From 55a77193c7b3bf3bcebf7e75e79b0c615a3a2fb3 Mon Sep 17 00:00:00 2001
From: Arthur Hanson Rasmusson <arthur@vgpu.io>
Date: Wed, 21 Oct 2026 20:51:27 -0400
Subject: r436 full sysmem PTE aperture/VOL matrix: gsp_phys_rmcall_pte_coh
 becomes a 4-mode selector (0=0xf aperture3+VOL historical, 1=0xd
 aperture2+VOL r431, 2=0x5 aperture2 non-volatile, 3=0x7 aperture3
 non-volatile) applied consistently to the leaf PTE and the single PDE (bit0 =
 IS_PDE there), so the r431 finding (aperture 2 with VOL still 1 is a pair the
 reference RM never emits) can be A/B'd against the consistent encodings

---
 kernel/gsp_phys_booter.c | 73 ++++++++++++++++++++++++++++++++----------------
 1 file changed, 49 insertions(+), 24 deletions(-)

(limited to 'kernel/gsp_phys_booter.c')

diff --git a/kernel/gsp_phys_booter.c b/kernel/gsp_phys_booter.c
index 1b8deae..b19fa0d 100644
--- a/kernel/gsp_phys_booter.c
+++ b/kernel/gsp_phys_booter.c
@@ -9626,41 +9626,66 @@ static int gsp_phys_rmcall_golden_replay(void __iomem *bar0)
  * (swref/published/pascal/gp100/dev_mmu.h:97-119,157;
  * uvm_pascal_mmu.c:64-141,235-303).
  */
-static u64 gsp_phys_rmcall_pde(u64 pa)
-{
-	return 0xeull | ((pa >> 12) << 8);
-}
-
 /*
- * r431 COHERENCY ROOT-CAUSE CANDIDATE: the leaf-PTE aperture for every host
- * page this backend maps (the ladder windows, the win0 shadow pool, the
+ * r431/r436 COHERENCY ROOT-CAUSE CANDIDATE: the leaf-PTE aperture for every
+ * host page this backend maps (the ladder windows, the win0 shadow pool, the
  * bounce/data regions, the release/scratch shadows) was hardcoded to
- * aperture 3 = SYSTEM_NON_COHERENT_MEMORY. The reference RM picks the
- * aperture from the allocation's CPU cache attribute
- * (fabric_vaspace.c:1123-1134): NV_MEMORY_CACHED -> SYSTEM_COHERENT (2),
- * otherwise NON_COHERENT (3). Every page here is dma_alloc_coherent (CPU
- * cached/coherent by construction), so 3 is wrong: the GPU's L2 does not
- * snoop the CPU, which makes the engine's stores linger in L2 (the host's
- * retire scan reads stale memory = the "no-execute wedge") and the host's
- * re-staged copy-in content invisible to the engine (the retries re-read
- * stale lines). gsp_phys_rmcall_pte_coh selects aperture 2 (default 1) for
- * a one-flag A/B against the historical 3 (0); the PTEs are planted before
- * the engine's first fetch, so the flag is boot-time only.
- */
-static bool gsp_phys_rmcall_pte_coh_param;
+ * aperture 3 = SYSTEM_NON_COHERENT_MEMORY. The reference RM derives the
+ * pair from the allocation's CPU cache attribute (fabric_vaspace.c:1123-1134
+ * for the aperture, mem_desc.c memdescGetVolatility for VOL: NV_MEMORY_CACHED
+ * -> SYSTEM_COHERENT (2) + volatile FALSE, NV_MEMORY_UNCACHED -> NON_COHERENT
+ * (3) + volatile TRUE). The r431 experiment used aperture 2 with VOL still 1
+ * (0xd) - a pair the reference RM never produces - and it made the engine's
+ * truncated writes visible sooner but worsened the wedge on a fresh boot.
+ * r436 turns the knob into the full 2x2 matrix so each consistent encoding
+ * can be A/B'd:
+ *   0 = aperture 3 + VOL 1 (0xf) - historical, NV_MEMORY_UNCACHED
+ *   1 = aperture 2 + VOL 1 (0xd) - r431 experiment (inconsistent pair)
+ *   2 = aperture 2 + VOL 0 (0x5) - NV_MEMORY_CACHED (coherent, non-volatile)
+ *   3 = aperture 3 + VOL 0 (0x7) - non-coherent, non-volatile
+ * The PTEs are planted before the engine's first fetch, so the flag is
+ * boot-time only.
+ */
+static int gsp_phys_rmcall_pte_coh_param;
 module_param_named(gsp_phys_rmcall_pte_coh, gsp_phys_rmcall_pte_coh_param,
-		   bool, 0444);
+		   int, 0444);
 MODULE_PARM_DESC(gsp_phys_rmcall_pte_coh,
-		 "r431: sysmem leaf-PTE aperture: 1 = SYSTEM_COHERENT (correct for dma_alloc_coherent host pages), 0 = SYSTEM_NON_COHERENT (historical)");
+		 "r436: sysmem leaf-PTE aperture/VOL mode: 0=0xf (aperture3+VOL, historical), 1=0xd (aperture2+VOL, r431), 2=0x5 (aperture2, non-volatile), 3=0x7 (aperture3, non-volatile)");
+
+static u64 gsp_phys_rmcall_sysmem_base_low(void)
+{
+	switch (gsp_phys_rmcall_pte_coh_param) {
+	case 1:
+		return 0xdull;	/* aperture 2, VOL 1 */
+	case 2:
+		return 0x5ull;	/* aperture 2, VOL 0 */
+	case 3:
+		return 0x7ull;	/* aperture 3, VOL 0 */
+	default:
+		return 0xfull;	/* aperture 3, VOL 1 (historical) */
+	}
+}
 
 static u64 gsp_phys_rmcall_pte(u64 pa)
 {
 	/*
 	 * Low nibble: VALID (1) | APERTURE<<1 | VOL (8). Aperture 2 =
 	 * SYSTEM_COHERENT_MEMORY -> 1|4|8 = 0xd; aperture 3 = NON_COHERENT
-	 * -> 1|6|8 = 0xf.
+	 * -> 1|6|8 = 0xf. r436: see gsp_phys_rmcall_pte_coh_param.
 	 */
-	u64 base = gsp_phys_rmcall_pte_coh_param ? 0xdull : 0xfull;
+	u64 base = gsp_phys_rmcall_sysmem_base_low();
+
+	return base | ((pa >> 12) << 8);
+}
+
+/*
+ * r436: the single PDE uses the same aperture/VOL pair as the leaf PTEs but
+ * with IS_PDE=0 in bit 0 (the low bit of the PTE base is VALID there), so the
+ * PDE base is the PTE base with bit 0 cleared: 0xe/0xc/0x4/0x6.
+ */
+static u64 gsp_phys_rmcall_pde(u64 pa)
+{
+	u64 base = gsp_phys_rmcall_sysmem_base_low() & ~1ull;
 
 	return base | ((pa >> 12) << 8);
 }
-- 
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