The patch titled nommu: avoid duplicate icache flushes of shared maps has been added to the -mm tree. Its filename is nommu-avoiding-duplicate-icache-flushes-of-shared-maps.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: nommu: avoid duplicate icache flushes of shared maps From: Mike Frysinger <vapier.adi@xxxxxxxxx> When working with FDPIC, there are many shared mappings of read-only code regions between applications (the C library, applet packages like busybox, etc.), but the current do_mmap_pgoff() function will issue an icache flush whenever a VMA is added to an MM instead of only doing it when the map is initially created. The flush can instead be done when a region is first mmapped PROT_EXEC. Note that we may not rely on the first mapping of a region being executable - it's possible for it to be PROT_READ only, so we have to remember whether we've flushed the region or not, and then flush the entire region when a bit of it is made executable. However, this also affects the brk area. That will no longer be executable. We can mprotect() it to PROT_EXEC on MPU-mode kernels, but for NOMMU mode kernels, when it increases the brk allocation, making sys_brk() flush the extra from the icache should suffice. The brk area probably isn't used by NOMMU programs since the brk area can only use up the leavings from the stack allocation, where the stack allocation is larger than requested. Signed-off-by: David Howells <dhowells@xxxxxxxxxx> Signed-off-by: Mike Frysinger <vapier@xxxxxxxxxx> Cc: Jie Zhang <jie.zhang@xxxxxxxxxx> Cc: Mike Frysinger <vapier@xxxxxxxxxx> Cc: David McCullough <david_mccullough@xxxxxxxxxx> Cc: Paul Mundt <lethal@xxxxxxxxxxxx> Cc: Greg Ungerer <gerg@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mm_types.h | 2 ++ mm/nommu.c | 11 ++++++++--- 2 files changed, 10 insertions(+), 3 deletions(-) diff -puN include/linux/mm_types.h~nommu-avoiding-duplicate-icache-flushes-of-shared-maps include/linux/mm_types.h --- a/include/linux/mm_types.h~nommu-avoiding-duplicate-icache-flushes-of-shared-maps +++ a/include/linux/mm_types.h @@ -123,6 +123,8 @@ struct vm_region { struct file *vm_file; /* the backing file or NULL */ atomic_t vm_usage; /* region usage count */ + bool vm_icache_flushed : 1; /* true if the icache has been flushed for + * this region */ }; /* diff -puN mm/nommu.c~nommu-avoiding-duplicate-icache-flushes-of-shared-maps mm/nommu.c --- a/mm/nommu.c~nommu-avoiding-duplicate-icache-flushes-of-shared-maps +++ a/mm/nommu.c @@ -432,6 +432,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk) /* * Ok, looks good - let it rip. */ + flush_icache_range(mm->brk, brk); return mm->brk = brk; } @@ -1353,10 +1354,14 @@ unsigned long do_mmap_pgoff(struct file share: add_vma_to_mm(current->mm, vma); - up_write(&nommu_region_sem); + /* we flush the region from the icache only when the first executable + * mapping of it is made */ + if (vma->vm_flags & VM_EXEC && !region->vm_icache_flushed) { + flush_icache_range(region->vm_start, region->vm_end); + region->vm_icache_flushed = true; + } - if (prot & PROT_EXEC) - flush_icache_range(result, result + len); + up_write(&nommu_region_sem); kleave(" = %lx", result); return result; _ Patches currently in -mm which might be from vapier.adi@xxxxxxxxx are nommu-avoiding-duplicate-icache-flushes-of-shared-maps.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html