From: kernel@jbeekman.nl (Jethro Beekman)
To: kernelnewbies@lists.kernelnewbies.org
Subject: Mapping IO memory read-write
Date: Wed, 13 Jan 2016 10:06:52 -0800 [thread overview]
Message-ID: <5696923C.80700@jbeekman.nl> (raw)
In-Reply-To: <CAK7rcp9KPD2mkKNXeT1CP1VH_ckoL5gHO=FEkTBxmQ3PCPT-Dw@mail.gmail.com>
> 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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>
prev parent reply other threads:[~2016-01-13 18:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-12 23:10 Mapping IO memory read-write Jethro Beekman
2016-01-13 14:34 ` Kenneth Adam Miller
2016-01-13 18:06 ` Jethro Beekman [this message]
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