On Thu, 11 Feb 2016 16:23:33 +0530 Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx> wrote: > On Thursday 11 February 2016 03:52 PM, Martin Schwidefsky wrote: > > On Thu, 11 Feb 2016 14:58:26 +0530 > > Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx> wrote: > > > >> Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw() > >> assume pgtable_t to be struct page * which is not true for all arches. > >> Thus arc, s390, sparch end up with their own copies despite no special > >> hardware requirements (unlike powerpc). > > > > s390 does have a special hardware requirement. pgtable_t is an address > > for a 2K block of memory. It is *not* equivalent to a struct page * > > which refers to a 4K block of memory. That has been the whole point > > to introduce pgtable_t. > > Actually my reference to hardware requirement was more like powerpc style save a > hash value some where etc. > > Now pgtable_t need not be struct page * even if the actual sizes are same - e.g. > in ARC port I kept pgtable_t as pte_t * simply to avoid a few page_address() calls > in mm code (you could argue that is was a micro-optimization, anyways..) > > So given I know nothing about s390 MMU internals, I still think you can switch to > the update generic version despite 2K vs. 4K. Agree ? No, we can not. For s390 a page table is aligned on a 2K boundary and is only half the size of a page (except for KVM but that is another story). For s390 a pgtable_t is a pointer to the memory location with the 256 ptes and not a struct page *. The cast "struct page *new = (struct page*)pgtable;" in your first patch is already broken, "new" points to the memory of the page table and the list_head operations will clobber that memory. You try to fix it up with the memset to zero in pgtable_trans_huge_withdraw but that does not correct the pte entries for s390 as an invalid page-table entry is *not* all zeros. In short, please let s390 keep its own copy of deposit/withdraw. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
