6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nam Cao namcao@linutronix.de
[ Upstream commit c67ddf59ac44adc60649730bf8347e37c516b001 ]
debug_pagealloc is a debug feature which clears the valid bit in page table entry for freed pages to detect illegal accesses to freed memory.
For this feature to work, virtual mapping must have PAGE_SIZE resolution. (No, we cannot map with huge pages and split them only when needed; because pages can be allocated/freed in atomic context and page splitting cannot be done in atomic context)
Force linear mapping to use small pages if debug_pagealloc is enabled.
Note that it is not necessary to force the entire linear mapping, but only those that are given to memory allocator. Some parts of memory can keep using huge page mapping (for example, kernel's executable code). But these parts are minority, so keep it simple. This is just a debug feature, some extra overhead should be acceptable.
Fixes: 5fde3db5eb02 ("riscv: add ARCH_SUPPORTS_DEBUG_PAGEALLOC support") Signed-off-by: Nam Cao namcao@linutronix.de Cc: stable@vger.kernel.org Reviewed-by: Alexandre Ghiti alexghiti@rivosinc.com Link: https://lore.kernel.org/r/2e391fa6c6f9b3fcf1b41cefbace02ee4ab4bf59.171575093... Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/mm/init.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c index 4d62f54698b99..8adcb9419ad50 100644 --- a/arch/riscv/mm/init.c +++ b/arch/riscv/mm/init.c @@ -668,6 +668,9 @@ 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;