Svsm planes+SecureTSC #18
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Remove the GHCB_VERSION_DEFAULT macro and open code it with '2'. The macro is used conditionally and is not a true default. KVM ABI does not advertise/emumerates the default GHCB version. Any future change to this macro would silently alter the ABI and potentially break existing deployments that rely on the current behavior. Additionally, move the GHCB version assignment earlier in the code flow and update the comment to clarify that KVM_SEV_INIT2 defaults to version 2, while KVM_SEV_INIT forces version 1. No functional change intended. Cc: Thomas Lendacky <thomas.lendacky@amd.com> Cc: Michael Roth <michael.roth@amd.com> Suggested-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com> Link: https://lore.kernel.org/r/20250819234833.3080255-2-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Require a minimum GHCB version of 2 when starting SEV-SNP guests through KVM_SEV_INIT2. When a VMM attempts to start an SEV-SNP guest with an incompatible GHCB version (less than 2), reject the request early rather than allowing the guest kernel to start with an incorrect protocol version and fail later with GHCB_SNP_UNSUPPORTED guest termination. Not enforcing the minimum version typically causes the guest to request termination with GHCB_SNP_UNSUPPORTED error code: kvm_amd: SEV-ES guest requested termination: 0x0:0x2 Fixes: 4af663c ("KVM: SEV: Allow per-guest configuration of GHCB protocol version") Cc: Thomas Lendacky <thomas.lendacky@amd.com> Cc: Sean Christopherson <seanjc@google.com> Cc: Michael Roth <michael.roth@amd.com> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com> Link: https://lore.kernel.org/r/20250819234833.3080255-3-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
The Secure TSC feature for SEV-SNP allows guests to securely use the RDTSC and RDTSCP instructions, ensuring that the parameters used cannot be altered by the hypervisor once the guest is launched. For more details, refer to the AMD64 APM Vol 2, Section "Secure TSC". Acked-by: Borislav Petkov (AMD) <bp@alien8.de> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> Tested-by: Vaishali Thakkar <vaishali.thakkar@suse.com> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com> Link: https://lore.kernel.org/r/20250819234833.3080255-4-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
…) helper Add a dedicated sev_vcpu_create() helper to allocate the VMSA page for SEV-ES+ vCPUs, and to allow for consolidating a variety of related SEV+ code in the near future. No functional change intended. (vaishali: Resolve merge conflicts) Reviewed-by: Nikunj A Dadhania <nikunj@amd.com> Link: https://lore.kernel.org/r/20250819234833.3080255-5-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Move the initialization of SNP guest state from svm_vcpu_reset() into sev_init_vmcb() to reduce the number of paths that deal with INIT/RESET for SEV+ vCPUs from 4+ to 1. Plumb in @init_event as necessary. Opportunistically check for an SNP guest outside of sev_snp_init_protected_guest_state() so that sev_init_vmcb() is consistent with respect to checking for SEV-ES+ and SNP+ guests. No functional change intended. Reviewed-by: Nikunj A Dadhania <nikunj@amd.com> Link: https://lore.kernel.org/r/20250819234833.3080255-6-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Set the RESET value for the GHCB "MSR" during sev_es_init_vmcb() instead of sev_es_vcpu_reset() to allow for dropping sev_es_vcpu_reset() entirely. Note, the call to sev_init_vmcb() from sev_migrate_from() also kinda sorta emulates a RESET, but sev_migrate_from() immediately overwrites ghcb_gpa with the source's current value, so whether or not stuffing the GHCB version is correct/desirable is moot. No functional change intended. (vaishali: Bring back 'sev' variable which was removed as part of the commit e07c01e) Reviewed-by: Nikunj A Dadhania <nikunj@amd.com> Link: https://lore.kernel.org/r/20250819234833.3080255-7-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Fold the remaining line of sev_es_vcpu_reset() into sev_vcpu_create() as there's no need for a dedicated RESET hook just to init a mutex, and the mutex should be initialized as early as possible anyways. No functional change intended. Reviewed-by: Nikunj A Dadhania <nikunj@amd.com> Link: https://lore.kernel.org/r/20250819234833.3080255-8-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Add support for Secure TSC, allowing userspace to configure the Secure TSC feature for SNP guests. Use the SNP specification's desired TSC frequency parameter during the SNP_LAUNCH_START command to set the mean TSC frequency in KHz for Secure TSC enabled guests. Always use kvm->arch.arch.default_tsc_khz as the TSC frequency that is passed to SNP guests in the SNP_LAUNCH_START command. The default value is the host TSC frequency. The userspace can optionally change the TSC frequency via the KVM_SET_TSC_KHZ ioctl before calling the SNP_LAUNCH_START ioctl. Introduce the read-only MSR GUEST_TSC_FREQ (0xc0010134) that returns guest's effective frequency in MHZ when Secure TSC is enabled for SNP guests. Disable interception of this MSR when Secure TSC is enabled. Note that GUEST_TSC_FREQ MSR is accessible only to the guest and not from the hypervisor context. Co-developed-by: Ketan Chaturvedi <Ketan.Chaturvedi@amd.com> Signed-off-by: Ketan Chaturvedi <Ketan.Chaturvedi@amd.com> Reviewed-by: Kai Huang <kai.huang@intel.com> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com> [sean: contain Secure TSC to sev.c] Link: https://lore.kernel.org/r/20250819234833.3080255-9-seanjc@google.com [sean: return -EINVAL if TSC frequency is '0'] Signed-off-by: Sean Christopherson <seanjc@google.com>
This was referenced Nov 5, 2025
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Hi @v-thakkar, thanks for your work! Quick question t ocalify some high-level understanding: These changes here are for the host or the guest kernel? Do they work independently of the QEMU changes in coconut-svsm/qemu#26, or do need both? |
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Hi @osteffenrh, it's for the host kernel. Guest kernel patches were merged in the earlier kernel(6.16 I think). So they're already there in the svsm-plane-v6.17 branch. The QEMU changes are independent of these changes for now. But I think they'll be needed when we have SecureTSC support in coconut-svsm. Mainly because of this patch which makes sure to only set SEV features through qemu cmdline or IGVM. |
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This PR has 8 cherry-picked commits from the merged series that enables SecureTSC in upstream Linux host kernel. Corresponding qemu PR can be found here.