virt: sev-guest: Reduce the scope of SNP command mutex

The SNP command mutex is used to serialize access to the shared buffer,
command handling, and message sequence number.

All shared buffer, command handling, and message sequence updates are done
within snp_send_guest_request(), so moving the mutex to this function is
appropriate and maintains the critical section.

Since the mutex is now taken at a later point in time, remove the lockdep
checks that occur before taking the mutex.

Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20241009092850.197575-6-nikunj@amd.com

drivers/virt/coco/sev-guest/sev-guest.c

@@ -345,6 +345,14 @@ static int snp_send_guest_request(struct snp_guest_dev *snp_dev, struct snp_gues
 	u64 seqno;
 	int rc;
 
+	guard(mutex)(&snp_cmd_mutex);
+
+	/* Check if the VMPCK is not empty */
+	if (is_vmpck_empty(snp_dev)) {
+		dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
+		return -ENOTTY;
+	}
+
 	/* Get message sequence and verify that its a non-zero */
 	seqno = snp_get_msg_seqno(snp_dev);
 	if (!seqno)
@@ -401,8 +409,6 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
 	struct snp_guest_req req = {};
 	int rc, resp_len;
 
-	lockdep_assert_held(&snp_cmd_mutex);
-
 	if (!arg->req_data || !arg->resp_data)
 		return -EINVAL;
 
@@ -449,8 +455,6 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
 	/* Response data is 64 bytes and max authsize for GCM is 16 bytes. */
 	u8 buf[64 + 16];
 
-	lockdep_assert_held(&snp_cmd_mutex);
-
 	if (!arg->req_data || !arg->resp_data)
 		return -EINVAL;
 
@@ -501,8 +505,6 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
 	int ret, npages = 0, resp_len;
 	sockptr_t certs_address;
 
-	lockdep_assert_held(&snp_cmd_mutex);
-
 	if (sockptr_is_null(io->req_data) || sockptr_is_null(io->resp_data))
 		return -EINVAL;
 
@@ -598,15 +600,6 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
 	if (!input.msg_version)
 		return -EINVAL;
 
-	mutex_lock(&snp_cmd_mutex);
-
-	/* Check if the VMPCK is not empty */
-	if (is_vmpck_empty(snp_dev)) {
-		dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
-		mutex_unlock(&snp_cmd_mutex);
-		return -ENOTTY;
-	}
-
 	switch (ioctl) {
 	case SNP_GET_REPORT:
 		ret = get_report(snp_dev, &input);
@@ -628,8 +621,6 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
 		break;
 	}
 
-	mutex_unlock(&snp_cmd_mutex);
-
 	if (input.exitinfo2 && copy_to_user(argp, &input, sizeof(input)))
 		return -EFAULT;
 
@@ -744,8 +735,6 @@ static int sev_svsm_report_new(struct tsm_report *report, void *data)
 	man_len = SZ_4K;
 	certs_len = SEV_FW_BLOB_MAX_SIZE;
 
-	guard(mutex)(&snp_cmd_mutex);
-
 	if (guid_is_null(&desc->service_guid)) {
 		call_id = SVSM_ATTEST_CALL(SVSM_ATTEST_SERVICES);
 	} else {
@@ -880,14 +869,6 @@ static int sev_report_new(struct tsm_report *report, void *data)
 	if (!buf)
 		return -ENOMEM;
 
-	guard(mutex)(&snp_cmd_mutex);
-
-	/* Check if the VMPCK is not empty */
-	if (is_vmpck_empty(snp_dev)) {
-		dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
-		return -ENOTTY;
-	}
-
 	cert_table = buf + report_size;
 	struct snp_ext_report_req ext_req = {
 		.data = { .vmpl = desc->privlevel },