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] https://lkml.org/lkml/2019/2/27/572 > [2] https://lkml.org/lkml/2019/3/5/610 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: arch/parisc/include/asm/pgalloc.h:15 /* 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. Regards Sven
