[lkml]   [2019]   [Jul]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v9 00/21] Generic page walk and ptdump
Hi Steven,

On Mon, Jul 29, 2019 at 12:32:25PM +0100, Steven Price wrote:
> parisc is more interesting and I'm not sure if this is necessarily
> correct. I originally proposed a patch with the line "For parisc, we
> don't support large pages, so add stubs returning 0" which got Acked by
> Helge Deller. However going back to look at that again I see there was a
> follow up thread[2] which possibly suggests I was wrong?

I just started a week ago implementing ptdump for PA-RISC. Didn't notice that
you're working on making it generic, which is nice. I'll adjust my code
to use the infrastructure you're currently developing.

> Can anyone shed some light on whether parisc does support leaf entries
> of the page table tree at a higher than the normal depth?
> [1]
> [2]

My understanding is that PA-RISC only has leaf entries on PTE level.

> The intention is that the page table walker would be available for all
> architectures so that it can be used in any generic code - PTDUMP simply
> seemed like a good place to start.
> > Now that pmd_leaf() and pud_leaf() are getting used in walk_page_range() these
> > functions need to be defined on all arch irrespective if they use PTDUMP or not
> > or otherwise just define it for archs which need them now for sure i.e x86 and
> > arm64 (which are moving to new generic PTDUMP framework). Other archs can
> > implement these later.

I'll take care of the PA-RISC part - for 32 bit your generic code works, for 64Bit
i need to learn a bit more about the following hack:

/* Allocate the top level pgd (page directory)
* Here (for 64 bit kernels) we implement a Hybrid L2/L3 scheme: we
* allocate the first pmd adjacent to the pgd. This means that we can
* subtract a constant offset to get to it. The pmd and pgd sizes are
* arranged so that a single pmd covers 4GB (giving a full 64-bit
* process access to 8TB) so our lookups are effectively L2 for the
* first 4GB of the kernel (i.e. for all ILP32 processes and all the
* kernel for machines with under 4GB of memory)

I see that your change clear P?D entries when p?d_bad() returns true, which - i think -
would be the case with the PA-RISC implementation.


 \ /
  Last update: 2019-07-31 11:28    [W:0.282 / U:0.152 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site