linux-ext4 - Re: riscv32 EXT4 splat, 6.8 regression?

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Date: Tue, 16 Apr 2024 20:05:38 +0200
From: Björn Töpel <bjorn@...nel.org>
To: Nam Cao <namcao@...utronix.de>
Cc: Mike Rapoport <rppt@...nel.org>, Christian Brauner <brauner@...nel.org>,
 Andreas Dilger <adilger@...ger.ca>, Al Viro <viro@...iv.linux.org.uk>,
 linux-fsdevel <linux-fsdevel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 linux-riscv@...ts.infradead.org, Theodore Ts'o <tytso@....edu>, Ext4
 Developers List <linux-ext4@...r.kernel.org>, Conor Dooley
 <conor@...nel.org>, "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Anders
 Roxell <anders.roxell@...aro.org>, Alexandre Ghiti <alex@...ti.fr>
Subject: Re: riscv32 EXT4 splat, 6.8 regression?

Nam Cao <namcao@...utronix.de> writes:

> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index fa34cf55037b..f600cfee0aef 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -197,7 +197,6 @@ early_param("mem", early_mem);
>  static void __init setup_bootmem(void)
>  {
>  	phys_addr_t vmlinux_end = __pa_symbol(&_end);
> -	phys_addr_t max_mapped_addr;
>  	phys_addr_t phys_ram_end, vmlinux_start;
>  
>  	if (IS_ENABLED(CONFIG_XIP_KERNEL))
> @@ -238,17 +237,9 @@ static void __init setup_bootmem(void)
>  	/*
>  	 * memblock allocator is not aware of the fact that last 4K bytes of
>  	 * the addressable memory can not be mapped because of IS_ERR_VALUE
> -	 * macro. Make sure that last 4k bytes are not usable by memblock
> -	 * if end of dram is equal to maximum addressable memory.  For 64-bit
> -	 * kernel, this problem can't happen here as the end of the virtual
> -	 * address space is occupied by the kernel mapping then this check must
> -	 * be done as soon as the kernel mapping base address is determined.
> +	 * macro. Make sure that last 4k bytes are not usable by memblock.
>  	 */
> -	if (!IS_ENABLED(CONFIG_64BIT)) {
> -		max_mapped_addr = __pa(~(ulong)0);
> -		if (max_mapped_addr == (phys_ram_end - 1))
> -			memblock_set_current_limit(max_mapped_addr - 4096);
> -	}
> +	memblock_reserve(__pa(-PAGE_SIZE), PAGE_SIZE);
>  
>  	min_low_pfn = PFN_UP(phys_ram_base);
>  	max_low_pfn = max_pfn = PFN_DOWN(phys_ram_end);

Nice! Would you mind submitting this as a proper fix (unless there's a
way to do it non-arch specific like Matthew pointed out).

Björn