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

Catalin Marinas
2021-08-04T10:02:42Z

On Tue, Aug 03, 2021 at 10:07:37PM +0300, Mike Rapoport wrote:
> 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).

Thanks for the pointer.

> > 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;
> }

Alright, it should work then. For arm64:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>