• David Gibson's avatar
    [PATCH] ppc64: Fix bug in SLB miss handler for hugepages · 7d24f0b8
    David Gibson authored
    This patch, however, should be applied on top of the 64k-page-size patch to
    fix some problems with hugepage (some pre-existing, another introduced by
    this patch).
    
    The patch fixes a bug in the SLB miss handler for hugepages on ppc64
    introduced by the dynamic hugepage patch (commit id
    c594adad) due to a misunderstanding of the
    srd instruction's behaviour (mea culpa).  The problem arises when a 64-bit
    process maps some hugepages in the low 4GB of the address space (unusual).
    In this case, as well as the 256M segment in question being marked for
    hugepages, other segments at 32G intervals will be incorrectly marked for
    hugepages.
    
    In the process, this patch tweaks the semantics of the hugepage bitmaps to
    be more sensible.  Previously, an address below 4G was marked for hugepages
    if the appropriate segment bit in the "low areas" bitmask was set *or* if
    the low bit in the "high areas" bitmap was set (which would mark all
    addresses below 1TB for hugepage).  With this patch, any given address is
    governed by a single bitmap.  Addresses below 4GB are marked for hugepage
    if and only if their bit is set in the "low areas" bitmap (256M
    granularity).  Addresses between 4GB and 1TB are marked for hugepage iff
    the low bit in the "high areas" bitmap is set.  Higher addresses are marked
    for hugepage iff their bit in the "high areas" bitmap is set (1TB
    granularity).
    
    To avoid conflicts, this patch must be applied on top of BenH's pending
    patch for 64k base page size [0].  As such, this patch also addresses a
    hugepage problem introduced by that patch.  That patch allows hugepages of
    1MB in size on hardware which supports it, however, that won't work when
    using 4k pages (4 level pagetable), because in that case hugepage PTEs are
    stored at the PMD level, and each PMD entry maps 2MB.  This patch simply
    disallows hugepages in that case (we can do something cleverer to re-enable
    them some other day).
    
    Built, booted, and a handful of hugepage related tests passed on POWER5
    LPAR (both ARCH=powerpc and ARCH=ppc64).
    
    [0] http://gate.crashing.org/~benh/ppc64-64k-pages.diffSigned-off-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    7d24f0b8
slb_low.S 6.16 KB