linux-kernel - Re: [PATCH v2 2/3] arm64: mm: don't call page table ctors for init

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Message-ID: <20190226151307.GB20230@lakrids.cambridge.arm.com>
Date:   Tue, 26 Feb 2019 15:13:07 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Jun Yao <yaojun8558363@...il.com>,
        Laura Abbott <labbott@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/3] arm64: mm: don't call page table ctors for init_mm

Hi,

On Mon, Feb 18, 2019 at 04:13:18PM -0700, Yu Zhao wrote:
> init_mm doesn't require page table lock to be initialized at
> any level. Add a separate page table allocator for it, and the
> new one skips page table ctors.

Just to check, in a previous reply you mentioned we need to call the
ctors for our efi_mm, since we use apply_to_page_range() on that. Is
that only because apply_to_pte_range() tries to take the ptl for non
init_mm?

... or did I miss something else?

> The ctors allocate memory when ALLOC_SPLIT_PTLOCKS is set. Not
> calling them avoids memory leak in case we call pte_free_kernel()
> on init_mm.
> 
> Signed-off-by: Yu Zhao <yuzhao@...gle.com>

Assuming that was all, this patch makes sense to me. FWIW:

Acked-by: Mark Rutland <mark.rutland@....com>

Thanks,
Mark.

> ---
>  arch/arm64/mm/mmu.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index fa7351877af3..e8bf8a6300e8 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -370,6 +370,16 @@ static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
>  	} while (pgdp++, addr = next, addr != end);
>  }
>  
> +static phys_addr_t pgd_kernel_pgtable_alloc(int shift)
> +{
> +	void *ptr = (void *)__get_free_page(PGALLOC_GFP);
> +	BUG_ON(!ptr);
> +
> +	/* Ensure the zeroed page is visible to the page table walker */
> +	dsb(ishst);
> +	return __pa(ptr);
> +}
> +
>  static phys_addr_t pgd_pgtable_alloc(int shift)
>  {
>  	void *ptr = (void *)__get_free_page(PGALLOC_GFP);
> @@ -591,7 +601,7 @@ static int __init map_entry_trampoline(void)
>  	/* Map only the text into the trampoline page table */
>  	memset(tramp_pg_dir, 0, PGD_SIZE);
>  	__create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, PAGE_SIZE,
> -			     prot, pgd_pgtable_alloc, 0);
> +			     prot, pgd_kernel_pgtable_alloc, 0);
>  
>  	/* Map both the text and data into the kernel page table */
>  	__set_fixmap(FIX_ENTRY_TRAMP_TEXT, pa_start, prot);
> @@ -1067,7 +1077,8 @@ int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
>  		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>  
>  	__create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
> -			     size, PAGE_KERNEL, pgd_pgtable_alloc, flags);
> +			     size, PAGE_KERNEL, pgd_kernel_pgtable_alloc,
> +			     flags);
>  
>  	return __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
>  			   altmap, want_memblock);
> -- 
> 2.21.0.rc0.258.g878e2cd30e-goog
>