On Tue, Apr 28, 2020 at 09:57:00AM +1000, Gavin Shan wrote:
> Prior to commit 8eb7e28d4c642c31 ("arm64/mm: move runtime pgds to
> rodata"), idmap_pgd_dir, tramp_pg_dir, reserved_ttbr0, swapper_pg_dir,
> and init_pg_dir were contiguous at the end of the kernel image. The
> maintenance at the end of __create_page_tables assumed these were
> contiguous, and affected everything from the start of idmap_pg_dir
> to the end of init_pg_dir.
>
> That commit moved all but init_pg_dir into the .rodata section, with
> other data placed between idmap_pg_dir and init_pg_dir, but did not
> update the maintenance. Hence the maintenance is performed on much
> more data than necessary (but as the bootloader previously made this
> clean to the PoC there is no functional problem).
>
> As we only alter idmap_pg_dir, and init_pg_dir, we only need to perform
> maintenance for these. As the other dirs are in .rodata, the bootloader
> will have initialised them as expected and cleaned them to the PoC. The
> kernel will initialize them as necessary after enabling the MMU.
>
> This patch reworks the maintenance to only cover the idmap_pg_dir and
> init_pg_dir to avoid this unnecessary work.
>
> Signed-off-by: Gavin Shan <[email protected]>
Reviewed-by: Mark Rutland <[email protected]>
Mark.
> ---
> v2: Include the suggested commit log (Mark Rutland)
> Improved comments and code (Mark Rutland)
> ---
> arch/arm64/include/asm/pgtable.h | 1 +
> arch/arm64/kernel/head.S | 12 +++++++++---
> arch/arm64/kernel/vmlinux.lds.S | 1 +
> 3 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h
> b/arch/arm64/include/asm/pgtable.h
> index 8c20e2bd6287..5caff09c6a3a 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -457,6 +457,7 @@ extern pgd_t init_pg_dir[PTRS_PER_PGD];
> extern pgd_t init_pg_end[];
> extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
> extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
> +extern pgd_t idmap_pg_end[];
> extern pgd_t tramp_pg_dir[PTRS_PER_PGD];
>
> extern void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd);
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 57a91032b4c2..32f5ecbec0ea 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -394,13 +394,19 @@ SYM_FUNC_START_LOCAL(__create_page_tables)
>
> /*
> * Since the page tables have been populated with non-cacheable
> - * accesses (MMU disabled), invalidate the idmap and swapper page
> - * tables again to remove any speculatively loaded cache lines.
> + * accesses (MMU disabled), invalidate those tables again to
> + * remove any speculatively loaded cache lines.
> */
> + dmb sy
> +
> adrp x0, idmap_pg_dir
> + adrp x1, idmap_pg_end
> + sub x1, x1, x0
> + bl __inval_dcache_area
> +
> + adrp x0, init_pg_dir
> adrp x1, init_pg_end
> sub x1, x1, x0
> - dmb sy
> bl __inval_dcache_area
>
> ret x28
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 497f9675071d..94402aaf5f5c 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -139,6 +139,7 @@ SECTIONS
>
> idmap_pg_dir = .;
> . += IDMAP_DIR_SIZE;
> + idmap_pg_end = .;
>
> #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
> tramp_pg_dir = .;
> --
> 2.23.0
>
