sev-guest: configfs-tsm: Allow the privlevel_floor attribute to be updated

With the introduction of an SVSM, Linux will be running at a non-zero
VMPL. Any request for an attestation report at a higher privilege VMPL
than what Linux is currently running will result in an error. Allow for
the privlevel_floor attribute to be updated dynamically.

  [ bp: Trim commit message. ]
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/5a736be9384aebd98a0b7c929660f8a97cbdc366.1717600736.git.thomas.lendacky@amd.com

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

@@ -892,7 +892,7 @@ static int sev_report_new(struct tsm_report *report, void *data)
 	return 0;
 }
 
-static const struct tsm_ops sev_tsm_ops = {
+static struct tsm_ops sev_tsm_ops = {
 	.name = KBUILD_MODNAME,
 	.report_new = sev_report_new,
 };
@@ -979,6 +979,9 @@ static int __init sev_guest_probe(struct platform_device *pdev)
 	snp_dev->input.resp_gpa = __pa(snp_dev->response);
 	snp_dev->input.data_gpa = __pa(snp_dev->certs_data);
 
+	/* Set the privlevel_floor attribute based on the vmpck_id */
+	sev_tsm_ops.privlevel_floor = vmpck_id;
+
 	ret = tsm_register(&sev_tsm_ops, snp_dev, &tsm_report_extra_type);
 	if (ret)
 		goto e_free_cert_data;

include/linux/tsm.h

@@ -54,7 +54,7 @@ struct tsm_report {
  */
 struct tsm_ops {
 	const char *name;
-	const unsigned int privlevel_floor;
+	unsigned int privlevel_floor;
 	int (*report_new)(struct tsm_report *report, void *data);
 };