riscv: Do not allow vmap pud mappings for 3-level page table

The vmalloc_fault() path was removed and to avoid syncing the vmalloc PGD
mappings, they are now preallocated. But if the kernel can use a PUD
mapping (which in sv39 is actually a PGD mapping) for large vmalloc
allocation, it will free the current unused preallocated PGD mapping and
install a new leaf one. Since there is no sync anymore, some page tables
lack this new mapping and that triggers a panic.

So only allow PUD mappings for sv48 and sv57.

Fixes: 7d3332be ("riscv: mm: Pre-allocate PGD entries for vmalloc/modules area")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20230808130709.1502614-1-alexghiti@rivosinc.com
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/vmalloc.h

@@ -3,12 +3,14 @@
 
 #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
 
+extern bool pgtable_l4_enabled, pgtable_l5_enabled;
+
 #define IOREMAP_MAX_ORDER (PUD_SHIFT)
 
 #define arch_vmap_pud_supported arch_vmap_pud_supported
 static inline bool arch_vmap_pud_supported(pgprot_t prot)
 {
-	return true;
+	return pgtable_l4_enabled || pgtable_l5_enabled;
 }
 
 #define arch_vmap_pmd_supported arch_vmap_pmd_supported