Hi Steve,
Thanks for the v2. I still did not get much time to go through this in
deep and have a go with the same on LVA supporting prototype platforms
or old CPUs (which don't support ARMv8.2 LVA/LPA extensions) I have. May
be I will give this a quick check on the same in a day or two.
On 05/28/2019 09:40 PM, Steve Capper wrote:
This patch series adds support for 52-bit kernel VAs using some of the
machinery already introduced by the 52-bit userspace VA code in 5.0.
As 52-bit virtual address support is an optional hardware feature,
software support for 52-bit kernel VAs needs to be deduced at early boot
time. If HW support is not available, the kernel falls back to 48-bit.
A significant proportion of this series focuses on "de-constifying"
VA_BITS related constants.
In order to allow for a KASAN shadow that changes size at boot time, one
must fix the KASAN_SHADOW_END for both 48 & 52-bit VAs and "grow" the
start address. Also, it is highly desirable to maintain the same
function addresses in the kernel .text between VA sizes. Both of these
requirements necessitate us to flip the kernel address space halves s.t.
the direct linear map occupies the lower addresses.
In V2 of this series (apologies for the long delay from V1), the major
change is that PAGE_OFFSET is retained as a constant. This allows for
much faster virt_to_page computations. This is achieved by expanding the
size of the VMEMMAP region to accommodate a disjoint 52-bit/48-bit
direct linear map. This has been found to work well in my testing, but I
would appreciate any feedback on this if it needs changing. To aid with
git bisect, this logic is broken down into a few smaller patches.
As far as I'm aware, there are two outstanding issues with this series
that need to be resolved:
1) Is the code patching for ttbr1_offset safe? I need to analyse this
a little more,
2) How can this memory map be advertised to kdump tools/documentation?
I was planning on getting the kernel VA structure agreed on, then I
would add the relevant exports/documentation.
Indeed, in the absence of corresponding changes to the Documentation
section,
it is hard to visualize the changes being made in the memory map.
Also I would suggest that we note in the patchset itself (may be the git
log) that kdump tools (or even crash for that matter) will be broken
with this patchset - to prevent kernel bugs being reported.
BTW, James and I are already discussing more coherent methods (see [0])
to manage this exporting of information to user-land (so to that we can
save ourselves from requiring to export new variables in the vmcoreinfo
in case we have similar changes to the virtual/physical address spaces
in future).
I will work on and send a patchset addressing the same shortly.
[0]. http://lists.infradead.org/pipermail/kexec/2019-June/023105.html
Thanks,
Bhupesh
_______________________________________________
kexec mailing list
kexec@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/kexec
