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

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>