linux-kernel - Re: [PATCH] arm64/mm: Assert NR_BM_PUD_TABLES for bm

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Message-ID: <d3579c85-8cac-4e83-94a7-b6dcab72b7a1@arm.com>
Date: Wed, 7 Jan 2026 08:33:39 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Anshuman Khandual <anshuman.khandual@....com>,
 linux-arm-kernel@...ts.infradead.org
Cc: mark.rutland@....com, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/mm: Assert NR_BM_PUD_TABLES for bm_pud[]

On 07/01/2026 06:16, Anshuman Khandual wrote:
> There is an implicit assumption about bm_pud[] being single entry PUD table
> just like bp_pmd[] which is a single entry PMD table. Though only the later
> gets asserted via NR_BM_PMD_TABLES. Hence let's add a similar check for PUD
> table as well.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/arm64/mm/fixmap.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
> index c5c5425791da..e02594be8b8e 100644
> --- a/arch/arm64/mm/fixmap.c
> +++ b/arch/arm64/mm/fixmap.c
> @@ -23,8 +23,11 @@ static_assert(FIXADDR_TOT_START > PCI_IO_END);
>  	SPAN_NR_ENTRIES(FIXADDR_TOT_START, FIXADDR_TOP, PMD_SHIFT)
>  #define NR_BM_PMD_TABLES \
>  	SPAN_NR_ENTRIES(FIXADDR_TOT_START, FIXADDR_TOP, PUD_SHIFT)
> +#define NR_BM_PUD_TABLES \
> +	SPAN_NR_ENTRIES(FIXADDR_TOT_START, FIXADDR_TOP, P4D_SHIFT)
>  
>  static_assert(NR_BM_PMD_TABLES == 1);
> +static_assert(NR_BM_PUD_TABLES == 1);

But if there is only one PMD table, there must only be one PUD table (and one
P4D table, and one PGD table) by definition. So I don't think this is checking
anything that the existing PMD table check is not.

Thanks,
Ryan

>  
>  #define __BM_TABLE_IDX(addr, shift) \
>  	(((addr) >> (shift)) - (FIXADDR_TOT_START >> (shift)))