linux-kernel - Re: [PATCH v3] memblock: make memblock_find_in

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Date:   Tue, 3 Aug 2021 19:05:26 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Frank Rowand <frowand.list@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Len Brown <lenb@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>, devicetree@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-mm@...ck.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v3] memblock: make memblock_find_in_range method private

On Tue, Aug 03, 2021 at 09:42:18AM +0300, Mike Rapoport wrote:
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 8490ed2917ff..0bffd2d1854f 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -74,6 +74,7 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>  static void __init reserve_crashkernel(void)
>  {
>  	unsigned long long crash_base, crash_size;
> +	unsigned long long crash_max = arm64_dma_phys_limit;
>  	int ret;
>  
>  	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> @@ -84,33 +85,18 @@ static void __init reserve_crashkernel(void)
>  
>  	crash_size = PAGE_ALIGN(crash_size);
>  
> -	if (crash_base == 0) {
> -		/* Current arm64 boot protocol requires 2MB alignment */
> -		crash_base = memblock_find_in_range(0, arm64_dma_phys_limit,
> -				crash_size, SZ_2M);
> -		if (crash_base == 0) {
> -			pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
> -				crash_size);
> -			return;
> -		}
> -	} else {
> -		/* User specifies base address explicitly. */
> -		if (!memblock_is_region_memory(crash_base, crash_size)) {
> -			pr_warn("cannot reserve crashkernel: region is not memory\n");
> -			return;
> -		}
> +	/* User specifies base address explicitly. */
> +	if (crash_base)
> +		crash_max = crash_base + crash_size;
>  
> -		if (memblock_is_region_reserved(crash_base, crash_size)) {
> -			pr_warn("cannot reserve crashkernel: region overlaps reserved memory\n");
> -			return;
> -		}
> -
> -		if (!IS_ALIGNED(crash_base, SZ_2M)) {
> -			pr_warn("cannot reserve crashkernel: base address is not 2MB aligned\n");
> -			return;
> -		}
> +	/* Current arm64 boot protocol requires 2MB alignment */
> +	crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
> +					       crash_base, crash_max);
> +	if (!crash_base) {
> +		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
> +			crash_size);
> +		return;
>  	}
> -	memblock_reserve(crash_base, crash_size);

We'll miss a bit on debug information provided to the user in case of a
wrong crash_base/size option on the command line. Not sure we care much,
though the alignment would probably be useful (maybe we document it
somewhere).

What I haven't checked is whether memblock_phys_alloc_range() aims to
get a 2MB aligned end (size) as well. If crash_size is not 2MB aligned,
crash_max wouldn't be either and the above could fail. We only care
about the crash_base to be aligned but the memblock_phys_alloc_range()
doc says that both the start and size would be aligned to this.

-- 
Catalin