When cramfs_physmem is used then we have the opportunity to map files directly from ROM, directly into user space, saving on RAM usage. This gives us Execute-In-Place (XIP) support. For a file to be mmap()-able, the map area has to correspond to a range of uncompressed and contiguous blocks, and in the MMU case it also has to be page aligned. A version of mkcramfs with appropriate support is necessary to create such a filesystem image. In the MMU case it may happen for a vma structure to extend beyond the actual file size. This is notably the case in binfmt_elf.c:elf_map(). Or the file's last block is shared with other files and cannot be mapped as is. Rather than refusing to mmap it, we do a "mixed" map and let the regular fault handler populate the unmapped area with RAM-backed pages. In practice the unmapped area is seldom accessed so page faults might never occur before this area is discarded. In the non-MMU case it is the get_unmapped_area method that is responsible for providing the address where the actual data can be found. No mapping is necessary of course. Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx> Tested-by: Chris Brandt <chris.brandt@xxxxxxxxxxx> --- fs/cramfs/inode.c | 194 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 194 insertions(+) diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c index 6aa1d94ed8..071ce1eb58 100644 --- a/fs/cramfs/inode.c +++ b/fs/cramfs/inode.c @@ -15,7 +15,10 @@ #include <linux/module.h> #include <linux/fs.h> +#include <linux/file.h> #include <linux/pagemap.h> +#include <linux/pfn_t.h> +#include <linux/ramfs.h> #include <linux/init.h> #include <linux/string.h> #include <linux/blkdev.h> @@ -49,6 +52,7 @@ static inline struct cramfs_sb_info *CRAMFS_SB(struct super_block *sb) static const struct super_operations cramfs_ops; static const struct inode_operations cramfs_dir_inode_operations; static const struct file_operations cramfs_directory_operations; +static const struct file_operations cramfs_physmem_fops; static const struct address_space_operations cramfs_aops; static DEFINE_MUTEX(read_mutex); @@ -96,6 +100,10 @@ static struct inode *get_cramfs_inode(struct super_block *sb, case S_IFREG: inode->i_fop = &generic_ro_fops; inode->i_data.a_ops = &cramfs_aops; + if (IS_ENABLED(CONFIG_CRAMFS_PHYSMEM) && + CRAMFS_SB(sb)->flags & CRAMFS_FLAG_EXT_BLOCK_POINTERS && + CRAMFS_SB(sb)->linear_phys_addr) + inode->i_fop = &cramfs_physmem_fops; break; case S_IFDIR: inode->i_op = &cramfs_dir_inode_operations; @@ -277,6 +285,192 @@ static void *cramfs_read(struct super_block *sb, unsigned int offset, return NULL; } +/* + * For a mapping to be possible, we need a range of uncompressed and + * contiguous blocks. Return the offset for the first block and number of + * valid blocks for which that is true, or zero otherwise. + */ +static u32 cramfs_get_block_range(struct inode *inode, u32 pgoff, u32 *pages) +{ + struct super_block *sb = inode->i_sb; + struct cramfs_sb_info *sbi = CRAMFS_SB(sb); + int i; + u32 *blockptrs, first_block_addr; + + /* + * We can dereference memory directly here as this code may be + * reached only when there is a direct filesystem image mapping + * available in memory. + */ + blockptrs = (u32 *)(sbi->linear_virt_addr + OFFSET(inode) + pgoff * 4); + first_block_addr = blockptrs[0] & ~CRAMFS_BLK_FLAGS; + i = 0; + do { + u32 block_off = i * (PAGE_SIZE >> CRAMFS_BLK_DIRECT_PTR_SHIFT); + u32 expect = (first_block_addr + block_off) | + CRAMFS_BLK_FLAG_DIRECT_PTR | + CRAMFS_BLK_FLAG_UNCOMPRESSED; + if (blockptrs[i] != expect) { + pr_debug("range: block %d/%d got %#x expects %#x\n", + pgoff+i, pgoff + *pages - 1, + blockptrs[i], expect); + if (i == 0) + return 0; + break; + } + } while (++i < *pages); + + *pages = i; + return first_block_addr << CRAMFS_BLK_DIRECT_PTR_SHIFT; +} + +#ifdef CONFIG_MMU + +static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + struct inode *inode = file_inode(file); + struct super_block *sb = inode->i_sb; + struct cramfs_sb_info *sbi = CRAMFS_SB(sb); + unsigned int pages, max_pages, offset; + unsigned long address, pgoff = vma->vm_pgoff; + char *bailout_reason; + int ret; + + if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) + return -EINVAL; + + /* Could COW work here? */ + bailout_reason = "vma is writable"; + if (vma->vm_flags & VM_WRITE) + goto bailout; + + max_pages = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT; + bailout_reason = "beyond file limit"; + if (pgoff >= max_pages) + goto bailout; + pages = min(vma_pages(vma), max_pages - pgoff); + + offset = cramfs_get_block_range(inode, pgoff, &pages); + bailout_reason = "unsuitable block layout"; + if (!offset) + goto bailout; + address = sbi->linear_phys_addr + offset; + bailout_reason = "data is not page aligned"; + if (!PAGE_ALIGNED(address)) + goto bailout; + + /* Don't map the last page if it contains some other data */ + if (unlikely(pgoff + pages == max_pages)) { + unsigned int partial = offset_in_page(inode->i_size); + if (partial) { + char *data = sbi->linear_virt_addr + offset; + data += (max_pages - 1) * PAGE_SIZE + partial; + if (memchr_inv(data, 0, PAGE_SIZE - partial) != NULL) { + pr_debug("mmap: %s: last page is shared\n", + file_dentry(file)->d_name.name); + pages--; + } + } + } + + if (!pages) { + bailout_reason = "no suitable block remaining"; + goto bailout; + } + + if (pages != vma_pages(vma)) { + /* Let's create a mixed map if we can't map it all. */ + int i; + vma->vm_flags |= VM_MIXEDMAP; + for (i = 0; i < pages; i++) { + unsigned long off = i * PAGE_SIZE; + pfn_t pfn = phys_to_pfn_t(address + off, PFN_DEV); + ret = vm_insert_mixed(vma, vma->vm_start + off, pfn); + if (ret) + return ret; + } + /* + * The normal paging machinery will take care of the + * unpopulated ptes via cramfs_readpage(). + */ + vma->vm_ops = &generic_file_vm_ops; + } else { + /* + * The entire vma is mappable. remap_pfn_range() will + * make it distinguishable from a non-direct mapping + * in /proc/<pid>/maps by substituting the file offset + * with the actual physical address. + */ + ret = remap_pfn_range(vma, vma->vm_start, address >> PAGE_SHIFT, + pages * PAGE_SIZE, vma->vm_page_prot); + if (ret) + return ret; + } + + pr_debug("mapped %s[%lu] at 0x%08lx (%u/%lu pages) to vma 0x%08lx, " + "page_prot 0x%llx\n", file_dentry(file)->d_name.name, pgoff, + address, pages, vma_pages(vma), vma->vm_start, + (unsigned long long)pgprot_val(vma->vm_page_prot)); + return 0; + +bailout: + pr_debug("%s[%lu]: direct mmap impossible: %s\n", + file_dentry(file)->d_name.name, pgoff, bailout_reason); + + /* We didn't manage a direct map, but normal paging is still possible */ + vma->vm_ops = &generic_file_vm_ops; + return 0; +} + +#else /* CONFIG_MMU */ + +static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS; +} + +static unsigned long cramfs_physmem_get_unmapped_area(struct file *file, + unsigned long addr, unsigned long len, + unsigned long pgoff, unsigned long flags) +{ + struct inode *inode = file_inode(file); + struct super_block *sb = inode->i_sb; + struct cramfs_sb_info *sbi = CRAMFS_SB(sb); + unsigned int pages, block_pages, max_pages, offset; + + pages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT; + max_pages = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT; + if (pgoff >= max_pages || pages > max_pages - pgoff) + return -EINVAL; + block_pages = pages; + offset = cramfs_get_block_range(inode, pgoff, &block_pages); + if (!offset || block_pages != pages) + return -ENOSYS; + addr = sbi->linear_phys_addr + offset; + pr_debug("get_unmapped for %s ofs %#lx siz %lu at 0x%08lx\n", + file_dentry(file)->d_name.name, pgoff*PAGE_SIZE, len, addr); + return addr; +} + +static unsigned int cramfs_physmem_mmap_capabilities(struct file *file) +{ + return NOMMU_MAP_COPY | NOMMU_MAP_DIRECT | + NOMMU_MAP_READ | NOMMU_MAP_EXEC; +} + +#endif /* CONFIG_MMU */ + +static const struct file_operations cramfs_physmem_fops = { + .llseek = generic_file_llseek, + .read_iter = generic_file_read_iter, + .splice_read = generic_file_splice_read, + .mmap = cramfs_physmem_mmap, +#ifndef CONFIG_MMU + .get_unmapped_area = cramfs_physmem_get_unmapped_area, + .mmap_capabilities = cramfs_physmem_mmap_capabilities, +#endif +}; + static void cramfs_blkdev_kill_sb(struct super_block *sb) { struct cramfs_sb_info *sbi = CRAMFS_SB(sb); -- 2.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html