From: Logan Gunthorpe <logang@deltatee.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: akpm@linux-foundation.org, Dave Hansen <dave@sr71.net>,
linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org,
Matthew Wilcox <willy@linux.intel.com>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Stephen Bates <Stephen.Bates@pmcs.com>
Subject: Re: [PATCH 14/15] mm, dax, pmem: introduce {get|put}_dev_pagemap() for dax-gup
Date: Fri, 2 Oct 2015 15:21:37 -0600 [thread overview]
Message-ID: <20151002212137.GB30448@deltatee.com> (raw)
In-Reply-To: <20150923044227.36490.99741.stgit@dwillia2-desk3.jf.intel.com>
Hi Dan,
We've been doing some experimenting and testing with this patchset.
Specifically, we are trying to use you're ZONE_DEVICE work to enable
peer to peer PCIe transfers. This is actually working pretty well
(though we're still testing and working through some things).
However, we've found a couple of issues:
On Wed, Sep 23, 2015 at 12:42:27AM -0400, Dan Williams wrote:
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 3d6baa7d4534..20097e7b679a 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -49,12 +49,16 @@ struct page {
> * updated asynchronously */
> union {
> struct address_space *mapping; /* If low bit clear, points to
> - * inode address_space, or NULL.
> + * inode address_space, unless
> + * the page is in ZONE_DEVICE
> + * then it points to its parent
> + * dev_pagemap, otherwise NULL.
> * If page mapped as anonymous
> * memory, low bit is set, and
> * it points to anon_vma object:
> * see PAGE_MAPPING_ANON below.
> */
> + struct dev_pagemap *pgmap;
> void *s_mem; /* slab first object */
> };
When you add to this union and overide the mapping value, we see bugs
in calls to set_page_dirty when it tries to dereference mapping. I believe
a change to page_mapping is required such as the patch that's at the end of
this email.
> diff --git a/mm/gup.c b/mm/gup.c
> index a798293fc648..1064e9a489a4 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -98,7 +98,16 @@ retry:
> }
>
> page = vm_normal_page(vma, address, pte);
> - if (unlikely(!page)) {
> + if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
> + /*
> + * Only return device mapping pages in the FOLL_GET case since
> + * they are only valid while holding the pgmap reference.
> + */
> + if (get_dev_pagemap(pte_pfn(pte), NULL))
> + page = pte_page(pte);
> + else
> + goto no_page;
> + } else if (unlikely(!page)) {
I've found that if a driver creates a ZONE_DEVICE mapping but doesn't
create the pagemap (using devm_register_pagemap) then the get_user_pages code
will go into an infinite loop. I'm not really sure if this as an issue or
not but it seems a bit undesirable for a buggy driver to be able to cause this.
My thoughts are that either devm_register_pagemap needs to be done by
devm_memremap_pages so a driver cannot use one without the other,
or the GUP code needs to return EFAULT if no pagemap was registered so
it doesn't loop forever.
Thanks!
Logan
diff --git a/mm/util.c b/mm/util.c
index 68ff8a5..19af683 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -368,6 +368,9 @@ struct address_space *page_mapping(struct page *page)
return swap_address_space(entry);
}
+ if (unlikely(is_zone_device_page(page)))
+ return NULL;
+
mapping = (unsigned long)page->mapping;
if (mapping & PAGE_MAPPING_FLAGS)
return NULL;
--
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next prev parent reply other threads:[~2015-10-02 21:21 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-23 4:41 [PATCH 00/15] get_user_pages() for dax mappings Dan Williams
2015-09-23 4:41 ` [PATCH 01/15] avr32: convert to asm-generic/memory_model.h Dan Williams
2015-09-24 15:10 ` Christoph Hellwig
2015-09-26 0:36 ` Dan Williams
2015-09-26 20:10 ` Christoph Hellwig
2015-09-28 18:44 ` Luck, Tony
2015-09-23 4:41 ` [PATCH 02/15] hugetlb: fix compile error on tile Dan Williams
2015-09-23 4:41 ` [PATCH 03/15] frv: fix compiler warning from definition of __pmd() Dan Williams
2015-09-23 4:41 ` [PATCH 04/15] x86, mm: quiet arch_add_memory() Dan Williams
2015-09-24 15:10 ` Christoph Hellwig
2015-09-23 4:41 ` [PATCH 05/15] pmem: kill memremap_pmem() Dan Williams
2015-09-24 15:11 ` Christoph Hellwig
2015-09-23 4:41 ` [PATCH 06/15] devm_memunmap: use devres_release() Dan Williams
2015-09-24 15:13 ` Christoph Hellwig
2015-09-23 4:41 ` [PATCH 07/15] devm_memremap: convert to return ERR_PTR Dan Williams
2015-09-24 15:13 ` Christoph Hellwig
2015-09-23 4:41 ` [PATCH 08/15] block, dax, pmem: reference counting infrastructure Dan Williams
2015-09-24 15:15 ` Christoph Hellwig
2015-09-25 0:03 ` Dan Williams
2015-09-25 11:32 ` Christoph Hellwig
2015-09-25 21:08 ` Williams, Dan J
2015-09-23 4:42 ` [PATCH 09/15] block, pmem: fix null pointer de-reference on shutdown, check for queue death Dan Williams
2015-09-23 4:42 ` [PATCH 10/15] block, dax: fix lifetime of in-kernel dax mappings Dan Williams
2015-10-07 22:56 ` Logan Gunthorpe
2015-10-09 21:12 ` Dan Williams
2015-09-23 4:42 ` [PATCH 11/15] mm, dax, pmem: introduce __pfn_t Dan Williams
2015-09-23 16:02 ` Dave Hansen
2015-09-23 23:36 ` Williams, Dan J
2015-09-23 4:42 ` [PATCH 12/15] mm, dax, gpu: convert vm_insert_mixed to __pfn_t, introduce _PAGE_DEVMAP Dan Williams
2015-09-23 13:47 ` Geert Uytterhoeven
2015-09-23 16:59 ` Dan Williams
2015-09-23 4:42 ` [PATCH 13/15] mm, dax: convert vmf_insert_pfn_pmd() to __pfn_t Dan Williams
2015-09-23 4:42 ` [PATCH 14/15] mm, dax, pmem: introduce {get|put}_dev_pagemap() for dax-gup Dan Williams
2015-10-02 21:21 ` Logan Gunthorpe [this message]
2015-10-02 21:53 ` Dan Williams
2015-10-02 22:14 ` Logan Gunthorpe
2015-10-02 22:42 ` Logan Gunthorpe
2015-10-02 22:55 ` Dan Williams
2015-09-23 4:42 ` [PATCH 15/15] mm, x86: get_user_pages() for dax mappings Dan Williams
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