riscv: mm: Fix the out of bound issue of vmemmap address

commit f754f27e98f88428aaf6be6e00f5cbce97f62d4b upstream.

In sparse vmemmap model, the virtual address of vmemmap is calculated as:
((struct page *)VMEMMAP_START - (phys_ram_base >> PAGE_SHIFT)).
And the struct page's va can be calculated with an offset:
(vmemmap + (pfn)).

However, when initializing struct pages, kernel actually starts from the
first page from the same section that phys_ram_base belongs to. If the
first page's physical address is not (phys_ram_base >> PAGE_SHIFT), then
we get an va below VMEMMAP_START when calculating va for it's struct page.

For example, if phys_ram_base starts from 0x82000000 with pfn 0x82000, the
first page in the same section is actually pfn 0x80000. During
init_unavailable_range(), we will initialize struct page for pfn 0x80000
with virtual address ((struct page *)VMEMMAP_START - 0x2000), which is
below VMEMMAP_START as well as PCI_IO_END.

This commit fixes this bug by introducing a new variable
'vmemmap_start_pfn' which is aligned with memory section size and using
it to calculate vmemmap address instead of phys_ram_base.

Fixes: a11dd49dcb93 ("riscv: Sparse-Memory/vmemmap out-of-bounds fix")
Signed-off-by: Xu Lu <luxu.kernel@bytedance.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20241209122617.53341-1-luxu.kernel@bytedance.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Zhaoyang Li <lizy04@hust.edu.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/riscv/include/asm/page.h

@@ -115,6 +115,7 @@ struct kernel_mapping {
 
 extern struct kernel_mapping kernel_map;
 extern phys_addr_t phys_ram_base;
+extern unsigned long vmemmap_start_pfn;
 
 #define is_kernel_mapping(x)	\
 	((x) >= kernel_map.virt_addr && (x) < (kernel_map.virt_addr + kernel_map.size))

arch/riscv/include/asm/pgtable.h

@@ -79,7 +79,7 @@
  * Define vmemmap for pfn_to_page & page_to_pfn calls. Needed if kernel
  * is configured with CONFIG_SPARSEMEM_VMEMMAP enabled.
  */
-#define vmemmap		((struct page *)VMEMMAP_START - (phys_ram_base >> PAGE_SHIFT))
+#define vmemmap		((struct page *)VMEMMAP_START - vmemmap_start_pfn)
 
 #define PCI_IO_SIZE      SZ_16M
 #define PCI_IO_END       VMEMMAP_START

arch/riscv/mm/init.c

@@ -22,6 +22,7 @@
 #include <linux/hugetlb.h>
 
 #include <asm/fixmap.h>
+#include <asm/sparsemem.h>
 #include <asm/tlbflush.h>
 #include <asm/sections.h>
 #include <asm/soc.h>
@@ -52,6 +53,13 @@ EXPORT_SYMBOL(pgtable_l5_enabled);
 phys_addr_t phys_ram_base __ro_after_init;
 EXPORT_SYMBOL(phys_ram_base);
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+#define VMEMMAP_ADDR_ALIGN	(1ULL << SECTION_SIZE_BITS)
+
+unsigned long vmemmap_start_pfn __ro_after_init;
+EXPORT_SYMBOL(vmemmap_start_pfn);
+#endif
+
 unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
 							__page_aligned_bss;
 EXPORT_SYMBOL(empty_zero_page);
@@ -210,8 +218,12 @@ static void __init setup_bootmem(void)
 	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
 
 	phys_ram_end = memblock_end_of_DRAM();
-	if (!IS_ENABLED(CONFIG_XIP_KERNEL))
+	if (!IS_ENABLED(CONFIG_XIP_KERNEL)) {
 		phys_ram_base = memblock_start_of_DRAM();
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+		vmemmap_start_pfn = round_down(phys_ram_base, VMEMMAP_ADDR_ALIGN) >> PAGE_SHIFT;
+#endif
+}
 	/*
 	 * Reserve physical address space that would be mapped to virtual
 	 * addresses greater than (void *)(-PAGE_SIZE) because:
@@ -946,6 +958,9 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	kernel_map.xiprom_sz = (uintptr_t)(&_exiprom) - (uintptr_t)(&_xiprom);
 
 	phys_ram_base = CONFIG_PHYS_RAM_BASE;
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+	vmemmap_start_pfn = round_down(phys_ram_base, VMEMMAP_ADDR_ALIGN) >> PAGE_SHIFT;
+#endif
 	kernel_map.phys_addr = (uintptr_t)CONFIG_PHYS_RAM_BASE;
 	kernel_map.size = (uintptr_t)(&_end) - (uintptr_t)(&_start);