From: slash.tmp@free•fr (Mason)
To: linux-arm-kernel@lists•infradead.org
Subject: Unhandled fault: page domain fault (0x81b) at 0x00e41008
Date: Sat, 23 Jan 2016 23:46:06 +0100 [thread overview]
Message-ID: <56A402AE.6070503@free.fr> (raw)
In-Reply-To: <56A3E84A.1000604@free.fr>
On 23/01/2016 21:53, Mason wrote:
> But I would consider mmaping /dev/mem even simpler: it doesn't
> require writing a single line of kernel code, and it works as
> expected. The gist of the code is:
>
> fd = open("/path/to/file", O_RDONLY);
> mem_fd = open("/dev/mem", O_WRONLY | O_SYNC);
> va = mmap(NULL, len, PROT_WRITE, MAP_SHARED, mem_fd, phys_addr);
> read(fd, va, len);
>
> And that's it. If I understand correctly, the mem driver
> will copy the file contents directly to "remote" RAM.
>
> Is there something wrong with this solution, in your opinion?
For my own reference, Arnd had several comments:
> /dev/mem is deprecated and often gets disabled because it is a
> security hole. Your driver can implement its own mmap function
> if needed.
>
> On the user space side, you have to be careful to use aligned
> accesses on device memory, you can't just memcpy into a buffer
> from mmap()
>
> /dev/mem maps memory as MT_DEVICE, which has stricter rules
> [than ordinary RAM]. If you want an mmap of this memory, you
> should really implement your own with the correct attributes.
>
> read may or may not do unaligned accesses, depending on a lot of
> factors like compiler optimization flags when building the kernel
next prev parent reply other threads:[~2016-01-23 22:46 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-22 17:37 Unhandled fault: page domain fault (0x81b) at 0x00e41008 Mason
2016-01-22 17:48 ` Russell King - ARM Linux
2016-01-22 18:59 ` Mason
2016-01-22 19:34 ` Russell King - ARM Linux
2016-01-22 23:15 ` Mason
2016-01-22 23:57 ` Russell King - ARM Linux
2016-01-23 11:14 ` Mason
2016-01-23 11:34 ` Russell King - ARM Linux
2016-01-23 20:53 ` Mason
2016-01-23 22:46 ` Mason [this message]
2016-01-23 23:59 ` Russell King - ARM Linux
2016-01-24 13:27 ` Mason
2016-01-27 10:36 ` Mason
2016-01-27 10:48 ` Russell King - ARM Linux
2016-01-27 12:04 ` Mason
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