vgsp: fix per-type VRAM type lookup and canonical FB-size encoding

The 549d1e81 per-type VRAM change stripped an nvidia- prefix from
mdev->type->sysfs_name, but sysfs_name is the registered type name
verbatim; the mdev core only prefixes the type DIRECTORY with the parent
driver string. Every lookup failed, so all mdevs silently fell back to
512 MiB, nvidia-vgpu-turing-1g was unreachable and available_instances
capped at 1. Match sysfs_name directly in get_available,
show_description and mdev_create.

Also canonicalise the NV_PFB_PRI_MMU_LOCAL_MEMORY_RANGE encoder
(BAR0+0x100ce0) by stripping factors of two from MAG so 512 MiB encodes
0x19 again (1 GiB 0x1a, 2 GiB 0x1b) instead of the non-canonical 0x204.

Default-512M behaviour is now byte-equivalent to the known-good pre-VRAM
module except max_instances=2. Module sha256 cb1724d3.

2 files changed, 25 insertions, 13 deletions

diff --git a/kernel/bar_emulation.c b/kernel/bar_emulation.c
index 8e3f8cf..d1702c8 100644
--- a/kernel/bar_emulation.c
+++ b/kernel/bar_emulation.c
@@ -290,13 +290,24 @@ int nv_vgpu_bar_emul_init(struct nv_vgpu_device *vgpu)
 		 * guest's fbSize - reserved arithmetic stays consistent.
 		 */
 		u64 fb = nv_vgpu_fb_emul_size(ctx->vgpu);
-		u32 scale = 0;
+		u32 scale = 0, mag;
 
+		/*
+		 * Find the largest SCALE whose MAG fits the 6-bit field, then
+		 * canonicalise: strip factors of two from MAG while SCALE can
+		 * absorb them. 512 MiB -> mag=1,scale=9 -> 0x19 (the historical
+		 * known-good value); 1 GiB -> 0x1a; 2 GiB -> 0x1b. Sizes that
+		 * are not exactly representable round down.
+		 */
 		while (scale < 15 && (fb >> (scale + 20)) > 0x3f)
 			scale++;
+		mag = (u32)(fb >> (scale + 20));
+		while (scale < 15 && mag > 1 && !(mag & 1u)) {
+			mag >>= 1;
+			scale++;
+		}
 		*(u32 *)((u8 *)ctx->bar0_shadow + 0x100ce0) =
-			((((u32)(fb >> (scale + 20))) & 0x3f) << 4) |
-			(scale & 0xf);
+			((mag & 0x3f) << 4) | (scale & 0xf);
 	}
 
 	/*
diff --git a/kernel/main.c b/kernel/main.c
index a5a64fd..f662b94 100644
--- a/kernel/main.c
+++ b/kernel/main.c
@@ -85,10 +85,13 @@ static unsigned int nv_vgpu_get_available(struct mdev_type *mtype)
 	const char *name = mtype->sysfs_name;
 	unsigned int active = 0, max = 1;
 
-	/* Type dirs may carry an extra "nvidia-" prefix vs our type names */
-	if (str_has_prefix(name, "nvidia-"))
-		name += strlen("nvidia-");
-	info = nv_vgpu_find_type_info(name);
+	/*
+	 * sysfs_name is our registered type name verbatim ("nvidia-vgpu-*").
+	 * The mdev core prefixes only the type DIRECTORY with the parent
+	 * driver string (mdev_type_add: "%s-%s", dev_driver_string, sysfs_name);
+	 * it does not touch sysfs_name. Match it directly.
+	 */
+	info = name ? nv_vgpu_find_type_info(name) : NULL;
 	if (info && info->max_instances)
 		max = info->max_instances;
 
@@ -116,8 +119,7 @@ static ssize_t nv_vgpu_show_description(struct mdev_type *mtype, char *buf)
 	const char *name = mtype->sysfs_name;
 	u32 vram_mb = 512, max_inst = 1;
 
-	if (name && str_has_prefix(name, "nvidia-"))
-		name += strlen("nvidia-");
+	/* sysfs_name is the registered type name; match it directly. */
 	info = name ? nv_vgpu_find_type_info(name) : NULL;
 	if (info) {
 		if (info->vram_mb)
@@ -563,15 +565,14 @@ static int nv_vgpu_mdev_create(struct mdev_device *mdev)
  	vgpu->state = NV_VGPU_STATE_UNINITIALIZED;
 	/*
 	 * Bind the emulated FB size to this mdev's type (the type's vram_mb;
-	 * 0/absent keeps the 512 MiB default). The type dir may carry an
-	 * extra "nvidia-" prefix vs our registered names.
+	 * 0/absent keeps the 512 MiB default). sysfs_name is the registered
+	 * type name verbatim; match it directly (the mdev core only prefixes
+	 * the type directory with the parent driver string).
 	 */
 	{
 		const char *tname = mdev->type ? mdev->type->sysfs_name : NULL;
 		struct nv_vgpu_type_info *tinfo;
 
-		if (tname && str_has_prefix(tname, "nvidia-"))
-			tname += strlen("nvidia-");
 		tinfo = tname ? nv_vgpu_find_type_info(tname) : NULL;
 		vgpu->fb_emul_size = (tinfo && tinfo->vram_mb) ?
 			(u64)tinfo->vram_mb << 20 : NV_VGPU_EMUL_FB_SIZE;