[PATCH AUTOSEL 4.19 094/237] powerpc/mm/radix: Fix small page at boundary when splitting

Sasha Levin
2019-11-16T15:43:16Z

From: Michael Ellerman <mpe@ellerman.id.au>

[ Upstream commit 81d1b54dec95209ab5e5be2cf37182885f998753 ]

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.

Currently we always use a small page at the text/data boundary, even
when that's not necessary:

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

This is because the check that the mapping crosses the __init_begin
boundary is too strict, it also returns true when we map exactly up to
the boundary.

So fix it to check that the mapping would actually map past
__init_begin, and with that we see:

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

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/mm/pgtable-radix.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
index b387c7b917b7e..69caeb5bccb21 100644
--- a/arch/powerpc/mm/pgtable-radix.c
+++ b/arch/powerpc/mm/pgtable-radix.c
@@ -295,14 +295,14 @@ static int __meminit create_physical_mapping(unsigned long start,

if (split_text_mapping && (mapping_size == PUD_SIZE) &&
(addr < __pa_symbol(__init_begin)) &&
- (addr + mapping_size) >= __pa_symbol(__init_begin)) {
+ (addr + mapping_size) > __pa_symbol(__init_begin)) {
max_mapping_size = PMD_SIZE;
goto retry;
}

if (split_text_mapping && (mapping_size == PMD_SIZE) &&
(addr < __pa_symbol(__init_begin)) &&
- (addr + mapping_size) >= __pa_symbol(__init_begin)) {
+ (addr + mapping_size) > __pa_symbol(__init_begin)) {
mapping_size = PAGE_SIZE;
psize = mmu_virtual_psize;
}
--
2.20.1