• Martin Schwidefsky's avatar
    s390/mm: add shadow gmap support · 4be130a0
    Martin Schwidefsky authored
    For a nested KVM guest the outer KVM host needs to create shadow
    page tables for the nested guest. This patch adds the basic support
    to the guest address space (gmap) code.
    
    For each guest address space the inner KVM host creates, the first
    outer KVM host needs to create shadow page tables. The address space
    is identified by the ASCE loaded into the control register 1 at the
    time the inner SIE instruction for the second nested KVM guest is
    executed. The outer KVM host creates the shadow tables starting with
    the table identified by the ASCE on a on-demand basis. The outer KVM
    host will get repeated faults for all the shadow tables needed to
    run the second KVM guest.
    
    While a shadow page table for the second KVM guest is active the access
    to the origin region, segment and page tables needs to be restricted
    for the first KVM guest. For region and segment and page tables the first
    KVM guest may read the memory, but write attempt has to lead to an
    unshadow.  This is done using the page invalid and read-only bits in the
    page table of the first KVM guest. If the first guest re-accesses one of
    the origin pages of a shadow, it gets a fault and the affected parts of
    the shadow page table hierarchy needs to be removed again.
    
    PGSTE tables don't have to be shadowed, as all interpretation assist can't
    deal with the invalid bits in the shadow pte being set differently than
    the original ones provided by the first KVM guest.
    
    Many bug fixes and improvements by David Hildenbrand.
    Reviewed-by: default avatarDavid Hildenbrand <dahi@linux.vnet.ibm.com>
    Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
    Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
    4be130a0
fault.c 19.9 KB