On 01/03/17 at 01:15pm, Dave Jiang wrote:
On 01/03/2017 11:24 AM, Dan Williams wrote:
> On Tue, Jan 3, 2017 at 12:31 AM, Baoquan He <bhe(a)redhat.com> wrote:
>> Hi Dan,
>> On 11/22/16 at 09:26am, Dan Williams wrote:
>>> [ replying for Dave since he's offline today and tomorrow ]
>>> On Tue, Nov 22, 2016 at 12:47 AM, Ingo Molnar <mingo(a)kernel.org>
>>>> * Dave Jiang <dave.jiang(a)intel.com> wrote:
>>>>> CONFIG_RANDOMIZE_BASE relocates the kernel to a random base
>>>>> However it does not take into account the memmap= parameter passed
>>>>> the kernel commandline.
>>>> memmap= parameters are often used as a list.
>>>>> [...] This results in the kernel sometimes being put in the middle
of the user
>>>>> memmap. [...]
>>>> What does this mean? If memmap= is used to re-define the memory map then
>>>> kernel getting in the middle of a RAM area is what we want, isn't
it? What we
>>>> don't want is for the kernel to get into reserved areas, right?
>>> Right, this is about teaching kaslr to not land the kernel in newly
>>> defined reserved regions that were not marked reserved in the initial
>>> e820 map from platform firmware.
>> If only tell kaslr to not land kernel in newly defined reserved regions,
>> memory added by "memmap=nn[KMG]@ss[KMG]" should not be avoided since
>> it's usable memory. Kernel randomized into this region is also what we
>> want. Not sure if I understand it right.
> You're right, this is supposed to be for memmap=nn!ss cases which
> defines reserved persistent memory ranges, not memmap=nn@ss which
> defines usable memory.
> We need to fix mem_avoid_memmap() to only skip memmap= statements that
> specify reserved memory.
Thanks for confirmation, Dan!
I think nn@ss is the only one that we should skip over, otherwise
everything else looks like should be avoided. I'll update.
I guess your purpose is to avoid the user defined reserved memory and
pmem which I am not very sure about since kaslr won't stamp on ACPI
region reported by BIOS. Seems OK to avoid them all except of nn@ss.
I have other concerns, will directly comment in your v4 post.