I was auding the /dev/mem code for more questionable uses of __pa(), and ran across this. My assumption is that if you use /dev/kmem, you expect to be able to read the kernel virtual mappings. However, those mappings _stop_ as soon as we hit high memory. The pfn_valid() check in here is good for memory holes, but since highmem pages are still valid, it does no good for those. Also, since we are now checking that __pa() is being done on valid virtual addresses, this might have tripped the new check. Even with the new check, this code would have been broken with the NUMA remapping code had we not ripped it out: https://patchwork.kernel.org/patch/2075911/ Signed-off-by: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> --- linux-2.6.git-dave/drivers/char/mem.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff -puN drivers/char/mem.c~make-kmem-return-error-for-highmem drivers/char/mem.c --- linux-2.6.git/drivers/char/mem.c~make-kmem-return-error-for-highmem 2013-02-08 12:27:57.033770045 -0800 +++ linux-2.6.git-dave/drivers/char/mem.c 2013-02-08 12:27:57.041770125 -0800 @@ -337,10 +337,19 @@ static int mmap_mem(struct file *file, s #ifdef CONFIG_DEVKMEM static int mmap_kmem(struct file *file, struct vm_area_struct *vma) { + unsigned long kernel_vaddr; unsigned long pfn; + kernel_vaddr = (u64)vma->vm_pgoff << PAGE_SHIFT; + /* + * pfn_valid() (below) does not trip for highmem addresses. This + * essentially means that we will be mapping gibberish in for them + * instead of what the _kernel_ has mapped at the requested address. + */ + if (kernel_vaddr >= high_memory) + return -EIO; /* Turn a kernel-virtual address into a physical page frame */ - pfn = __pa((u64)vma->vm_pgoff << PAGE_SHIFT) >> PAGE_SHIFT; + pfn = __pa(kernel_vaddr) >> PAGE_SHIFT; /* * RED-PEN: on some architectures there is more mapped memory than diff -puN mm/nommu.c~make-kmem-return-error-for-highmem mm/nommu.c _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>