| Message ID | 20200402184819.34215-4-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: s390: vsie: fixes and cleanups. | expand |
On 02.04.20 20:48, David Hildenbrand wrote: > We have to properly retry again by returning -EINVAL immediately in case > somebody else instantiated the table concurrently. We missed to add the > goto in this function only. The code now matches the other, similar > shadowing functions. > > We are overwriting an existing region 2 table entry. All allocated pages > are added to the crst_list to be freed later, so they are not lost > forever. However, when unshadowing the region 2 table, we wouldn't trigger > unshadowing of the original shadowed region 3 table that we replaced. It > would get unshadowed when the original region 3 table is modified. As it's > not connected to the page table hierarchy anymore, it's not going to get > used anymore. However, for a limited time, this page table will stick > around, so it's in some sense a temporary memory leak. > > Identified by manual code inspection. I don't think this classifies as > stable material. > > Fixes: 998f637cc4b9 ("s390/mm: avoid races on region/segment/page table shadowing") > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > arch/s390/mm/gmap.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c > index f3dbc5bdde50..fd32ab566f57 100644 > --- a/arch/s390/mm/gmap.c > +++ b/arch/s390/mm/gmap.c > @@ -1844,6 +1844,7 @@ int gmap_shadow_r3t(struct gmap *sg, unsigned long saddr, unsigned long r3t, > goto out_free; > } else if (*table & _REGION_ENTRY_ORIGIN) { > rc = -EAGAIN; /* Race with shadow */ > + goto out_free; > } > crst_table_init(s_r3t, _REGION3_ENTRY_EMPTY); > /* mark as invalid as long as the parent table is not protected */ Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c index f3dbc5bdde50..fd32ab566f57 100644 --- a/arch/s390/mm/gmap.c +++ b/arch/s390/mm/gmap.c @@ -1844,6 +1844,7 @@ int gmap_shadow_r3t(struct gmap *sg, unsigned long saddr, unsigned long r3t, goto out_free; } else if (*table & _REGION_ENTRY_ORIGIN) { rc = -EAGAIN; /* Race with shadow */ + goto out_free; } crst_table_init(s_r3t, _REGION3_ENTRY_EMPTY); /* mark as invalid as long as the parent table is not protected */
We have to properly retry again by returning -EINVAL immediately in case somebody else instantiated the table concurrently. We missed to add the goto in this function only. The code now matches the other, similar shadowing functions. We are overwriting an existing region 2 table entry. All allocated pages are added to the crst_list to be freed later, so they are not lost forever. However, when unshadowing the region 2 table, we wouldn't trigger unshadowing of the original shadowed region 3 table that we replaced. It would get unshadowed when the original region 3 table is modified. As it's not connected to the page table hierarchy anymore, it's not going to get used anymore. However, for a limited time, this page table will stick around, so it's in some sense a temporary memory leak. Identified by manual code inspection. I don't think this classifies as stable material. Fixes: 998f637cc4b9 ("s390/mm: avoid races on region/segment/page table shadowing") Signed-off-by: David Hildenbrand <david@redhat.com> --- arch/s390/mm/gmap.c | 1 + 1 file changed, 1 insertion(+)