Re: [RFC PATCH rdma-next 01/10] RDMA: mr: Introduce is_pmem

[Dan Williams]

On Wed, Jan 5, 2022 at 10:13 PM lizhijian@xxxxxxxxxxx
<lizhijian@xxxxxxxxxxx> wrote:
>
>
> Add Dan to the party :)
>
> May i know whether there is any existing APIs to check whether
> a va/page backs to a nvdimm/pmem ?
>
>
>
> On 06/01/2022 08:21, Jason Gunthorpe wrote:
> > On Tue, Dec 28, 2021 at 04:07:08PM +0800, Li Zhijian wrote:
> >> We can use it to indicate whether the registering mr is associated with
> >> a pmem/nvdimm or not.
> >>
> >> Currently, we only assign it in rxe driver, for other device/drivers,
> >> they should implement it if needed.
> >>
> >> RDMA FLUSH will support the persistence feature for a pmem/nvdimm.
> >>
> >> Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxxxxx>
> >>   drivers/infiniband/sw/rxe/rxe_mr.c | 47 ++++++++++++++++++++++++++++++
> >>   include/rdma/ib_verbs.h            |  1 +
> >>   2 files changed, 48 insertions(+)
> >>
> >> diff --git a/drivers/infiniband/sw/rxe/rxe_mr.c b/drivers/infiniband/sw/rxe/rxe_mr.c
> >> index 7c4cd19a9db2..bcd5e7afa475 100644
> >> +++ b/drivers/infiniband/sw/rxe/rxe_mr.c
> >> @@ -162,6 +162,50 @@ void rxe_mr_init_dma(struct rxe_pd *pd, int access, struct rxe_mr *mr)
> >>      mr->type = IB_MR_TYPE_DMA;
> >>   }
> >>
> >> +// XXX: the logic is similar with mm/memory-failure.c
> >> +static bool page_in_dev_pagemap(struct page *page)
> >> +{
> >> +    unsigned long pfn;
> >> +    struct page *p;
> >> +    struct dev_pagemap *pgmap = NULL;
> >> +
> >> +    pfn = page_to_pfn(page);
> >> +    if (!pfn) {
> >> +            pr_err("no such pfn for page %p\n", page);
> >> +            return false;
> >> +    }
> >> +
> >> +    p = pfn_to_online_page(pfn);
> >> +    if (!p) {
> >> +            if (pfn_valid(pfn)) {
> >> +                    pgmap = get_dev_pagemap(pfn, NULL);
> >> +                    if (pgmap)
> >> +                            put_dev_pagemap(pgmap);
> >> +            }
> >> +    }
> >> +
> >> +    return !!pgmap;
> > You need to get Dan to check this out, but I'm pretty sure this should
> > be more like this:
> >
> > if (is_zone_device_page(page) && page->pgmap->type == MEMORY_DEVICE_FS_DAX)
>
> Great, i have added him.
>
>
>
> >
> >
> >> +static bool iova_in_pmem(struct rxe_mr *mr, u64 iova, int length)
> >> +{
> >> +    struct page *page = NULL;
> >> +    char *vaddr = iova_to_vaddr(mr, iova, length);
> >> +
> >> +    if (!vaddr) {
> >> +            pr_err("not a valid iova %llu\n", iova);
> >> +            return false;
> >> +    }
> >> +
> >> +    page = virt_to_page(vaddr);
> > And obviously this isn't uniform for the entire umem, so I don't even
> > know what this is supposed to mean.
>
> My intention is to check if a memory region belongs to a nvdimm/pmem.
> The approach is like that:
> iova(user space)-+                     +-> page -> page_in_dev_pagemap()
>                   |                     |
>                   +-> va(kernel space) -+
> Since current MR's va is associated with map_set where it record the relations
> between iova and va and page. Do do you mean we should travel map_set to
> get its page ? or by any other ways.

Apologies for the delay in responding.

The Subject line of this patch is confusing, if you want to know if a
pfn is in persistent memory the only mechanism for that is:

region_intersects(addr, length, IORESOURCE_MEM, IORES_DESC_PERSISTENT_MEMORY)

...there is otherwise nothing pmem specific about the dev_pagemap
infrastructure. Yes, pmem is the primary user, but it is also used for
mapping "soft-reserved" memory (See: the EFI_MEMORY_SP) attribute, and
other users.

Can you clarify the intent? I am missing some context.