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mm/vmalloc: Gracefully unmap huge ptes 

Commit f7ee1f13d6 ("mm/vmalloc: enable mapping of huge pages at pte
level in vmap") added its support by reusing the set_huge_pte_at() API,
which is otherwise only used for user mappings. But when unmapping those
huge ptes, it continued to call ptep_get_and_clear(), which is a
layering violation. To date, the only arch to implement this support is
powerpc and it all happens to work ok for it.

But arm64's implementation of ptep_get_and_clear() can not be safely
used to clear a previous set_huge_pte_at(). So let's introduce a new
arch opt-in function, arch_vmap_pte_range_unmap_size(), which can
provide the size of a (present) pte. Then we can call
huge_ptep_get_and_clear() to tear it down properly.

Note that if vunmap_range() is called with a range that starts in the
middle of a huge pte-mapped page, we must unmap the entire huge page so
the behaviour is consistent with pmd and pud block mappings. In this
case emit a warning just like we do for pmd/pud mappings.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: Luiz Capitulino <luizcap@redhat.com>
Link: https://lore.kernel.org/r/20250422081822.1836315-9-ryan.roberts@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
pull/1112/head
Ryan Roberts 2025-04-22 09:18:16 +01:00 committed by Will Deacon
parent 61ef8ddaa3
commit 2fba13371f
2 changed files with 24 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/vmalloc.h
View File

@ -113,6 +113,14 @@ static inline unsigned long arch_vmap_pte_range_map_size(unsigned long addr, uns
}
#endif
#ifndef arch_vmap_pte_range_unmap_size
static inline unsigned long arch_vmap_pte_range_unmap_size(unsigned long addr,
pte_t *ptep)
{
return PAGE_SIZE;
}
#endif
#ifndef arch_vmap_pte_supported_shift
static inline int arch_vmap_pte_supported_shift(unsigned long size)
{

18
mm/vmalloc.c
View File

@ -350,12 +350,26 @@ static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
pgtbl_mod_mask *mask)
{
pte_t *pte;
pte_t ptent;
unsigned long size = PAGE_SIZE;
pte = pte_offset_kernel(pmd, addr);
do {
pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte);
#ifdef CONFIG_HUGETLB_PAGE
size = arch_vmap_pte_range_unmap_size(addr, pte);
if (size != PAGE_SIZE) {
if (WARN_ON(!IS_ALIGNED(addr, size))) {
addr = ALIGN_DOWN(addr, size);
pte = PTR_ALIGN_DOWN(pte, sizeof(*pte) * (size >> PAGE_SHIFT));
}
ptent = huge_ptep_get_and_clear(&init_mm, addr, pte, size);
if (WARN_ON(end - addr < size))
size = end - addr;
} else
#endif
ptent = ptep_get_and_clear(&init_mm, addr, pte);
WARN_ON(!pte_none(ptent) && !pte_present(ptent));
} while (pte++, addr += PAGE_SIZE, addr != end);
} while (pte += (size >> PAGE_SHIFT), addr += size, addr != end);
*mask |= PGTBL_PTE_MODIFIED;
}