 + arch/x86/include/uapi/asm/kvm.h | 3 ++- arch/x86/kvm/svm/sev.c | 22 ++++++++++++++++++++++ arch/x86/kvm/svm/svm.c | 15 +++++++++++++++ arch/x86/kvm/svm/svm.h | 11 ++++++++++- include/linux/psp-sev.h | 2 ++ 7 files changed, 53 insertions(+), 2 deletions(-) base-commit: fed48e2967f402f561d80075a20c5c9e16866e53 -- 2.43.0
