Re: [PATCH 5/5] kexec: X86: Pass memory ranges via e820 table instead of memmap= boot parameter

[H. Peter Anvin]

Yes... That is one reason I think it is a real problem.


Dave Hansen <dave@xxxxxxxx> wrote:

>On 04/12/2013 07:56 AM, H. Peter Anvin wrote:
>> On 04/12/2013 07:31 AM, Vivek Goyal wrote:
>>>> I also have to admit that I don't see the difference between
>/dev/mem
>>>> and /dev/oldmem, as the former allows access to memory ranges
>outside
>>>> the ones used by the current kernel, which is what the oldmem
>device
>>>> seems to be intended to od.
>
>It varies from arch to arch of course.
>
>But, /dev/mem has restrictions on it, like CONFIG_STRICT_DEVMEM or the
>ARCH_HAS_VALID_PHYS_ADDR_RANGE.  There's a lot of stuff that depends on
>it, *and* folks have tried to fix it up so that it's not _as_ blatant
>of
>a way to completely screw your system.
>
>/dev/mem also tries to be nice to arches that have restrictions like:
>
>>                         /*
>>                          * On ia64 if a page has been mapped
>somewhere as
>>                          * uncached, then it must also be accessed
>uncached
>>                          * by the kernel or data corruption may occur
>>                          */
>
>I think /dev/oldmem isn't so nice and could actually cause some real
>problems if used on ia64 where the cached/uncached accesses are mixed.

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