Re: [PATCH RFC 2/3] mm: Add support for exposing if dev_pagemap supports refcount pinning

Add a means of exposing if a pagemap supports refcount pinning. I am doing this to expose if a given pagemap has backing struct pages that will allow for the reference count of the page to be incremented to lock the page into place. The KVM code already has several spots where it was trying to use a pfn_valid check combined with a PageReserved check to determien if it could take a reference on the page. I am adding this check so in the case of the page having the reserved flag checked we can check the pagemap for the page to determine if we might fall into the special DAX case. Signed-off-by: Alexander Duyck <alexander.h.duyck(a)linux.intel.com&gt; --- drivers/nvdimm/pfn_devs.c | 2 ++ include/linux/memremap.h | 5 ++++- include/linux/mm.h | 11 +++++++++++ 3 files changed, 17 insertions(+), 1 deletion(-) diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c index 6f22272e8d80..7a4a85bcf7f4 100644 --- a/drivers/nvdimm/pfn_devs.c +++ b/drivers/nvdimm/pfn_devs.c @@ -640,6 +640,8 @@ static int __nvdimm_setup_pfn(struct nd_pfn *nd_pfn, struct dev_pagemap *pgmap) } else return -ENXIO; + pgmap->support_refcount_pinning = true; +