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    SubjectRe: [PATCH Part2 v6 37/49] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT
    > +
    > +static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op, gpa_t gpa,
    > + int level)
    > +{
    > + struct kvm_sev_info *sev = &to_kvm_svm(vcpu->kvm)->sev_info;
    > + struct kvm *kvm = vcpu->kvm;
    > + int rc, npt_level;
    > + kvm_pfn_t pfn;
    > + gpa_t gpa_end;
    > +
    > + gpa_end = gpa + page_level_size(level);
    > +
    > + while (gpa < gpa_end) {
    > + /*
    > + * If the gpa is not present in the NPT then build the NPT.
    > + */
    > + rc = snp_check_and_build_npt(vcpu, gpa, level);
    > + if (rc)
    > + return -EINVAL;
    > +
    > + if (op == SNP_PAGE_STATE_PRIVATE) {
    > + hva_t hva;
    > +
    > + if (snp_gpa_to_hva(kvm, gpa, &hva))
    > + return -EINVAL;
    > +
    > + /*
    > + * Verify that the hva range is registered. This enforcement is
    > + * required to avoid the cases where a page is marked private
    > + * in the RMP table but never gets cleanup during the VM
    > + * termination path.
    > + */
    > + mutex_lock(&kvm->lock);
    > + rc = is_hva_registered(kvm, hva, page_level_size(level));
    > + mutex_unlock(&kvm->lock);
    > + if (!rc)
    > + return -EINVAL;
    > +
    > + /*
    > + * Mark the userspace range unmerable before adding the pages
    > + * in the RMP table.
    > + */
    > + mmap_write_lock(kvm->mm);
    > + rc = snp_mark_unmergable(kvm, hva, page_level_size(level));
    > + mmap_write_unlock(kvm->mm);
    > + if (rc)
    > + return -EINVAL;
    > + }
    > +
    > + write_lock(&kvm->mmu_lock);
    > +
    > + rc = kvm_mmu_get_tdp_walk(vcpu, gpa, &pfn, &npt_level);
    > + if (!rc) {
    > + /*
    > + * This may happen if another vCPU unmapped the page
    > + * before we acquire the lock. Retry the PSC.
    > + */
    > + write_unlock(&kvm->mmu_lock);
    > + return 0;
    > + }

    I think we want to return -EAGAIN or similar if we want the caller to
    retry, right? I think returning 0 here hides the error.

    > +
    > + /*
    > + * Adjust the level so that we don't go higher than the backing
    > + * page level.
    > + */
    > + level = min_t(size_t, level, npt_level);
    > +
    > + trace_kvm_snp_psc(vcpu->vcpu_id, pfn, gpa, op, level);
    > +
    > + switch (op) {
    > + case SNP_PAGE_STATE_SHARED:
    > + rc = snp_make_page_shared(kvm, gpa, pfn, level);
    > + break;
    > + case SNP_PAGE_STATE_PRIVATE:
    > + rc = rmp_make_private(pfn, gpa, level, sev->asid, false);
    > + break;
    > + default:
    > + rc = -EINVAL;
    > + break;
    > + }
    > +
    > + write_unlock(&kvm->mmu_lock);
    > +
    > + if (rc) {
    > + pr_err_ratelimited("Error op %d gpa %llx pfn %llx level %d rc %d\n",
    > + op, gpa, pfn, level, rc);
    > + return rc;
    > + }
    > +
    > + gpa = gpa + page_level_size(level);
    > + }
    > +
    > + return 0;
    > +}
    > +

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