lkml.org 
[lkml]   [2014]   [Oct]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v3 0/4] mm: new function to forbid zeropage mappings for a process


    On 10/22/2014 01:09 PM, Dominik Dingel wrote:
    > s390 has the special notion of storage keys which are some sort of page flags
    > associated with physical pages and live outside of direct addressable memory.
    > These storage keys can be queried and changed with a special set of instructions.
    > The mentioned instructions behave quite nicely under virtualization, if there is:
    > - an invalid pte, then the instructions will work on memory in the host page table
    > - a valid pte, then the instructions will work with the real storage key
    >
    > Thanks to Martin with his software reference and dirty bit tracking,
    > the kernel does not issue any storage key instructions as now a
    > software based approach will be taken, on the other hand distributions
    > in the wild are currently using them.
    >
    > However, for virtualized guests we still have a problem with guest pages
    > mapped to zero pages and the kernel same page merging.
    > With each one multiple guest pages will point to the same physical page
    > and share the same storage key.
    >
    > Let's fix this by introducing a new function which s390 will define to
    > forbid new zero page mappings. If the guest issues a storage key related
    > instruction we flag the mm_struct, drop existing zero page mappings
    > and unmerge the guest memory.
    >
    > v2 -> v3:
    > - Clearing up patch description Patch 3/4
    > - removing unnecessary flag in mmu_context (Paolo)

    ... and zero the mm_use_skey flag correctly, too. :)

    > v1 -> v2:
    > - Following Dave and Paolo suggestion removing the vma flag

    Thanks, the patches look good. I expect that they will either go in
    through the s390 tree, or come in via Christian.

    If the latter, Martin, please reply with your Acked-by.

    Paolo


    \
     
     \ /
      Last update: 2014-10-22 16:41    [W:3.138 / U:0.300 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site