[RFC,v7,43/64] KVM: SVM: Do not use long-lived GHCB map while setting scratch area

Commit Message

Michael Roth Dec. 14, 2022, 7:40 p.m. UTC

From: Brijesh Singh <[e-mail]>

The setup_vmgexit_scratch() function may rely on a long-lived GHCB
mapping if the GHCB shared buffer area was used for the scratch area.
In preparation for eliminating the long-lived GHCB mapping, always
allocate a buffer for the scratch area so it can be accessed without
the GHCB mapping.

Signed-off-by: Brijesh Singh <[e-mail]>
Signed-off-by: Ashish Kalra <[e-mail]>
Signed-off-by: Michael Roth <[e-mail]>
---
 arch/x86/kvm/svm/sev.c | 74 +++++++++++++++++++-----------------------
 arch/x86/kvm/svm/svm.h |  3 +-
 2 files changed, 36 insertions(+), 41 deletions(-)

Patch

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 443c5c8aaaf3..d5c6e48055fb 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2918,8 +2918,7 @@  void sev_free_vcpu(struct kvm_vcpu *vcpu)
 	__free_page(virt_to_page(svm->sev_es.vmsa));
 
 skip_vmsa_free:
-	if (svm->sev_es.ghcb_sa_free)
-		kvfree(svm->sev_es.ghcb_sa);
+	kvfree(svm->sev_es.ghcb_sa);
 }
 
 static void dump_ghcb(struct vcpu_svm *svm)
@@ -3007,6 +3006,9 @@  static void sev_es_sync_from_ghcb(struct vcpu_svm *svm)
 	control->exit_info_1 = ghcb_get_sw_exit_info_1(ghcb);
 	control->exit_info_2 = ghcb_get_sw_exit_info_2(ghcb);
 
+	/* Copy the GHCB scratch area GPA */
+	svm->sev_es.ghcb_sa_gpa = ghcb_get_sw_scratch(ghcb);
+
 	/* Clear the valid entries fields */
 	memset(ghcb->save.valid_bitmap, 0, sizeof(ghcb->save.valid_bitmap));
 }
@@ -3152,23 +3154,12 @@  void sev_es_unmap_ghcb(struct vcpu_svm *svm)
 	if (!svm->sev_es.ghcb)
 		return;
 
-	if (svm->sev_es.ghcb_sa_free) {
-		/*
-		 * The scratch area lives outside the GHCB, so there is a
-		 * buffer that, depending on the operation performed, may
-		 * need to be synced, then freed.
-		 */
-		if (svm->sev_es.ghcb_sa_sync) {
-			kvm_write_guest(svm->vcpu.kvm,
-					ghcb_get_sw_scratch(svm->sev_es.ghcb),
-					svm->sev_es.ghcb_sa,
-					svm->sev_es.ghcb_sa_len);
-			svm->sev_es.ghcb_sa_sync = false;
-		}
-
-		kvfree(svm->sev_es.ghcb_sa);
-		svm->sev_es.ghcb_sa = NULL;
-		svm->sev_es.ghcb_sa_free = false;
+	 /* Sync the scratch buffer area. */
+	if (svm->sev_es.ghcb_sa_sync) {
+		kvm_write_guest(svm->vcpu.kvm,
+				ghcb_get_sw_scratch(svm->sev_es.ghcb),
+				svm->sev_es.ghcb_sa, svm->sev_es.ghcb_sa_len);
+		svm->sev_es.ghcb_sa_sync = false;
 	}
 
 	trace_kvm_vmgexit_exit(svm->vcpu.vcpu_id, svm->sev_es.ghcb);
@@ -3209,9 +3200,8 @@  static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
 	struct ghcb *ghcb = svm->sev_es.ghcb;
 	u64 ghcb_scratch_beg, ghcb_scratch_end;
 	u64 scratch_gpa_beg, scratch_gpa_end;
-	void *scratch_va;
 
-	scratch_gpa_beg = ghcb_get_sw_scratch(ghcb);
+	scratch_gpa_beg = svm->sev_es.ghcb_sa_gpa;
 	if (!scratch_gpa_beg) {
 		pr_err("vmgexit: scratch gpa not provided\n");
 		goto e_scratch;
@@ -3241,9 +3231,6 @@  static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
 			       scratch_gpa_beg, scratch_gpa_end);
 			goto e_scratch;
 		}
-
-		scratch_va = (void *)svm->sev_es.ghcb;
-		scratch_va += (scratch_gpa_beg - control->ghcb_gpa);
 	} else {
 		/*
 		 * The guest memory must be read into a kernel buffer, so
@@ -3254,29 +3241,36 @@  static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
 			       len, GHCB_SCRATCH_AREA_LIMIT);
 			goto e_scratch;
 		}
-		scratch_va = kvzalloc(len, GFP_KERNEL_ACCOUNT);
-		if (!scratch_va)
-			return -ENOMEM;
+	}
 
-		if (kvm_read_guest(svm->vcpu.kvm, scratch_gpa_beg, scratch_va, len)) {
-			/* Unable to copy scratch area from guest */
-			pr_err("vmgexit: kvm_read_guest for scratch area failed\n");
+	if (svm->sev_es.ghcb_sa_alloc_len < len) {
+		void *scratch_va = kvzalloc(len, GFP_KERNEL_ACCOUNT);
 
-			kvfree(scratch_va);
-			return -EFAULT;
-		}
+		if (!scratch_va)
+			return -ENOMEM;
 
 		/*
-		 * The scratch area is outside the GHCB. The operation will
-		 * dictate whether the buffer needs to be synced before running
-		 * the vCPU next time (i.e. a read was requested so the data
-		 * must be written back to the guest memory).
+		 * Free the old scratch area and switch to using newly
+		 * allocated.
 		 */
-		svm->sev_es.ghcb_sa_sync = sync;
-		svm->sev_es.ghcb_sa_free = true;
+		kvfree(svm->sev_es.ghcb_sa);
+
+		svm->sev_es.ghcb_sa_alloc_len = len;
+		svm->sev_es.ghcb_sa = scratch_va;
 	}
 
-	svm->sev_es.ghcb_sa = scratch_va;
+	if (kvm_read_guest(svm->vcpu.kvm, scratch_gpa_beg, svm->sev_es.ghcb_sa, len)) {
+		/* Unable to copy scratch area from guest */
+		pr_err("vmgexit: kvm_read_guest for scratch area failed\n");
+		return -EFAULT;
+	}
+
+	/*
+	 * The operation will dictate whether the buffer needs to be synced
+	 * before running the vCPU next time (i.e. a read was requested so
+	 * the data must be written back to the guest memory).
+	 */
+	svm->sev_es.ghcb_sa_sync = sync;
 	svm->sev_es.ghcb_sa_len = len;
 
 	return 0;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index ae733188cf87..f53a41e13033 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -209,8 +209,9 @@  struct vcpu_sev_es_state {
 	/* SEV-ES scratch area support */
 	void *ghcb_sa;
 	u32 ghcb_sa_len;
+	u64 ghcb_sa_gpa;
+	u32 ghcb_sa_alloc_len;
 	bool ghcb_sa_sync;
-	bool ghcb_sa_free;
 };
 
 struct vcpu_svm {