On 22.01.2018 13:09, Janosch Frank wrote: > On 22.01.2018 12:56, David Hildenbrand wrote: >> On 13.12.2017 13:53, Janosch Frank wrote: >>> For later migration of huge pages we want to write-protect guest >>> PMDs. While doing this, we have to make absolutely sure, that the >>> guest's lowcore is always accessible when the VCPU is running. With >>> PTEs, this is solved by marking the PGSTEs of the lowcore pages with >>> the invalidation notification bit and kicking the guest out of the SIE >>> via a notifier function if we need to invalidate such a page. >>> >>> With PMDs we do not have PGSTEs or some other bits we could use in the >>> host PMD. Instead we pick one of the free bits in the gmap PMD. Every >>> time a host pmd will be invalidated, we will check if the respective >>> gmap PMD has the bit set and in that case fire up the notifier. >>> >>> In the first step we only support setting the invalidation bit, but we >>> do not support restricting access of guest pmds. It will follow >>> shortly. >>> >>> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxxxxxxx> >>> --- >>> arch/s390/include/asm/gmap.h | 3 ++ >>> arch/s390/include/asm/pgtable.h | 7 +++- >>> arch/s390/mm/gmap.c | 92 ++++++++++++++++++++++++++++++++++++----- >>> arch/s390/mm/pgtable.c | 4 ++ >>> 4 files changed, 94 insertions(+), 12 deletions(-) >>> >>> diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h >>> index c1bc563..21bb658 100644 >>> --- a/arch/s390/include/asm/gmap.h >>> +++ b/arch/s390/include/asm/gmap.h >>> @@ -13,6 +13,9 @@ >>> #define GMAP_NOTIFY_SHADOW 0x2 >>> #define GMAP_NOTIFY_MPROT 0x1 >>> >>> +/* Status bits in the gmap segment entry. */ >>> +#define _SEGMENT_ENTRY_GMAP_IN 0x0001 /* invalidation notify bit */ >>> + >> >> _SEGMENT_ENTRY_READ -> 0x0001 >> >> Is it even okay to reuse that bit? >> > > It's in the GMAP segment entry, not in the process' segment entry. > That's why we throw away all software bits from the process entry when > linking into the gmap table. > Ah right, we only share page tables but not complete segments. Thanks. -- Thanks, David / dhildenb
