On Thursday 11 February 2016 04:50 PM, Martin Schwidefsky wrote: > On Thu, 11 Feb 2016 16:23:33 +0530 > Vineet Gupta <Vineet.Gupta1 at synopsys.com> 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 at synopsys.com> 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. The current s390 code does something similar using a different struct cast. It is still writing in pgtable_t - although at a different location. > 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. Right so that is the problem - just trying to understand. > In short, please let s390 keep its own copy of deposit/withdraw. You got it - I'm out of the way :-) Thx, -Vineet
