Merge tag 'kvm-x86-svm-6.18' of https://github.com/kvm-x86/linux into HEAD

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.

virt/kvm/guest_memfd.c

@@ -716,7 +716,8 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long
 	long i;
 
 	lockdep_assert_held(&kvm->slots_lock);
-	if (npages < 0)
+
+	if (WARN_ON_ONCE(npages <= 0))
 		return -EINVAL;
 
 	slot = gfn_to_memslot(kvm, start_gfn);