Messages in this thread | | | Subject | Re: [PATCH v3 3/3] mm/hmm/test: add self tests for HMM | From | Ralph Campbell <> | Date | Thu, 31 Oct 2019 10:48:18 -0700 |
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On 10/31/19 10:34 AM, Jason Gunthorpe wrote: > On Thu, Oct 31, 2019 at 10:28:12AM -0700, Ralph Campbell wrote: >>>>>>> It seems especially over-complicated to use a full page table layout >>>>>>> for this, wouldn't something simple like an xarray be good enough for >>>>>>> test purposes? >>>>>> >>>>>> Possibly. A page table is really just a lookup table from virtual address >>>>>> to pfn/page. Part of the rationale was to mimic what a real device >>>>>> might do. >>>>> >>>>> Well, but the details of the page table layout don't see really >>>>> important to this testing, IMHO. >>>> >>>> One problem with XArray is that on 32-bit machines the value would >>>> need to be u64 to hold a pfn which won't fit in a ULONG_MAX. >>>> I guess we could make the driver 64-bit only. >>> >>> Why would a 32 bit machine need a 64 bit pfn? >>> >> >> On x86, Physical Address Extension (PAE) uses a 64 bit PTE. >> See arch/x86/include/asm/pgtable_32_types.h which includes >> arch/x86/include/asm/pgtable-3level_types.h. > > That is the content of the PTE, not the address of the PTE. In this > case the xarray index is the 'virtual' address of the fictional device > and it can easily be 32 bits with no problem > > Jason >
Oh, I see. You mean use a 32-bit user virtual address for the index and store a pointer to the 64-bit PTE which of course would be 32 bit. That should work. I was stuck on thinking the PTE needed to be stored.
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