This function provides the anonymous equivalent of linear_page_index(), instead offsetting based on the anonymous page offset of the VMA.
It is valid only for anonymous or MAP_PRIVATE file-backed mappings, in other words CoW mappings. For pure anon VMAs, this will be equal to linear_page_index(). Assert that both of these invariants are true In linear_anon_page_index() and implement the algorithm in __linear_anon_page_index(). Note that MAP_PRIVATE-/dev/zero mappings will satisfy vma_is_anonymous() but not fulfill this invariant, so when asserting this we check vma->vm_file to account for this. We do not update callsites yet, so no functional change intended. Also const-ify vma_is_anonymous() to make it compatible with the const-ified linear_anon_page_index(). While we're here, update linear_page_index() to be more succinct. VMA userland tests are also updated accordingly. Reviewed-by: Gregory Price (Meta) <[email protected]> Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]> --- include/linux/mm.h | 2 +- include/linux/pagemap.h | 40 +++++++++++++++++++++++++++++++++++++--- tools/testing/vma/include/dup.h | 25 ++++++++++++++++++++++++- 3 files changed, 62 insertions(+), 5 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index a3368c542947..da36a6cc907c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1556,7 +1556,7 @@ static inline void vma_desc_set_anonymous(struct vm_area_desc *desc) desc->vm_ops = NULL; } -static inline bool vma_is_anonymous(struct vm_area_struct *vma) +static inline bool vma_is_anonymous(const struct vm_area_struct *vma) { return !vma->vm_ops; } diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index c6fc783aaee5..0adfa6605653 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -1094,10 +1094,44 @@ static inline pgoff_t linear_page_delta(const struct vm_area_struct *vma, static inline pgoff_t linear_page_index(const struct vm_area_struct *vma, const unsigned long address) { - pgoff_t pgoff; + return linear_page_delta(vma, address) + vma_start_pgoff(vma); +} + +static inline pgoff_t __linear_anon_page_index(const struct vm_area_struct *vma, + const unsigned long address) +{ + return linear_page_delta(vma, address) + vma_start_anon_pgoff(vma); +} + +/** + * linear_anon_page_index() - Determine the absolute anonymous page offset of + * @address within @vma. + * @vma: An anonymous or MAP_PRIVATE file-backed VMA in which @address resides. + * @address: The address whose absolute page offset is required. + * + * This returns the anonymous page offset of @address, which is the page offset + * the address possessed at the time the VMA was first faulted. + * + * For anonymous mappings, this returns the same value as linear_page_index(). + * + * For MAP_PRIVATE file-backed mappings, this returns the anonymous page offset + * of @address, which is the page offset the address possessed at the time the + * VMA was first faulted. + * + * It is not valid to call this function for shared file-backed mappings. + * + * Returns: The absolute anonymous page offset of @address within @vma. + */ +static inline pgoff_t linear_anon_page_index(const struct vm_area_struct *vma, + const unsigned long address) +{ + const pgoff_t pgoff = __linear_anon_page_index(vma, address); + + VM_WARN_ON_ONCE(!vma_is_cow_mapping(vma)); + /* Account for MAP_PRIVATE-/dev/zero which is only semi-anonymous. */ + if (vma_is_anonymous(vma) && !vma->vm_file) + VM_WARN_ON_ONCE(pgoff != linear_page_index(vma, address)); - pgoff = linear_page_delta(vma, address); - pgoff += vma_start_pgoff(vma); return pgoff; } diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index 40ad83936b28..4c58487b764e 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -1428,7 +1428,7 @@ static inline void vma_iter_set(struct vma_iterator *vmi, unsigned long addr) mas_set(&vmi->mas, addr); } -static inline bool vma_is_anonymous(struct vm_area_struct *vma) +static inline bool vma_is_anonymous(const struct vm_area_struct *vma) { return !vma->vm_ops; } @@ -1621,3 +1621,26 @@ static inline pgprot_t vma_get_page_prot(const struct vm_area_struct *vma) { return vma_flags_to_page_prot(vma->flags); } + +static inline pgoff_t __linear_anon_page_index(const struct vm_area_struct *vma, + const unsigned long address) +{ + pgoff_t pgoff; + + pgoff = linear_page_delta(vma, address); + pgoff += vma_start_anon_pgoff(vma); + return pgoff; +} + +static inline pgoff_t linear_anon_page_index(const struct vm_area_struct *vma, + const unsigned long address) +{ + const pgoff_t pgoff = __linear_anon_page_index(vma, address); + + VM_WARN_ON_ONCE(!vma_is_cow_mapping(vma)); + /* Account for MAP_PRIVATE-/dev/zero which is only semi-anonymous. */ + if (vma_is_anonymous(vma) && !vma->vm_file) + VM_WARN_ON_ONCE(pgoff != linear_page_index(vma, address)); + + return pgoff; +} -- 2.55.0
