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mm/memremap.c: take a pgmap reference on page allocation

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ZONE_DEVICE pages have a struct dev_pagemap which is allocated by a
driver.  When the struct page is first allocated by the kernel in
memremap_pages() a reference is taken on the associated pagemap to ensure
it is not freed prior to the pages being freed.

Prior to 27674ef6c7 ("mm: remove the extra ZONE_DEVICE struct page
refcount") pages were considered free and returned to the driver when the
reference count dropped to one.  However the pagemap reference was not
dropped until the page reference count hit zero.  This would occur as part
of the final put_page() in memunmap_pages() which would wait for all pages
to be freed prior to returning.

When the extra refcount was removed the pagemap reference was no longer
being dropped in put_page().  Instead memunmap_pages() was changed to
explicitly drop the pagemap references.  This means that memunmap_pages()
can complete even though pages are still mapped by the kernel which can
lead to kernel crashes, particularly if a driver frees the pagemap.

To fix this drivers should take a pagemap reference when allocating the
page.  This reference can then be returned when the page is freed.

Link: https://lkml.kernel.org/r/12d155ec727935ebfbb4d639a03ab374917ea51b.1664366292.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Fixes: 27674ef6c7 ("mm: remove the extra ZONE_DEVICE struct page refcount")
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Alex Sierra <alex.sierra@amd.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>

Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Alistair Popple 2022-09-28 22:01:17 +10:00 committed by Andrew Morton
parent ef23345089
commit 0dc45ca1ce
1 changed files with 19 additions and 6 deletions
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25
mm/memremap.c
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@ -138,8 +138,11 @@ void memunmap_pages(struct dev_pagemap *pgmap)
int i;
percpu_ref_kill(&pgmap->ref);
for (i = 0; i < pgmap->nr_range; i++)
percpu_ref_put_many(&pgmap->ref, pfn_len(pgmap, i));
if (pgmap->type != MEMORY_DEVICE_PRIVATE &&
pgmap->type != MEMORY_DEVICE_COHERENT)
for (i = 0; i < pgmap->nr_range; i++)
percpu_ref_put_many(&pgmap->ref, pfn_len(pgmap, i));
wait_for_completion(&pgmap->done);
for (i = 0; i < pgmap->nr_range; i++)
@ -264,7 +267,9 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
memmap_init_zone_device(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
PHYS_PFN(range->start),
PHYS_PFN(range_len(range)), pgmap);
percpu_ref_get_many(&pgmap->ref, pfn_len(pgmap, range_id));
if (pgmap->type != MEMORY_DEVICE_PRIVATE &&
pgmap->type != MEMORY_DEVICE_COHERENT)
percpu_ref_get_many(&pgmap->ref, pfn_len(pgmap, range_id));
return 0;
err_add_memory:
@ -502,16 +507,24 @@ void free_zone_device_page(struct page *page)
page->mapping = NULL;
page->pgmap->ops->page_free(page);
/*
* Reset the page count to 1 to prepare for handing out the page again.
*/
if (page->pgmap->type != MEMORY_DEVICE_PRIVATE &&
page->pgmap->type != MEMORY_DEVICE_COHERENT)
/*
* Reset the page count to 1 to prepare for handing out the page
* again.
*/
set_page_count(page, 1);
else
put_dev_pagemap(page->pgmap);
}
void zone_device_page_init(struct page *page)
{
/*
* Drivers shouldn't be allocating pages after calling
* memunmap_pages().
*/
WARN_ON_ONCE(!percpu_ref_tryget_live(&page->pgmap->ref));
set_page_count(page, 1);
lock_page(page);
}