vgsp-sema: log release writes into the UVM sysmem semaphore range (ISSUE-0002 diagnosis)

Bounded instrumentation: every svc_sem_write into 0x7924_xxxx_xxxx..0x7926
records (h, va, pa, aperture, resolver provenance, value, write rc,
read-back ok/value, pool) so the second session's translations for the
same VAs can be compared against the first session's. The second client
spins in uvm_gpu_retain_by_uuid -> uvm_page_tree_init ->
uvm_push_end_and_wait -> wait_for_entry_with_spin (guest kernel stack,
sysrq-l) waiting on the channel tracking semaphore; these lines will
name the PA the release landed at.

1 files changed, 16 insertions, 2 deletions

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index e6459f3..e127a4a 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -538,6 +538,7 @@ struct sema_svc {
 	u64			copy_pat_log;		/* sema_copy_pat log budget */
 	u64			copy_dst_log;		/* sema_copy_dst log budget */
 	u32			op_tr_src;		/* provenance of last svc_op_translate */
+	u32			sem_sw_log;		/* sema-sw release-write log budget */
 	u64			push_pat_log;		/* push-content pattern budget */
 	u64			dma_skip_log;		/* unrecognized-DMA budget */
 	u64			xfer_raw_log;		/* operandless transfer raw-dump budget */
@@ -2610,6 +2611,7 @@ static int svc_sem_write(struct nv_vgpu_device *vgpu, u32 h, u64 va, u32 val)
 	bool is_pool = svc_pool_sem_va(va);
 	int wap, rc;
 	bool verified = false;
+	bool rb_ok = false;
 
 	/*
 	 * Pool semaphores resolve pin -> verified cache -> targeted rm_mem
@@ -2663,8 +2665,20 @@ static int svc_sem_write(struct nv_vgpu_device *vgpu, u32 h, u64 va, u32 val)
 	if (is_pool)
 		(void)svc_read_ap(vgpu, addr, wap, &cur, sizeof(cur));
 	rc = svc_write_ap(vgpu, addr, wap, &val, sizeof(val));
-	if (!rc && !svc_read_ap(vgpu, addr, wap, &back, sizeof(back)) &&
-	    back == val) {
+	rb_ok = !rc && !svc_read_ap(vgpu, addr, wap, &back, sizeof(back));
+	/*
+	 * ISSUE-0002 diagnosis: record every release write into UVM's
+	 * sysmem semaphore range (0x792..), with the resolver provenance and
+	 * the read-back, so the second session's translations can be
+	 * compared with the first session's for the same VA. Bounded.
+	 */
+	if (va >= 0x79240000000ULL && va < 0x79260000000ULL &&
+	    svc.sem_sw_log < 8192) {
+		svc.sem_sw_log++;
+		pr_info("sema-sw: h=0x%x va=0x%llx pa=0x%llx ap=%d src=%s val=0x%x rc=%d rb_ok=%d back=0x%x pool=%d\n",
+			h, va, addr, wap, src, val, rc, rb_ok, back, is_pool);
+	}
+	if (rb_ok && back == val) {
 		if (is_pool)
 			svc_pool_wr_note(h, va, addr, src, cur, val, "ok");
 		return 0;