[PATCH RFC v8 48/56] KVM: SVM: Add SNP-specific handling for memory attribute updates

[Michael Roth]

This will handle RMP table updates and direct map changes needed for
page state conversions requested by userspace.

Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
 arch/x86/kvm/svm/sev.c | 126 +++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.c |   1 +
 arch/x86/kvm/svm/svm.h |   2 +
 3 files changed, 129 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index b2f1a12685ed..73d614c538da 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3381,6 +3381,31 @@ static int snp_rmptable_psmash(struct kvm *kvm, kvm_pfn_t pfn)
 	return psmash(pfn);
 }
 
+static int snp_make_page_shared(struct kvm *kvm, gpa_t gpa, kvm_pfn_t pfn, int level)
+{
+	int rc, rmp_level;
+
+	rc = snp_lookup_rmpentry(pfn, &rmp_level);
+	if (rc < 0)
+		return -EINVAL;
+
+	/* If page is not assigned then do nothing */
+	if (!rc)
+		return 0;
+
+	/*
+	 * Is the page part of an existing 2MB RMP entry ? Split the 2MB into
+	 * multiple of 4K-page before making the memory shared.
+	 */
+	if (level == PG_LEVEL_4K && rmp_level == PG_LEVEL_2M) {
+		rc = snp_rmptable_psmash(kvm, pfn);
+		if (rc)
+			return rc;
+	}
+
+	return rmp_make_shared(pfn, level);
+}
+
 /*
  * TODO: need to get the value set by userspace in vcpu->run->vmgexit.ghcb_msr
  * and process that here accordingly.
@@ -4373,3 +4398,104 @@ void handle_rmp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code)
 	kvm_zap_gfn_range(kvm, gfn, gfn + PTRS_PER_PMD);
 	put_page(pfn_to_page(pfn));
 }
+
+static inline u8 order_to_level(int order)
+{
+	BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
+
+	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
+		return PG_LEVEL_1G;
+
+	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
+		return PG_LEVEL_2M;
+
+	return PG_LEVEL_4K;
+}
+
+int sev_update_mem_attr(struct kvm_memory_slot *slot, unsigned int attr,
+			gfn_t start, gfn_t end)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(slot->kvm)->sev_info;
+	enum psc_op op = (attr & KVM_MEMORY_ATTRIBUTE_PRIVATE) ? SNP_PAGE_STATE_PRIVATE
+							       : SNP_PAGE_STATE_SHARED;
+	gfn_t gfn = start;
+
+	pr_debug("%s: GFN 0x%llx - 0x%llx, op: %d\n", __func__, start, end, op);
+
+	if (!sev_snp_guest(slot->kvm))
+		return 0;
+
+	if (!kvm_slot_can_be_private(slot)) {
+		pr_err_ratelimited("%s: memslot for gfn: 0x%llx is not private.\n",
+				   __func__, gfn);
+		return -EPERM;
+	}
+
+	while (gfn < end) {
+		kvm_pfn_t pfn;
+		int level = PG_LEVEL_4K; /* TODO: take actual order into account */
+		gpa_t gpa = gfn_to_gpa(gfn);
+		int npages = 1;
+		int order;
+		int rc;
+
+		/*
+		 * No work to do if there was never a page allocated from private
+		 * memory. If there was a page that was deallocated previously,
+		 * the invalidation notifier should have restored the page to
+		 * shared.
+		 */
+		rc = kvm_restrictedmem_get_pfn(slot, gfn, &pfn, &order);
+		if (rc) {
+			pr_warn_ratelimited("%s: failed to retrieve gfn 0x%llx from private FD\n",
+					    __func__, gfn);
+			gfn++;
+			continue;
+		}
+
+		/*
+		 * TODO: The RMP entry's hugepage bit is ignored for
+		 * shared/unassigned pages. Either handle looping through each
+		 * sub-page as part of snp_make_page_shared(), or remove the
+		 * level argument.
+		 */
+		if (op == SNP_PAGE_STATE_PRIVATE && order &&
+		    IS_ALIGNED(gfn, 1 << order) && (gfn + (1 << order)) <= end) {
+			level = order_to_level(order);
+			npages = 1 << order;
+		}
+
+		/*
+		 * Grab the PFN from private memslot and update the RMP entry.
+		 * It may be worthwhile to go ahead and map it into the TDP at
+		 * this point if the guest is doing lazy acceptance, but for
+		 * up-front bulk shared->private conversions it's not likely
+		 * the guest will try to access the PFN any time soon, so for
+		 * now just take the let KVM MMU handle faulting it on the next
+		 * access.
+		 */
+		switch (op) {
+		case SNP_PAGE_STATE_SHARED:
+			rc = snp_make_page_shared(slot->kvm, gpa, pfn, level);
+			break;
+		case SNP_PAGE_STATE_PRIVATE:
+			rc = rmp_make_private(pfn, gpa, level, sev->asid, false);
+			break;
+		default:
+			rc = PSC_INVALID_ENTRY;
+			break;
+		}
+
+		put_page(pfn_to_page(pfn));
+
+		if (rc) {
+			pr_err_ratelimited("%s: failed op %d gpa %llx pfn %llx level %d rc %d\n",
+					   __func__, op, gpa, pfn, level, rc);
+			return -EINVAL;
+		}
+
+		gfn += npages;
+	}
+
+	return 0;
+}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 539926b07ee5..e2edc4700e55 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4860,6 +4860,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 	.alloc_apic_backing_page = svm_alloc_apic_backing_page,
 
 	.adjust_mapping_level = sev_adjust_mapping_level,
+	.update_mem_attr = sev_update_mem_attr,
 };
 
 /*
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 37bd7b728d52..50a2bcaf3fd7 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -725,6 +725,8 @@ struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu);
 void sev_adjust_mapping_level(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int *level);
 void handle_rmp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code);
 void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu);
+int sev_update_mem_attr(struct kvm_memory_slot *slot, unsigned int attr,
+			gfn_t start, gfn_t end);
 
 /* vmenter.S */
 
-- 
2.25.1