| Message ID | ae9e7d98-8a3a-cfd9-4762-bcddffdf96cf@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [next] hugetlb: pte_alloc_huge() to replace huge pte_alloc_map() | expand |
On 04/18/23 22:22, Hugh Dickins wrote: > Some architectures can have their hugetlb pages down at the lowest PTE > level: their huge_pte_alloc() using pte_alloc_map(), but without any > following pte_unmap(). Since none of these arches uses CONFIG_HIGHPTE, > this is not seen as a problem at present; but would become a problem if > forthcoming changes were to add an rcu_read_lock() into pte_offset_map(), > with the rcu_read_unlock() expected in pte_unmap(). > > Similarly in their huge_pte_offset(): pte_offset_kernel() is good enough > for that, but it's probably less confusing if we define pte_offset_huge() > along with pte_alloc_huge(). Only define them without CONFIG_HIGHPTE: > so there would be a build error to signal if ever more work is needed. > > For ease of development, define these now for 6.4-rc1, ahead of any use: > then architectures can integrate patches using them, independent from mm. > > Signed-off-by: Hugh Dickins <hughd@google.com> > --- > > include/linux/hugetlb.h | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) Hate to say that I am ignorant of the 'forthcoming changes' that might add an rcu_read_lock() into pte_offset_map(). But, the reasoning is sound and code is fine. Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
--- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -183,6 +183,23 @@ extern struct list_head huge_boot_pages; /* arch callbacks */ +#ifndef CONFIG_HIGHPTE +/* + * pte_offset_huge() and pte_alloc_huge() are helpers for those architectures + * which may go down to the lowest PTE level in their huge_pte_offset() and + * huge_pte_alloc(): to avoid reliance on pte_offset_map() without pte_unmap(). + */ +static inline pte_t *pte_offset_huge(pmd_t *pmd, unsigned long address) +{ + return pte_offset_kernel(pmd, address); +} +static inline pte_t *pte_alloc_huge(struct mm_struct *mm, pmd_t *pmd, + unsigned long address) +{ + return pte_alloc(mm, pmd) ? NULL : pte_offset_huge(pmd, address); +} +#endif + pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, unsigned long sz); /*
Some architectures can have their hugetlb pages down at the lowest PTE level: their huge_pte_alloc() using pte_alloc_map(), but without any following pte_unmap(). Since none of these arches uses CONFIG_HIGHPTE, this is not seen as a problem at present; but would become a problem if forthcoming changes were to add an rcu_read_lock() into pte_offset_map(), with the rcu_read_unlock() expected in pte_unmap(). Similarly in their huge_pte_offset(): pte_offset_kernel() is good enough for that, but it's probably less confusing if we define pte_offset_huge() along with pte_alloc_huge(). Only define them without CONFIG_HIGHPTE: so there would be a build error to signal if ever more work is needed. For ease of development, define these now for 6.4-rc1, ahead of any use: then architectures can integrate patches using them, independent from mm. Signed-off-by: Hugh Dickins <hughd@google.com> --- include/linux/hugetlb.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)