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[v2,0/4] Enable Secure TSC for SEV-SNP

Message ID 20250210092230.151034-1-nikunj@amd.com (mailing list archive)
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Series Enable Secure TSC for SEV-SNP | expand

Message

Nikunj A Dadhania Feb. 10, 2025, 9:22 a.m. UTC 
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 patchset is also available at:

  https://github.com/AMDESE/linux-kvm/tree/sectsc-host-latest

and is based on kvm/next

Testing SecureTSC
-----------------

SecureTSC guest patches are available as part of v6.14-rc1.

QEMU changes:
https://github.com/nikunjad/qemu/tree/snp-securetsc-latest

QEMU commandline SEV-SNP with SecureTSC:

  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:
----------
v2:
* Address cpufeatures comment from Boris
* Squashed Secure TSC enablement and setting frequency patch
* Set the default TSC KHz for proper calulation of guest offset/multiplier

Ketan Chaturvedi (1):
  KVM: SVM: Enable Secure TSC for SNP guests

Nikunj A Dadhania (3):
  x86/cpufeatures: Add SNP Secure TSC
  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             | 12 ++++++++++++
 arch/x86/kvm/svm/svm.h             | 14 +++++++++++++-
 include/linux/psp-sev.h            |  2 ++
 7 files changed, 53 insertions(+), 2 deletions(-)


base-commit: 43fb96ae78551d7bfa4ecca956b258f085d67c40