In this case, have you tried reading and writing to the memory segment being mmap'd from userland?

Here's an example mmap'ing device driver if you need to see that: https://github.com/claudioscordino/mmap_alloc

That would not have worked, but your example code did give me an idea. I was using MAP_PRIVATE while I should've been using MAP_SHARED. It works now. Thanks! Jethro On 13-01-16 06:34, Kenneth Adam Miller wrote:

In this case, have you tried reading and writing to the memory segment being mmap'd from userland?

Here's an example mmap'ing device driver if you need to see that: https://github.com/claudioscordino/mmap_alloc

On Tue, Jan 12, 2016 at 6:10 PM, Jethro Beekman <kernel@jbeekman.nl <mailto:kernel@jbeekman.nl>> wrote:

I'm writing a device driver for a memory-mapped device on x86-64. I'm mapping the device in the kernel using ioremap_cache(). My file_operations.mmap function is as follows:

static int dev_mmap(struct file *filep, struct vm_area_struct *vma) { vma->vm_page_prot.pgprot|=_PAGE_BIT_RW; return vm_iomap_memory(vma,START,LEN); }

The user process calls mmap(..,PROT_READ|PROT_WRITE|PROT_EXEC,..). The mapping in /proc/[pid]/maps shows the write bit. However, when looking at the actual page table entry does not have the RW bit set. For example:

virtual address = 0000_0001_8000_0000 cr3 = 0000_0000_700a_e000 phys:0000_0000_700a_e000 = 0000_0000_7e05_5067 (P|RW|US|A|D) phys:0000_0000_7e05_5030 = 0000_0001_66e2_9067 (P|RW|US|A|D) phys:0000_0001_66e2_9000 = 0000_0001_69db_3067 (P|RW|US|A|D) phys:0000_0001_69db_3000 = 0000_0000_8020_0225 (P|US|A|SOFTW1)

Am I doing something wrong?

Jethro

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