Commit 8d400913 authored by Oscar Salvador's avatar Oscar Salvador Committed by Linus Torvalds
Browse files

x86/vmemmap: handle unpopulated sub-pmd ranges 

When sizeof(struct page) is not a power of 2, sections do not span a PMD
anymore and so when populating them some parts of the PMD will remain
unused.

Because of this, PMDs will be left behind when depopulating sections since
remove_pmd_table() thinks that those unused parts are still in use.

Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv()
will do the right thing and will let us free the PMD when the last user of
it is gone.

This patch is based on a similar patch by David Hildenbrand:

https://lore.kernel.org/linux-mm/20200722094558.9828-9-david@redhat.com/

[osalvador@suse.de: go back to the ifdef version]
  Link: https://lkml.kernel.org/r/YGy++mSft7K4u+88@localhost.localdomain

Link: https://lkml.kernel.org/r/20210309214050.4674-4-osalvador@suse.de


Signed-off-by: default avatarOscar Salvador <osalvador@suse.de>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 69ccfe74

arch/x86/mm/init_64.c

+55 −13
Original line number Diff line number Diff line
@@ -826,6 +826,51 @@ void __init paging_init(void) 
	zone_sizes_init();

}



#ifdef CONFIG_SPARSEMEM_VMEMMAP

#define PAGE_UNUSED 0xFD



/* Returns true if the PMD is completely unused and thus it can be freed */

static bool __meminit vmemmap_pmd_is_unused(unsigned long addr, unsigned long end)

{

	unsigned long start = ALIGN_DOWN(addr, PMD_SIZE);



	memset((void *)addr, PAGE_UNUSED, end - addr);



	return !memchr_inv((void *)start, PAGE_UNUSED, PMD_SIZE);

}



static void __meminit vmemmap_use_sub_pmd(unsigned long start)

{

	/*

	 * As we expect to add in the same granularity as we remove, it's

	 * sufficient to mark only some piece used to block the memmap page from

	 * getting removed when removing some other adjacent memmap (just in

	 * case the first memmap never gets initialized e.g., because the memory

	 * block never gets onlined).

	 */

	memset((void *)start, 0, sizeof(struct page));

}



static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end)

{

	/*

	 * Could be our memmap page is filled with PAGE_UNUSED already from a

	 * previous remove. Make sure to reset it.

	 */

	vmemmap_use_sub_pmd(start);



	/*

	 * Mark with PAGE_UNUSED the unused parts of the new memmap range

	 */

	if (!IS_ALIGNED(start, PMD_SIZE))

		memset((void *)start, PAGE_UNUSED,

		        start - ALIGN_DOWN(start, PMD_SIZE));

	if (!IS_ALIGNED(end, PMD_SIZE))

		memset((void *)end, PAGE_UNUSED,

		        ALIGN(end, PMD_SIZE) - end);

}

#endif



/*

 * Memory hotplug specific functions

 */
@@ -871,8 +916,6 @@ int arch_add_memory(int nid, u64 start, u64 size, 
	return add_pages(nid, start_pfn, nr_pages, params);

}



#define PAGE_INUSE 0xFD



static void __meminit free_pagetable(struct page *page, int order)

{

	unsigned long magic;
@@ -1006,7 +1049,6 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end, 
	unsigned long next, pages = 0;

	pte_t *pte_base;

	pmd_t *pmd;

	void *page_addr;



	pmd = pmd_start + pmd_index(addr);

	for (; addr < end; addr = next, pmd++) {
@@ -1026,22 +1068,16 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end, 
				pmd_clear(pmd);

				spin_unlock(&init_mm.page_table_lock);

				pages++;

			} else {

				/* If here, we are freeing vmemmap pages. */

				memset((void *)addr, PAGE_INUSE, next - addr);



				page_addr = page_address(pmd_page(*pmd));

				if (!memchr_inv(page_addr, PAGE_INUSE,

						PMD_SIZE)) {

			}

#ifdef CONFIG_SPARSEMEM_VMEMMAP

			else if (vmemmap_pmd_is_unused(addr, next)) {

					free_hugepage_table(pmd_page(*pmd),

							    altmap);



					spin_lock(&init_mm.page_table_lock);

					pmd_clear(pmd);

					spin_unlock(&init_mm.page_table_lock);

			}

			}



#endif

			continue;

		}
@@ -1492,11 +1528,17 @@ static int __meminit vmemmap_populate_hugepages(unsigned long start, 


				addr_end = addr + PMD_SIZE;

				p_end = p + PMD_SIZE;



				if (!IS_ALIGNED(addr, PMD_SIZE) ||

				    !IS_ALIGNED(next, PMD_SIZE))

					vmemmap_use_new_sub_pmd(addr, next);



				continue;

			} else if (altmap)

				return -ENOMEM; /* no fallback */

		} else if (pmd_large(*pmd)) {

			vmemmap_verify((pte_t *)pmd, node, addr, next);

			vmemmap_use_sub_pmd(addr);

			continue;

		}

		if (vmemmap_populate_basepages(addr, next, node, NULL))