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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, "Dan Williams" <dan.j.williams@intel.com>,
	"Logan Gunthorpe" <logang@deltatee.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Michal Hocko" <mhocko@suse.com>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Balbir Singh" <bsingharora@gmail.com>
Subject: [PATCH 4.20 15/65] mm, hmm: mark hmm_devmem_{add, add_resource} EXPORT_SYMBOL_GPL
Date: Fri, 11 Jan 2019 15:15:01 +0100
Message-ID: <20190111131058.494129031@linuxfoundation.org> (raw)
In-Reply-To: <20190111131055.331350141@linuxfoundation.org>

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@intel.com>

commit 02917e9f8676207a4c577d4d94eae12bf348e9d7 upstream.

At Maintainer Summit, Greg brought up a topic I proposed around
EXPORT_SYMBOL_GPL usage.  The motivation was considerations for when
EXPORT_SYMBOL_GPL is warranted and the criteria for taking the exceptional
step of reclassifying an existing export.  Specifically, I wanted to make
the case that although the line is fuzzy and hard to specify in abstract
terms, it is nonetheless clear that devm_memremap_pages() and HMM
(Heterogeneous Memory Management) have crossed it.  The
devm_memremap_pages() facility should have been EXPORT_SYMBOL_GPL from the
beginning, and HMM as a derivative of that functionality should have
naturally picked up that designation as well.

Contrary to typical rules, the HMM infrastructure was merged upstream with
zero in-tree consumers.  There was a promise at the time that those users
would be merged "soon", but it has been over a year with no drivers
arriving.  While the Nouveau driver is about to belatedly make good on
that promise it is clear that HMM was targeted first and foremost at an
out-of-tree consumer.

HMM is derived from devm_memremap_pages(), a facility Christoph and I
spearheaded to support persistent memory.  It combines a device lifetime
model with a dynamically created 'struct page' / memmap array for any
physical address range.  It enables coordination and control of the many
code paths in the kernel built to interact with memory via 'struct page'
objects.  With HMM the integration goes even deeper by allowing device
drivers to hook and manipulate page fault and page free events.

One interpretation of when EXPORT_SYMBOL is suitable is when it is
exporting stable and generic leaf functionality.  The
devm_memremap_pages() facility continues to see expanding use cases,
peer-to-peer DMA being the most recent, with no clear end date when it
will stop attracting reworks and semantic changes.  It is not suitable to
export devm_memremap_pages() as a stable 3rd party driver API due to the
fact that it is still changing and manipulates core behavior.  Moreover,
it is not in the best interest of the long term development of the core
memory management subsystem to permit any external driver to effectively
define its own system-wide memory management policies with no
encouragement to engage with upstream.

I am also concerned that HMM was designed in a way to minimize further
engagement with the core-MM.  That, with these hooks in place,
device-drivers are free to implement their own policies without much
consideration for whether and how the core-MM could grow to meet that
need.  Going forward not only should HMM be EXPORT_SYMBOL_GPL, but the
core-MM should be allowed the opportunity and stimulus to change and
address these new use cases as first class functionality.

Original changelog:

hmm_devmem_add(), and hmm_devmem_add_resource() duplicated
devm_memremap_pages() and are now simple now wrappers around the core
facility to inject a dev_pagemap instance into the global pgmap_radix and
hook page-idle events.  The devm_memremap_pages() interface is base
infrastructure for HMM.  HMM has more and deeper ties into the kernel
memory management implementation than base ZONE_DEVICE which is itself a
EXPORT_SYMBOL_GPL facility.

Originally, the HMM page structure creation routines copied the
devm_memremap_pages() code and reused ZONE_DEVICE.  A cleanup to unify the
implementations was discussed during the initial review:
http://lkml.iu.edu/hypermail/linux/kernel/1701.2/00812.html Recent work to
extend devm_memremap_pages() for the peer-to-peer-DMA facility enabled
this cleanup to move forward.

In addition to the integration with devm_memremap_pages() HMM depends on
other GPL-only symbols:

    mmu_notifier_unregister_no_release
    percpu_ref
    region_intersects
    __class_create

It goes further to consume / indirectly expose functionality that is not
exported to any other driver:

    alloc_pages_vma
    walk_page_range

HMM is derived from devm_memremap_pages(), and extends deep core-kernel
fundamentals. Similar to devm_memremap_pages(), mark its entry points
EXPORT_SYMBOL_GPL().

