[PATCH v2] ppc/fadump: collect dump if the collected size is lesser than reserved

[Shivang Upadhyay <shivangu@linux.ibm.com>]

During Fadump in Qemu VM, when maxcpus value is set to more than current
cpus, following failure is observed.

    [0.000000] rtas: Dump taken by platform is incomplete (-1)

This is because the CPU_STATE_DATA is allocated for maxcpus, while the
data is only filled for current cpus. As per current implementation
of Fadump, dumped_bytes and source_len for a region have to match,
Which is failing for qemu's case, Even tough the dumped bytes are
reported correctly for only the current cpus. After this /proc/vmcore
generatition also fails.

Allowing dumped_bytes to be lesser than or equal to allocated length, for
CPU_STATE_DATA Fadump region.

Reported-by: Anushree Mathur <anushree.mathur@linux.vnet.ibm.com>
Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
---
ChangeLog:

v2: Only allowing lesser size for CPU_STATE_DATE Fadump region.

v1: https://lore.kernel.org/qemu-devel/20260429065127.366813-1-shivangu@linux.ibm.com/
---
 arch/powerpc/platforms/pseries/rtas-fadump.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/rtas-fadump.c b/arch/powerpc/platforms/pseries/rtas-fadump.c
index 3bb4ac2ab6cc..ea1a0a8ac9eb 100644
--- a/arch/powerpc/platforms/pseries/rtas-fadump.c
+++ b/arch/powerpc/platforms/pseries/rtas-fadump.c
@@ -459,7 +459,10 @@ static int __init rtas_fadump_process(struct fw_dump *fadump_conf)
 	/* Check if the dump data is valid. */
 	for (int i = 0; i < be16_to_cpu(fdm_active->header.dump_num_sections); i++) {
 		int type = be16_to_cpu(fdm_active->rgn[i].source_data_type);
+		uint64_t bytes_dumped = be64_to_cpu(fdm_active->rgn[i].bytes_dumped);
+		uint64_t source_len = be64_to_cpu(fdm_active->rgn[i].source_len);
 		int rc = 0;
+		int region_collected;
 
 		switch (type) {
 		case RTAS_FADUMP_CPU_STATE_DATA:
@@ -469,8 +472,18 @@ static int __init rtas_fadump_process(struct fw_dump *fadump_conf)
 				pr_err("Dump taken by platform is not valid (%d)\n", i);
 				rc = -EINVAL;
 			}
-			if (fdm_active->rgn[i].bytes_dumped != fdm_active->rgn[i].source_len) {
+			/*
+			 * Make sure that dump is collected for entire region.
+			 * CPU_STATE_DATA region is allowed to dump less than allocated space.
+			 */
+			region_collected = (bytes_dumped == source_len ||
+	                         (type == RTAS_FADUMP_CPU_STATE_DATA && bytes_dumped <= source_len));
+
+
+			if (! region_collected) {
 				pr_err("Dump taken by platform is incomplete (%d)\n", i);
+				pr_debug("type -> %d, bytes_dumped -> %llx, source_len -> %llx\n",
+				         type, bytes_dumped, source_len);
 				rc = -EINVAL;
 			}
 			if (rc) {
@@ -482,7 +495,7 @@ static int __init rtas_fadump_process(struct fw_dump *fadump_conf)
 			}
 			break;
 		case RTAS_FADUMP_PARAM_AREA:
-			if (fdm_active->rgn[i].bytes_dumped != fdm_active->rgn[i].source_len ||
+			if (bytes_dumped != source_len ||
 			    fdm_active->rgn[i].error_flags != 0) {
 				pr_warn("Failed to process additional parameters! Proceeding anyway..\n");
 				fadump_conf->param_area = 0;
-- 
2.54.0