Re: [PATCH v3] memblock: make memblock_find_in_range method private

[Mike Rapoport]

On Tue, Aug 03, 2021 at 07:05:26PM +0100, Catalin Marinas wrote:
> 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).

It is already documented:

Documentation/admin-guide/kdump/kdump.rst:
   On arm64, use "crashkernel=Y[@X]".  Note that the start address of
   the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
 
> 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.

The doc lies :)

memblock_phys_alloc_range() boils down to 

	for_each_free_mem_range_reverse(i, nid, flags, &this_start, &this_end,
					NULL) {

		/* clamp this_{start,end} to the user defined limits */

		cand = round_down(this_end - size, align);
		if (cand >= this_start)
			return cand;
	}

-- 
Sincerely yours,
Mike.