[logang@deltatee.com: PCI/P2PDMA: match interface changes to devm_memremap_pages()]
  Link: http://lkml.kernel.org/r/20181130225911.2900-1-logang@deltatee.com
Link: http://lkml.kernel.org/r/154275560565.76910.15919297436557795278.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Balbir Singh <bsingharora@gmail.com>,
Cc: Michal Hocko <mhocko@suse.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/pci/p2pdma.c |   10 ++--------
 mm/hmm.c             |    4 ++--
 2 files changed, 4 insertions(+), 10 deletions(-)

--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -82,10 +82,8 @@ static void pci_p2pdma_percpu_release(st
 	complete_all(&p2p->devmap_ref_done);
 }
 
-static void pci_p2pdma_percpu_kill(void *data)
+static void pci_p2pdma_percpu_kill(struct percpu_ref *ref)
 {
-	struct percpu_ref *ref = data;
-
 	/*
 	 * pci_p2pdma_add_resource() may be called multiple times
 	 * by a driver and may register the percpu_kill devm action multiple
@@ -198,6 +196,7 @@ int pci_p2pdma_add_resource(struct pci_d
 	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
 	pgmap->pci_p2pdma_bus_offset = pci_bus_address(pdev, bar) -
 		pci_resource_start(pdev, bar);
+	pgmap->kill = pci_p2pdma_percpu_kill;
 
 	addr = devm_memremap_pages(&pdev->dev, pgmap);
 	if (IS_ERR(addr)) {
@@ -211,11 +210,6 @@ int pci_p2pdma_add_resource(struct pci_d
 	if (error)
 		goto pgmap_free;
 
-	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_percpu_kill,
-					  &pdev->p2pdma->devmap_ref);
-	if (error)
-		goto pgmap_free;
-
 	pci_info(pdev, "added peer-to-peer DMA memory %pR\n",
 		 &pgmap->res);
 
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -1110,7 +1110,7 @@ struct hmm_devmem *hmm_devmem_add(const
 		return result;
 	return devmem;
 }
-EXPORT_SYMBOL(hmm_devmem_add);
+EXPORT_SYMBOL_GPL(hmm_devmem_add);
 
 struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
 					   struct device *device,
@@ -1164,7 +1164,7 @@ struct hmm_devmem *hmm_devmem_add_resour
 		return result;
 	return devmem;
 }
-EXPORT_SYMBOL(hmm_devmem_add_resource);
+EXPORT_SYMBOL_GPL(hmm_devmem_add_resource);
 
