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.
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