vgsp: m86 - sticky gsp_phys_rmcall_gr_override_hex module parameter

The override blob can now be supplied at load (hex string, <= 1 page) and is
parsed at the first forwarded launch, so the minimal-kernel experiment no
longer depends on a debugfs write racing the guest's launch. Also observed in
the m86 attempt: after many failed launches the forwarded ring desynced
(USERD GP_PUT rewound to 1 while the engine's GP_GET was 513; IQ2M sentinel
intact, no FE fetch) - a fresh boot is required per experiment.

1 files changed, 33 insertions, 0 deletions

diff --git a/kernel/gsp_phys_booter.c b/kernel/gsp_phys_booter.c
index d7ba43d..ee433e1 100644
--- a/kernel/gsp_phys_booter.c
+++ b/kernel/gsp_phys_booter.c
@@ -15539,6 +15539,38 @@ static u64 gsp_phys_gr_pool_exhausted;
 /* m86: program-page override blob (see gsp-phys-gr-override). */
 static u8 gsp_phys_gr_override[GSP_PHYS_PAGE_SIZE];
 static u32 gsp_phys_gr_override_len;
+static bool gsp_phys_gr_override_parsed;
+
+/* m86: parse the sticky hex override parameter once, before first use. */
+static void gsp_phys_gr_override_apply_param(void)
+{
+	const char *h = gsp_phys_rmcall_gr_override_hex_value();
+	u32 n, i;
+
+	if (gsp_phys_gr_override_parsed)
+		return;
+	gsp_phys_gr_override_parsed = true;
+	if (!h || !h[0] || READ_ONCE(gsp_phys_gr_override_len))
+		return;
+	n = (u32)strlen(h);
+	if (n % 2 || n / 2 > GSP_PHYS_PAGE_SIZE) {
+		pr_warn("vgsp-boot: gr-override hex param ignored (bad length %u)\n",
+			n);
+		return;
+	}
+	for (i = 0; i < n; i += 2) {
+		unsigned int b;
+
+		if (sscanf(h + i, "%2x", &b) != 1) {
+			pr_warn("vgsp-boot: gr-override hex param bad at %u\n",
+				i);
+			return;
+		}
+		gsp_phys_gr_override[i / 2] = (u8)b;
+	}
+	WRITE_ONCE(gsp_phys_gr_override_len, n / 2);
+	pr_info("vgsp-boot: gr-override hex param: %u bytes stored\n", n / 2);
+}
 
 void gsp_phys_backend_gr_counters(u64 *submitted, u64 *ok, u64 *refused,
 				  u64 *timed_out, u64 *pool_exhausted)
@@ -16114,6 +16146,7 @@ int gsp_phys_backend_guest_gr_submit(const struct gsp_phys_gr_submit *req,
 	}
 
 	gsp_phys_gr_submitted++;
+	gsp_phys_gr_override_apply_param();
 	mutex_lock(&gsp_phys_rm_lock);
 	if (!gsp_phys_backend_gr_ready()) {
 		mutex_unlock(&gsp_phys_rm_lock);