 /*
  * A device driver that wants to handle multiple devices memory through a



  parent reply index

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-11 14:14 [PATCH 4.20 00/65] 4.20.2-stable review Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 01/65] scsi: zfcp: fix posting too many status read buffers leading to adapter shutdown Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 02/65] scsi: lpfc: do not set queue->page_count to 0 if pc_sli4_params.wqpcnt is invalid Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 03/65] fork: record start_time late Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 04/65] zram: fix double free backing device Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 05/65] hwpoison, memory_hotplug: allow hwpoisoned pages to be offlined Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 06/65] mm, devm_memremap_pages: mark devm_memremap_pages() EXPORT_SYMBOL_GPL Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 07/65] mm, devm_memremap_pages: kill mapping "System RAM" support Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 08/65] mm, devm_memremap_pages: fix shutdown handling Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 09/65] memcg, oom: notify on oom killer invocation from the charge path Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 10/65] sunrpc: fix cache_head leak due to queued request Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 11/65] sunrpc: use SVC_NET() in svcauth_gss_* functions Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 12/65] mm, devm_memremap_pages: add MEMORY_DEVICE_PRIVATE support Greg Kroah-Hartman
2019-01-11 14:14 ` [PATCH 4.20 13/65] mm, hmm: use devm semantics for hmm_devmem_{add, remove} Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 14/65] mm, hmm: replace hmm_devmem_pages_create() with devm_memremap_pages() Greg Kroah-Hartman
2019-01-11 14:15 ` Greg Kroah-Hartman [this message]
2019-01-11 14:15 ` [PATCH 4.20 16/65] mm, swap: fix swapoff with KSM pages Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 17/65] media: cx23885: only reset DMA on problematic CPUs Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 18/65] ALSA: cs46xx: Potential NULL dereference in probe Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 19/65] ALSA: usb-audio: Avoid access before bLength check in build_audio_procunit() Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 20/65] ALSA: usb-audio: Check mixer unit descriptors more strictly Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 21/65] ALSA: usb-audio: Fix an out-of-bound read in create_composite_quirks Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 22/65] ALSA: usb-audio: Always check descriptor sizes in parser code Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 23/65] srcu: Lock srcu_data structure in srcu_gp_start() Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 24/65] driver core: Add missing dev->bus->need_parent_lock checks Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 25/65] Fix failure path in alloc_pid() Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 26/65] block: deactivate blk_stat timer in wbt_disable_default() Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 27/65] block: mq-deadline: Fix write completion handling Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 28/65] dm: do not allow readahead to limit IO size Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 29/65] dlm: fixed memory leaks after failed ls_remove_names allocation Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 30/65] dlm: possible memory leak on error path in create_lkb() Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 31/65] dlm: lost put_lkb on error path in receive_convert() and receive_unlock() Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 32/65] dlm: memory leaks on error path in dlm_user_request() Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 33/65] gfs2: Get rid of potential double-freeing in gfs2_create_inode Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 34/65] gfs2: Fix loop in gfs2_rbm_find Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 35/65] b43: Fix error in cordic routine Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 36/65] selinux: policydb - fix byte order and alignment issues Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 37/65] PCI / PM: Allow runtime PM without callback functions Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 38/65] lockd: Show pid of lockd for remote locks Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 39/65] xprtrdma: Yet another double DMA-unmap Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 40/65] nfsd4: zero-length WRITE should succeed Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 41/65] Revert "powerpc/tm: Unset MSR[TS] if not recheckpointing" Greg Kroah-Hartman
2019-01-12 21:35   ` Christoph Biedl
2019-01-13  7:11     ` Greg Kroah-Hartman
2019-01-14  0:00       ` Michael Ellerman
2019-01-14  8:10         ` Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 42/65] powerpc/tm: Set MSR[TS] just prior to recheckpoint Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 43/65] iio: adc: qcom-spmi-adc5: Initialize prescale properly Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 44/65] iio: dac: ad5686: fix bit shift read register Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 45/65] 9p/net: put a lower bound on msize Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 46/65] rxe: fix error completion wr_id and qp_num Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 47/65] stm class: Fix a module refcount leak in policy creation error path Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 48/65] RDMA/srpt: Fix a use-after-free in the channel release code Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 49/65] RDMA/iwcm: Dont copy past the end of dev_name() string Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 50/65] iommu/vt-d: Handle domain agaw being less than iommu agaw Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 51/65] sched/fair: Fix infinite loop in update_blocked_averages() by reverting a9e7f6544b9c Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 52/65] ceph: dont update importing caps mseq when handing cap export Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 53/65] video: fbdev: pxafb: Fix "WARNING: invalid free of devm_ allocated data" Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 54/65] drivers/perf: hisi: Fixup one DDRC PMU register offset Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 55/65] powerpc/4xx/ocm: Fix compilation error due to PAGE_KERNEL usage Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 56/65] selftests: Fix test errors related to lib.mk khdr target Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 57/65] genwqe: Fix size check Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 58/65] intel_th: msu: Fix an off-by-one in attribute store Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 59/65] power: supply: olpc_battery: correct the temperature units Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 60/65] of: of_node_get()/of_node_put() nodes held in phandle cache Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 61/65] of: __of_detach_node() - remove node from " Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 62/65] lib: fix build failure in CONFIG_DEBUG_VIRTUAL test Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 63/65] drm/nouveau/drm/nouveau: Check rc from drm_dp_mst_topology_mgr_resume() Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 64/65] drm/vc4: Set ->is_yuv to false when num_planes == 1 Greg Kroah-Hartman
2019-01-11 14:15 ` [PATCH 4.20 65/65] drm/rockchip: psr: do not dereference encoder before it is null checked Greg Kroah-Hartman
2019-01-11 21:35 ` [PATCH 4.20 00/65] 4.20.2-stable review shuah
2019-01-12  8:03   ` Greg Kroah-Hartman
2019-01-12  8:28 ` Naresh Kamboju
2019-01-12 17:35   ` Greg Kroah-Hartman
2019-01-12 17:45 ` Guenter Roeck

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