Commit 03792631 authored by David Woodhouse's avatar David Woodhouse Committed by Andrew Morton
Browse files

mm: implement for_each_valid_pfn() for CONFIG_SPARSEMEM 

Implement for_each_valid_pfn() based on two helper functions.

The first_valid_pfn() function largely mirrors pfn_valid(), calling into a
pfn_section_first_valid() helper which is trivial for the !VMEMMAP case,
and in the VMEMMAP case will skip to the next subsection as needed.

Since next_valid_pfn() knows that its argument *is* a valid PFN, it
doesn't need to do any checking at all while iterating over the low bits
within a (sub)section mask; the whole (sub)section is either present or
not.

Note that the VMEMMAP version of pfn_section_first_valid() may return a
value *higher* than end_pfn when skipping to the next subsection, and
first_valid_pfn() happily returns that higher value.  This is fine.

[dwmw2@infradead.org: fix next_valid_pfn() for sparsemem]
  Link: https://lkml.kernel.org/r/c15100fcf6781a60b852c4dbb43bdc98a678fcf0.camel@infradead.org
Link: https://lkml.kernel.org/r/20250423133821.789413-4-dwmw2@infradead.org


Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: default avatarMike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Ruihan Li <lrh2000@pku.edu.cn>
Cc: Will Deacon <will@kernel.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 928930c2

include/linux/mmzone.h

+78 −0
Original line number Diff line number Diff line
@@ -2075,11 +2075,37 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) 


	return usage ? test_bit(idx, usage->subsection_map) : 0;

}



static inline bool pfn_section_first_valid(struct mem_section *ms, unsigned long *pfn)

{

	struct mem_section_usage *usage = READ_ONCE(ms->usage);

	int idx = subsection_map_index(*pfn);

	unsigned long bit;



	if (!usage)

		return false;



	if (test_bit(idx, usage->subsection_map))

		return true;



	/* Find the next subsection that exists */

	bit = find_next_bit(usage->subsection_map, SUBSECTIONS_PER_SECTION, idx);

	if (bit == SUBSECTIONS_PER_SECTION)

		return false;



	*pfn = (*pfn & PAGE_SECTION_MASK) + (bit * PAGES_PER_SUBSECTION);

	return true;

}

#else

static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)

{

	return 1;

}



static inline bool pfn_section_first_valid(struct mem_section *ms, unsigned long *pfn)

{

	return true;

}

#endif



void sparse_init_early_section(int nid, struct page *map, unsigned long pnum,
@@ -2128,6 +2154,58 @@ static inline int pfn_valid(unsigned long pfn) 


	return ret;

}



/* Returns end_pfn or higher if no valid PFN remaining in range */

static inline unsigned long first_valid_pfn(unsigned long pfn, unsigned long end_pfn)

{

	unsigned long nr = pfn_to_section_nr(pfn);



	rcu_read_lock_sched();



	while (nr <= __highest_present_section_nr && pfn < end_pfn) {

		struct mem_section *ms = __pfn_to_section(pfn);



		if (valid_section(ms) &&

		    (early_section(ms) || pfn_section_first_valid(ms, &pfn))) {

			rcu_read_unlock_sched();

			return pfn;

		}



		/* Nothing left in this section? Skip to next section */

		nr++;

		pfn = section_nr_to_pfn(nr);

	}



	rcu_read_unlock_sched();

	return end_pfn;

}



static inline unsigned long next_valid_pfn(unsigned long pfn, unsigned long end_pfn)

{

	pfn++;



	if (pfn >= end_pfn)

		return end_pfn;



	/*

	 * Either every PFN within the section (or subsection for VMEMMAP) is

	 * valid, or none of them are. So there's no point repeating the check

	 * for every PFN; only call first_valid_pfn() again when crossing a

	 * (sub)section boundary (i.e. !(pfn & ~PAGE_{SUB,}SECTION_MASK)).

	 */

	if (pfn & ~(IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) ?

		   PAGE_SUBSECTION_MASK : PAGE_SECTION_MASK))

		return pfn;



	return first_valid_pfn(pfn, end_pfn);

}





#define for_each_valid_pfn(_pfn, _start_pfn, _end_pfn)			\

	for ((_pfn) = first_valid_pfn((_start_pfn), (_end_pfn));	\

	     (_pfn) < (_end_pfn);					\

	     (_pfn) = next_valid_pfn((_pfn), (_end_pfn)))



#endif



static inline int pfn_in_present_section(unsigned long pfn)