• Martin Schwidefsky's avatar
    [S390] fix tlb flushing for page table pages · cd94154c
    Martin Schwidefsky authored
    Git commit 36409f63 "use generic RCU
    page-table freeing code" introduced a tlb flushing bug. Partially revert
    the above git commit and go back to s390 specific page table flush code.
    For s390 the TLB can contain three types of entries, "normal" TLB
    page-table entries, TLB combined region-and-segment-table (CRST) entries
    and real-space entries. Linux does not use real-space entries which
    leaves normal TLB entries and CRST entries. The CRST entries are
    intermediate steps in the page-table translation called translation paths.
    For example a 4K page access in a three-level page table setup will
    create two CRST TLB entries and one page-table TLB entry. The advantage
    of that approach is that a page access next to the previous one can reuse
    the CRST entries and needs just a single read from memory to create the
    page-table TLB entry. The disadvantage is that the TLB flushing rules are
    more complicated, before any page-table may be freed the TLB needs to be
    In short: the generic RCU page-table freeing code is incorrect for the
    CRST entries, in particular the check for mm_users < 2 is troublesome.
    This is applicable to 3.0+ kernels.
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
pgtable.c 22.6 KB