diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index e0a7549a7c72..83fd49b26a4b 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -641,8 +641,8 @@ static inline void __unused_size_checks(void)
 #define SVM_EVTINJ_TYPE_EXEPT (3 << SVM_EVTINJ_TYPE_SHIFT)
 #define SVM_EVTINJ_TYPE_SOFT (4 << SVM_EVTINJ_TYPE_SHIFT)
 
-#define SVM_EVTINJ_VALID (1 << 31)
-#define SVM_EVTINJ_VALID_ERR (1 << 11)
+#define SVM_EVTINJ_VALID	BIT(31)
+#define SVM_EVTINJ_VALID_ERR	BIT(11)
 
 #define SVM_EVTINJ_RESERVED_BITS ~(SVM_EVTINJ_VEC_MASK | SVM_EVTINJ_TYPE_MASK | \
 				   SVM_EVTINJ_VALID_ERR | SVM_EVTINJ_VALID)
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 8845f469adf3..af0ef678433d 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1502,6 +1502,7 @@ int svm_allocate_nested(struct vcpu_svm *svm)
 	if (!svm->nested.msrpm)
 		goto err_free_vmcb02;
 
+	svm->nested.vmcb02.cpu = -1;
 	svm->nested.initialized = true;
 	return 0;
 
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 93fbfb7d1f65..6427db390b1c 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -4239,6 +4239,7 @@ static int snp_handle_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_
 	struct kvm *kvm = svm->vcpu.kvm;
 	struct kvm_sev_info *sev = to_kvm_sev_info(kvm);
 	sev_ret_code fw_err = 0;
+	u8 tickle = 0;
 	int ret;
 
 	if (!is_sev_snp_guest(&svm->vcpu))
@@ -4246,8 +4247,21 @@ static int snp_handle_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_
 
 	guard(mutex)(&sev->guest_req_mutex);
 
-	if (kvm_read_guest(kvm, req_gpa, sev->guest_req_buf, PAGE_SIZE))
-		return -EIO;
+	if (kvm_read_guest(kvm, req_gpa, sev->guest_req_buf, PAGE_SIZE)) {
+		svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
+		return 1;
+	}
+
+	/*
+	 * "Tickle" the response buffer to verify it's writable before sending
+	 * the request to firmware, which will modify the VMPCK sequence number.
+	 * Note, this is a best effort check and doesn't guard against TOCTOU
+	 * issues.  See below for more information.
+	 */
+	if (kvm_write_guest(kvm, resp_gpa, &tickle, sizeof(tickle))) {
+		svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
+		return 1;
+	}
 
 	data.gctx_paddr = __psp_pa(sev->snp_context);
 	data.req_paddr = __psp_pa(sev->guest_req_buf);
@@ -4262,6 +4276,13 @@ static int snp_handle_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_
 	if (ret && !fw_err)
 		return ret;
 
+	/*
+	 * Exit to userspace if writing the response fails, e.g. if the mapping
+	 * changed between the initial tickle and the actual write, to avoid
+	 * creating an ambiguous failure ABI with the guest.  Don't return an
+	 * error to the guest because firmware already incremented the VMPCK
+	 * sequence number, but there's no way to communicate that to the guest.
+	 */
 	if (kvm_write_guest(kvm, resp_gpa, sev->guest_resp_buf, PAGE_SIZE))
 		return -EIO;
 
@@ -4313,8 +4334,10 @@ static int snp_handle_ext_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t r
 		return -EINVAL;
 
 	if (kvm_read_guest(kvm, req_gpa + offsetof(struct snp_guest_msg_hdr, msg_type),
-			   &msg_type, 1))
-		return -EIO;
+			   &msg_type, 1)) {
+		svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
+		return 1;
+	}
 
 	/*
 	 * As per GHCB spec, requests of type MSG_REPORT_REQ also allow for
@@ -4353,8 +4376,10 @@ static int snp_handle_ext_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t r
 		 * As per GHCB spec (see "SNP Extended Guest Request"), the
 		 * certificate table is terminated by 24-bytes of zeroes.
 		 */
-		if (data_npages && kvm_clear_guest(kvm, data_gpa, 24))
-			return -EIO;
+		if (data_npages && kvm_clear_guest(kvm, data_gpa, 24)) {
+			svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
+			return 1;
+		}
 	}
 
 	return snp_handle_guest_req(svm, req_gpa, resp_gpa);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index fd6264f003a4..487897ef11dd 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3875,14 +3875,25 @@ static int pre_svm_run(struct kvm_vcpu *vcpu)
 	struct vcpu_svm *svm = to_svm(vcpu);
 
 	/*
-	 * If the previous vmrun of the vmcb occurred on a different physical
-	 * cpu, then mark the vmcb dirty and assign a new asid.  Hardware's
-	 * vmcb clean bits are per logical CPU, as are KVM's asid assignments.
+	 * If the previous VMRUN of the VMCB occurred on a different physical
+	 * cpu, then mark the VMCB dirty as hardware's clean bits are per pCPU.
+	 *
+	 * Reset the ASID generation in both VMCBs. This will lead to assigning
+	 * a new ASID now, and then again when switching to the other VMCB.
+	 * However, this is needed as the ASID is shared between the VMCBs, and
+	 * otherwise it would be possible to use an ASID allocated on one pCPU
+	 * on another, for example:
+	 * - vCPU migrates from pCPU A to pCPU B, allocates a new ASID.
+	 * - vCPU migrates back to pCPU A, and then switches the VMCB.
+	 * - The new VMCB does not detect a pCPU change and runs on pCPU A with
+	 *   the new ASID allocated on pCPU B, which is potentially used by
+	 *   another vCPU/VM.
 	 */
 	if (unlikely(svm->current_vmcb->cpu != vcpu->cpu)) {
-		svm->current_vmcb->asid_generation = 0;
 		vmcb_mark_all_dirty(svm->vmcb);
 		svm->current_vmcb->cpu = vcpu->cpu;
+		svm->vmcb01.asid_generation = 0;
+		svm->nested.vmcb02.asid_generation = 0;
         }
 
 	if (is_sev_guest(vcpu))