On Wed, 6 May 2015 14:29:39 +0300 "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> wrote: > I'm looking though s390 code around page table handling and I found that > in many places s390 does tlb flush before changing page table entry. Uhh, have fun with that.. it is complicated :-/ > Let's look for instance on pmdp_clear_flush() implementation on s390. > It's implemented with pmdp_get_and_clear() which does pmdp_flush_direct() > *before* pmd_clear(). That's invert order comparing to generic > pmdp_flush_direct(). > > The question is what prevents tlb from being re-fill between flushing tlb > and clearing page table entry? Look again at pmdp_flush_direct(), either __pmdp_idte_local or __pmdp_idte is called. Both functions use the IDTE instruction but in two different flavors. The mnemonic IDTE stands for invalidate-dat-table-entry, the instruction sets the invalid bit in the PMD and flushes all TLB entries on all CPUs that are affected by the now invalid PMD. The pmd_clear after the pmdp_flush_direct is done to set all the other bits of the PMD to the "empty" state. The invalid bit is already set prior to pmd_clear. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>