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a104e0a305
KVM SVM changes for 6.18 - Require a minimum GHCB version of 2 when starting SEV-SNP guests via KVM_SEV_INIT2 so that invalid GHCB versions result in immediate errors instead of latent guest failures. - Add support for Secure TSC for SEV-SNP guests, which prevents the untrusted host from tampering with the guest's TSC frequency, while still allowing the the VMM to configure the guest's TSC frequency prior to launch. - Mitigate the potential for TOCTOU bugs when accessing GHCB fields by wrapping all accesses via READ_ONCE(). - Validate the XCR0 provided by the guest (via the GHCB) to avoid tracking a bogous XCR0 value in KVM's software model. - Save an SEV guest's policy if and only if LAUNCH_START fully succeeds to avoid leaving behind stale state (thankfully not consumed in KVM). - Explicitly reject non-positive effective lengths during SNP's LAUNCH_UPDATE instead of subtly relying on guest_memfd to do the "heavy" lifting. - Reload the pre-VMRUN TSC_AUX on #VMEXIT for SEV-ES guests, not the host's desired TSC_AUX, to fix a bug where KVM could clobber a different vCPU's TSC_AUX due to hardware not matching the value cached in the user-return MSR infrastructure. - Enable AVIC by default for Zen4+ if x2AVIC (and other prereqs) is supported, and clean up the AVIC initialization code along the way.