linux-kernel - Re: [PATCH v14 01/11] x86: kdump: replace the hard-coded alignment with macro CRASH

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Date:   Wed, 24 Feb 2021 14:19:42 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Chen Zhou <chenzhou10@...wei.com>
Cc:     mingo@...hat.com, tglx@...utronix.de, rppt@...nel.org,
        dyoung@...hat.com, bhe@...hat.com, will@...nel.org,
        nsaenzjulienne@...e.de, corbet@....net, John.P.donnelly@...cle.com,
        bhsharma@...hat.com, prabhakar.pkin@...il.com, horms@...ge.net.au,
        robh+dt@...nel.org, arnd@...db.de, james.morse@....com,
        xiexiuqi@...wei.com, guohanjun@...wei.com, huawei.libin@...wei.com,
        wangkefeng.wang@...wei.com, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH v14 01/11] x86: kdump: replace the hard-coded alignment
 with macro CRASH_ALIGN

On Sat, Jan 30, 2021 at 03:10:15PM +0800, Chen Zhou wrote:
> Move CRASH_ALIGN to header asm/kexec.h for later use. Besides, the
> alignment of crash kernel regions in x86 is 16M(CRASH_ALIGN), but
> function reserve_crashkernel() also used 1M alignment. So just
> replace hard-coded alignment 1M with macro CRASH_ALIGN.
[...]
> @@ -510,7 +507,7 @@ static void __init reserve_crashkernel(void)
>  	} else {
>  		unsigned long long start;
>  
> -		start = memblock_phys_alloc_range(crash_size, SZ_1M, crash_base,
> +		start = memblock_phys_alloc_range(crash_size, CRASH_ALIGN, crash_base,
>  						  crash_base + crash_size);
>  		if (start != crash_base) {
>  			pr_info("crashkernel reservation failed - memory is in use.\n");

There is a small functional change here for x86. Prior to this patch,
crash_base passed by the user on the command line is allowed to be 1MB
aligned. With this patch, such reservation will fail.

Is the current behaviour a bug in the current x86 code or it does allow
1MB-aligned reservations?

-- 
Catalin