On 28.05.25 12:44, David Hildenbrand wrote:
On 28.05.25 12:34, Ryan Roberts wrote:
Hi David,
On 09/05/2025 16:30, David Hildenbrand wrote:
Let's test some basic functionality using /dev/mem. These tests will
implicitly cover some PAT (Page Attribute Handling) handling on x86.
These tests will only run when /dev/mem access to the first two pages
in physical address space is possible and allowed; otherwise, the tests
are skipped.
We are seeing really horrible RAS errors with this test when run on arm64 tx2
machine. Based solely on reviewing the code, I think the problem is that tx2
doesn't have anything at phys address 0, so test_read_access() is trying to put
trasactions out to a bad address on the bus.
tx2 /proc/iomem:
$ sudo cat /proc/iomem
30000000-37ffffff : PCI ECAM
38000000-3fffffff : PCI ECAM
40000000-5fffffff : PCI Bus 0000:00
...
Whereas my x86 box has some reserved memory:
$ sudo cat /proc/iomem
00000000-00000fff : Reserved
00001000-0003dfff : System RAM
...
A quick fix would be to make this test specific to x86 (the only one I
tested on). We should always have the lower two pages IIRC (BIOS stuff etc).
I think perhaps the only safe way to handle this is to parse /proc/iomem for a
region of "System RAM" that is at least 2 pages then use that for your read
tests. This would also solve the hypothetical issue of reading something that
has read size effects.
That sounds also plausible yes. I somehow remembered that mmap() would
fail if "there is nothing".
Ah, my memory comes back, we perform checks only with CONFIG_STRICT_DEVMEM.
--
Cheers,
David / dhildenb
