vgsp-gl: follow migrated screen pages in the GR copy-out

2 files changed, 71 insertions, 1 deletions

diff --git a/kernel/gsp_phys_booter.c b/kernel/gsp_phys_booter.c
index 96fdc46..5f8df5e 100644
--- a/kernel/gsp_phys_booter.c
+++ b/kernel/gsp_phys_booter.c
@@ -18715,6 +18715,28 @@ bool gsp_phys_rmcall_gr_raster_pre_value(void)
 }
 
 /*
+ * SESSION 155 CONT 18: follow a migrated screen page instead of skipping
+ * its write-back. The guest's video-memory manager migrates the X screen
+ * BO (the WGUARD-SKIP "used != now" case); the drawn content then sits in
+ * the bounce copy of the old page and is currently discarded. When this
+ * knob is on and the stale VA belongs to the captured screen surface, the
+ * page is written to the VA's CURRENT mapping (receipt
+ * WGUARD-STALE-WRITE) so the guest sees the frame. Off = the historical
+ * safe skip.
+ */
+static bool gsp_phys_gr_stale_write;
+static u32 gsp_phys_gr_stale_log;	/* CONT 18 */
+module_param_named(sema_gl_stale_write, gsp_phys_gr_stale_write, bool,
+		   0644);
+MODULE_PARM_DESC(sema_gl_stale_write,
+	"Write a copy-out page to the screen VA's current mapping when the write guard reports a migration (default 0; safe skip)");
+
+bool gsp_phys_rmcall_gr_stale_write_value(void)
+{
+	return READ_ONCE(gsp_phys_gr_stale_write);
+}
+
+/*
  * SESSION 155 CONT 15: where the synthesized GS SPH lives inside the
  * program-family page. 0 = family+0x780 (below the window's own VTG bind
  * at family+0x900), 1 = family+0xe80 (above it; the DS's PROGRAM_REGION
@@ -33179,7 +33201,49 @@ gr_page_unmapped:
 			if (!gsp_sema_gr_write_guard(req->data[wbi].va,
 						     req->data[wbi].hpa,
 						     "gr-bounce-copy-out")) {
-				skipped++;
+				/*
+				 * CONT 18: a migrated screen page - follow
+				 * the VA's current mapping instead of
+				 * dropping the frame (see the knob).
+				 */
+				bool followed = false;
+
+				if (READ_ONCE(gsp_phys_gr_stale_write)) {
+					u64 sva = 0;
+					u32 snp = 0;
+
+					if (gsp_sema_surf_va_get(&sva, &snp) &&
+					    sva &&
+					    req->data[wbi].va >= sva &&
+					    req->data[wbi].va <
+					    sva + ((u64)snp << 12)) {
+						u64 rpa = 0, rval = 0;
+						u32 rap = 0;
+
+						if (gsp_sema_gr_va_snap(
+							    req->data[wbi].va,
+							    &rpa, &rap, &rval) &&
+						    rpa) {
+							memcpy((u8 *)__va(rpa),
+							       src,
+							       GSP_PHYS_PAGE_SIZE);
+							followed = true;
+							if (gsp_phys_gr_stale_log <
+							    64u) {
+								gsp_phys_gr_stale_log++;
+								pr_info("vgsp-gr: WGUARD-STALE-WRITE va=0x%llx used=0x%llx now=0x%llx h=0x%x push=0x%llx\n",
+									req->data[wbi].va,
+									req->data[wbi].hpa,
+									rpa,
+									req->h_object,
+									req->push_va);
+							}
+							wrote++;
+						}
+					}
+				}
+				if (!followed)
+					skipped++;
 				continue;
 			}
 			memcpy((u8 *)__va(req->data[wbi].hpa), src,
diff --git a/kernel/gsp_phys_gpu.h b/kernel/gsp_phys_gpu.h
index d84cd41..f74fff1 100644
--- a/kernel/gsp_phys_gpu.h
+++ b/kernel/gsp_phys_gpu.h
@@ -375,6 +375,12 @@ u32 gsp_phys_rmcall_gr_sph_gs_mode_value(void);
 bool gsp_phys_rmcall_gr_raster_pre_value(void);
 
 /*
+ * SESSION 155 CONT 18: follow a migrated screen page in the copy-out
+ * (sema_gl_stale_write).
+ */
+bool gsp_phys_rmcall_gr_stale_write_value(void);
+
+/*
  * SESSION 155 CONT 15: synthesized GS SPH placement/maps/context A/B.
  */
 u32 gsp_phys_rmcall_gr_sph_gs_addr_value(void);