Re: [PATCH Part2 v6 37/49] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT

Peter Gonda
2022-08-19T17:36:55Z

> +
> +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;
> +}
> +