[PATCH v11 28/35] KVM: SEV: Implement gmem hook for initializing private pages

[Michael Roth <michael.roth@amd.com>]

This will handle RMP table updates and direct map changes needed to put
a page into a private state before mapping it into an SEV-SNP guest.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 arch/x86/kvm/Kconfig   |  1 +
 arch/x86/kvm/svm/sev.c | 98 ++++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.c |  2 +
 arch/x86/kvm/svm/svm.h |  1 +
 virt/kvm/guest_memfd.c |  4 +-
 5 files changed, 104 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 4ec53d6d5773..79c002e1bb5c 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -125,6 +125,7 @@ config KVM_AMD_SEV
 	depends on KVM_AMD && X86_64
 	depends on CRYPTO_DEV_SP_PSP && !(KVM_AMD=y && CRYPTO_DEV_CCP_DD=m)
 	select KVM_GENERIC_PRIVATE_MEM
+	select HAVE_KVM_GMEM_PREPARE
 	help
 	  Provides support for launching Encrypted VMs (SEV) and Encrypted VMs
 	  with Encrypted State (SEV-ES) on AMD processors.
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index b2ac696c436a..91f53f4a6059 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -4154,3 +4154,101 @@ void handle_rmp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code)
 out:
 	put_page(pfn_to_page(pfn));
 }
+
+static bool is_pfn_range_shared(kvm_pfn_t start, kvm_pfn_t end)
+{
+	kvm_pfn_t pfn = start;
+
+	while (pfn < end) {
+		int ret, rmp_level;
+		bool assigned;
+
+		ret = snp_lookup_rmpentry(pfn, &assigned, &rmp_level);
+		if (ret) {
+			pr_warn_ratelimited("SEV: Failed to retrieve RMP entry: PFN 0x%llx GFN start 0x%llx GFN end 0x%llx RMP level %d error %d\n",
+					    pfn, start, end, rmp_level, ret);
+			return false;
+		}
+
+		if (assigned) {
+			pr_debug("%s: overlap detected, PFN 0x%llx start 0x%llx end 0x%llx RMP level %d\n",
+				 __func__, pfn, start, end, rmp_level);
+			return false;
+		}
+
+		pfn++;
+	}
+
+	return true;
+}
+
+static u8 max_level_for_order(int order)
+{
+	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
+		return PG_LEVEL_2M;
+
+	return PG_LEVEL_4K;
+}
+
+static bool is_large_rmp_possible(struct kvm *kvm, kvm_pfn_t pfn, int order)
+{
+	kvm_pfn_t pfn_aligned = ALIGN_DOWN(pfn, PTRS_PER_PMD);
+
+	/*
+	 * If this is a large folio, and the entire 2M range containing the
+	 * PFN is currently shared, then the entire 2M-aligned range can be
+	 * set to private via a single 2M RMP entry.
+	 */
+	if (max_level_for_order(order) > PG_LEVEL_4K &&
+	    is_pfn_range_shared(pfn_aligned, pfn_aligned + PTRS_PER_PMD))
+		return true;
+
+	return false;
+}
+
+int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	kvm_pfn_t pfn_aligned;
+	gfn_t gfn_aligned;
+	int level, rc;
+	bool assigned;
+
+	if (!sev_snp_guest(kvm))
+		return 0;
+
+	rc = snp_lookup_rmpentry(pfn, &assigned, &level);
+	if (rc) {
+		pr_err_ratelimited("SEV: Failed to look up RMP entry: GFN %llx PFN %llx error %d\n",
+				   gfn, pfn, rc);
+		return -ENOENT;
+	}
+
+	if (assigned) {
+		pr_debug("%s: already assigned: gfn %llx pfn %llx max_order %d level %d\n",
+			 __func__, gfn, pfn, max_order, level);
+		return 0;
+	}
+
+	if (is_large_rmp_possible(kvm, pfn, max_order)) {
+		level = PG_LEVEL_2M;
+		pfn_aligned = ALIGN_DOWN(pfn, PTRS_PER_PMD);
+		gfn_aligned = ALIGN_DOWN(gfn, PTRS_PER_PMD);
+	} else {
+		level = PG_LEVEL_4K;
+		pfn_aligned = pfn;
+		gfn_aligned = gfn;
+	}
+
+	rc = rmp_make_private(pfn_aligned, gfn_to_gpa(gfn_aligned), level, sev->asid, false);
+	if (rc) {
+		pr_err_ratelimited("SEV: Failed to update RMP entry: GFN %llx PFN %llx level %d error %d\n",
+				   gfn, pfn, level, rc);
+		return -EINVAL;
+	}
+
+	pr_debug("%s: updated: gfn %llx pfn %llx pfn_aligned %llx max_order %d level %d\n",
+		 __func__, gfn, pfn, pfn_aligned, max_order, level);
+
+	return 0;
+}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 240518f8d6c7..32cef8626b57 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5065,6 +5065,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 	.vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector,
 	.vcpu_get_apicv_inhibit_reasons = avic_vcpu_get_apicv_inhibit_reasons,
 	.alloc_apic_backing_page = svm_alloc_apic_backing_page,
+
+	.gmem_prepare = sev_gmem_prepare,
 };
 
 /*
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index d953ae41c619..9ece9612dbb9 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -725,6 +725,7 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
 struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu);
 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_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order);
 
 /* vmenter.S */
 
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index feec0da93d98..ddea45279fef 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -66,8 +66,8 @@ static int kvm_gmem_prepare_folio(struct inode *inode, pgoff_t index, struct fol
 		gfn = slot->base_gfn + index - slot->gmem.pgoff;
 		rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, compound_order(compound_head(page)));
 		if (rc) {
-			pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx, error %d.\n",
-					    index, rc);
+			pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx GFN %llx PFN %llx error %d.\n",
+					    index, gfn, pfn, rc);
 			return rc;
 		}
 	}
-- 
2.25.1