Merge patch series "riscv: fix debug_pagealloc"

Nam Cao <namcao@linutronix.de> says:

The debug_pagealloc feature is not functional on RISCV. With this feature
enabled (CONFIG_DEBUG_PAGEALLOC=y and debug_pagealloc=on), kernel crashes
early during boot.

QEMU command that can reproduce this problem:
   qemu-system-riscv64 -machine virt \
   -kernel Image \
   -append "console=ttyS0 root=/dev/vda debug_pagealloc=on" \
   -nographic \
   -drive "file=root.img,format=raw,id=hd0" \
   -device virtio-blk-device,drive=hd0 \
   -m 4G \

This series makes debug_pagealloc functional.

* b4-shazam-merge:
  riscv: rewrite __kernel_map_pages() to fix sleeping in invalid context
  riscv: force PAGE_SIZE linear mapping if debug_pagealloc is enabled

Link: https://lore.kernel.org/r/cover.1715750938.git.namcao@linutronix.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: palmer-dabbelt

arch/riscv/mm/init.c

@@ -683,6 +683,9 @@ void __init create_pgd_mapping(pgd_t *pgdp,
 static uintptr_t __init best_map_size(phys_addr_t pa, uintptr_t va,
 				      phys_addr_t size)
 {
+	if (debug_pagealloc_enabled())
+		return PAGE_SIZE;
+
 	if (pgtable_l5_enabled &&
 	    !(pa & (P4D_SIZE - 1)) && !(va & (P4D_SIZE - 1)) && size >= P4D_SIZE)
 		return P4D_SIZE;

arch/riscv/mm/pageattr.c

@@ -387,17 +387,33 @@ int set_direct_map_default_noflush(struct page *page)
 }
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
+static int debug_pagealloc_set_page(pte_t *pte, unsigned long addr, void *data)
+{
+	int enable = *(int *)data;
+
+	unsigned long val = pte_val(ptep_get(pte));
+
+	if (enable)
+		val |= _PAGE_PRESENT;
+	else
+		val &= ~_PAGE_PRESENT;
+
+	set_pte(pte, __pte(val));
+
+	return 0;
+}
+
 void __kernel_map_pages(struct page *page, int numpages, int enable)
 {
 	if (!debug_pagealloc_enabled())
 		return;
 
-	if (enable)
-		__set_memory((unsigned long)page_address(page), numpages,
-			     __pgprot(_PAGE_PRESENT), __pgprot(0));
-	else
-		__set_memory((unsigned long)page_address(page), numpages,
-			     __pgprot(0), __pgprot(_PAGE_PRESENT));
+	unsigned long start = (unsigned long)page_address(page);
+	unsigned long size = PAGE_SIZE * numpages;
+
+	apply_to_existing_page_range(&init_mm, start, size, debug_pagealloc_set_page, &enable);
+
+	flush_tlb_kernel_range(start, start + size);
 }
 #endif