Commit 3b5657ed authored by Michael Ellerman's avatar Michael Ellerman

powerpc/mm/radix: Fix overuse of small pages in splitting logic

When we have CONFIG_STRICT_KERNEL_RWX enabled, we want to split the
linear mapping at the text/data boundary so we can map the kernel text
read only.

But the current logic uses small pages for the entire text section,
regardless of whether a larger page size would fit. eg. with the
boundary at 16M we could use 2M pages, but instead we use 64K pages up
to the 16M boundary:

  Mapped 0x0000000000000000-0x0000000001000000 with 64.0 KiB pages
  Mapped 0x0000000001000000-0x0000000040000000 with 2.00 MiB pages
  Mapped 0x0000000040000000-0x0000000100000000 with 1.00 GiB pages

This is because the test is checking if addr is < __init_begin
and addr + mapping_size is >= _stext. But that is true for all pages
between _stext and __init_begin.

Instead what we want to check is if we are crossing the text/data
boundary, which is at __init_begin. With that fixed we see:

  Mapped 0x0000000000000000-0x0000000000e00000 with 2.00 MiB pages
  Mapped 0x0000000000e00000-0x0000000001000000 with 64.0 KiB pages
  Mapped 0x0000000001000000-0x0000000040000000 with 2.00 MiB pages
  Mapped 0x0000000040000000-0x0000000100000000 with 1.00 GiB pages

ie. we're correctly using 2MB pages below __init_begin, but we still
drop down to 64K pages unnecessarily at the boundary.
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 5c6499b7
...@@ -295,14 +295,14 @@ static int __meminit create_physical_mapping(unsigned long start, ...@@ -295,14 +295,14 @@ static int __meminit create_physical_mapping(unsigned long start,
if (split_text_mapping && (mapping_size == PUD_SIZE) && if (split_text_mapping && (mapping_size == PUD_SIZE) &&
(addr < __pa_symbol(__init_begin)) && (addr < __pa_symbol(__init_begin)) &&
(addr + mapping_size) >= __pa_symbol(_stext)) { (addr + mapping_size) >= __pa_symbol(__init_begin)) {
max_mapping_size = PMD_SIZE; max_mapping_size = PMD_SIZE;
goto retry; goto retry;
} }
if (split_text_mapping && (mapping_size == PMD_SIZE) && if (split_text_mapping && (mapping_size == PMD_SIZE) &&
(addr < __pa_symbol(__init_begin)) && (addr < __pa_symbol(__init_begin)) &&
(addr + mapping_size) >= __pa_symbol(_stext)) { (addr + mapping_size) >= __pa_symbol(__init_begin)) {
mapping_size = PAGE_SIZE; mapping_size = PAGE_SIZE;
psize = mmu_virtual_psize; psize = mmu_virtual_psize;
} }
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment