linux-kernel - Re: [PATCH v3 07/60] arm64: ptdump: Discover start of vmemmap region at runtime

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Message-ID: <e26236c5-d4ea-caf3-eeee-5c88a6814ea4@arm.com>
Date:   Tue, 7 Mar 2023 16:36:16 +0000
From:   Ryan Roberts <ryan.roberts@....com>
To:     Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v3 07/60] arm64: ptdump: Discover start of vmemmap region
 at runtime

On 07/03/2023 14:04, Ard Biesheuvel wrote:
> We will soon reclaim the part of the vmemmap region that covers VA space
> that is not addressable by the hardware. To avoid confusion, ensure that
> the 'vmemmap start' marker points at the start of the region that is
> actually being used for the struct page array, rather than the start of
> the region we set aside for it at build time.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  arch/arm64/mm/ptdump.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
> index 910b35f02280cbdb..8f37d6d8b5216473 100644
> --- a/arch/arm64/mm/ptdump.c
> +++ b/arch/arm64/mm/ptdump.c
> @@ -37,6 +37,7 @@ enum address_markers_idx {
>  	MODULES_END_NR,
>  	VMALLOC_START_NR,
>  	VMALLOC_END_NR,
> +	VMEMMAP_START_NR,
>  };
>  
>  static struct addr_marker address_markers[] = {
> @@ -386,6 +387,10 @@ static int __init ptdump_init(void)
>  #endif
>  	address_markers[VMALLOC_END_NR].start_address = VMALLOC_END;
>  	ptdump_initialize();
> +	if (vabits_actual < VA_BITS) {
> +		address_markers[VMEMMAP_START_NR].start_address =
> +			(unsigned long)virt_to_page(_PAGE_OFFSET(vabits_actual));
> +	}

nit: Do you need the conditional here? Why not just do it unconditionally?

>  	ptdump_debugfs_register(&kernel_ptdump_info, "kernel_page_tables");
>  	return 0;
>  }