On 03.04.20 17:30, David Hildenbrand wrote:
In case we have a region 1 ASCE, our shadow/g3 address can have any value. Unfortunately, (-1UL << 64) is undefined and triggers sometimes, rejecting valid shadow addresses when trying to walk our shadow table hierarchy.
I thin the range of the addresses do not matter. Took me a while to understand maybe rephrase that:
In case we have a region 1 the following calculation (31 + ((gmap->asce & _ASCE_TYPE_MASK) >> 2)*11) results in 64. As shifts beyond the size are undefined the compiler is free to use instructions like sllg. sllg will only use 6 bits of the shift value (here 64) resulting in no shift at all. That means that ALL addresses will be rejected.
With that this makes sense.
Reviewed-by: Christian Borntraeger borntraeger@de.ibm.com
The result is that the prefix cannot get mapped and will loop basically forever trying to map it (-EAGAIN loop).
After all, the broken check is only a sanity check, our table shadowing code in kvm_s390_shadow_tables() already checks these conditions, injecting proper translation exceptions. Turn it into a WARN_ON_ONCE().
Fixes: 4be130a08420 ("s390/mm: add shadow gmap support") Tested-by: Janosch Frank frankja@linux.ibm.com Reported-by: Janosch Frank frankja@linux.ibm.com Cc: stable@vger.kernel.org # v4.8+ Signed-off-by: David Hildenbrand david@redhat.com
arch/s390/mm/gmap.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c index 2fbece47ef6f..b93dd54b234a 100644 --- a/arch/s390/mm/gmap.c +++ b/arch/s390/mm/gmap.c @@ -787,14 +787,18 @@ static void gmap_call_notifier(struct gmap *gmap, unsigned long start, static inline unsigned long *gmap_table_walk(struct gmap *gmap, unsigned long gaddr, int level) {
- const int asce_type = gmap->asce & _ASCE_TYPE_MASK; unsigned long *table;
if ((gmap->asce & _ASCE_TYPE_MASK) + 4 < (level * 4)) return NULL; if (gmap_is_shadow(gmap) && gmap->removed) return NULL;
- if (gaddr & (-1UL << (31 + ((gmap->asce & _ASCE_TYPE_MASK) >> 2)*11)))
- if (WARN_ON_ONCE(asce_type != _ASCE_TYPE_REGION1 &&
gaddr & (-1UL << (31 + (asce_type >> 2) * 11))))- table = gmap->table; switch (gmap->asce & _ASCE_TYPE_MASK) { case _ASCE_TYPE_REGION1: