Introduce a way for hmm_range_fault() and migrate_vma_setup() to identify
foreign devices with fast interconnect and thereby allow
both direct access over the interconnect and p2p migration.
The need for a callback arises because without it, the p2p ability would
need to be static and determined at dev_pagemap creation time. With
a callback it can be determined dynamically, and in the migrate case
the callback could separate out local device pages.
The hmm_range_fault() change has been tested internally, the
migrate_vma_setup() change hasn't yet.
Seeking early feedback. Any suggestions appreciated.
Cc: Matthew Brost <matthew.br...@intel.com>
Cc: Jason Gunthorpe <j...@nvidia.com>
Cc: Simona Vetter <simona.vet...@ffwll.ch>
Cc: DRI-devel <dri-devel@lists.freedesktop.org>
Cc: Linux Memory Management List <linux...@kvack.org>
Cc: LKML <linux-ker...@vger.kernel.org>
Signed-off-by: Thomas Hellström <thomas.hellst...@linux.intel.com>
---
include/linux/hmm.h | 2 ++
include/linux/migrate.h | 29 +++++++++++++++++++++++++++++
mm/hmm.c | 13 +++++++++++--
mm/migrate_device.c | 12 ++++++++++++
4 files changed, 54 insertions(+), 2 deletions(-)
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 126a36571667..4de909a1e10a 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -12,6 +12,7 @@
#include <linux/mm.h>
struct mmu_interval_notifier;
+struct p2p_allow;
/*
* On output:
@@ -97,6 +98,7 @@ struct hmm_range {
unsigned long default_flags;
unsigned long pfn_flags_mask;
void *dev_private_owner;
+ struct p2p_allow *p2p;
};
/*
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 002e49b2ebd9..0ff085b633e3 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -183,10 +183,37 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
return (pfn << MIGRATE_PFN_SHIFT) | MIGRATE_PFN_VALID;
}
+struct p2p_allow;
+
+/**
+ * struct p2p_allow_ops - Functions for detailed cross-device access.
+ */
+struct p2p_allow_ops {
+ /**
+ * @p2p_allow: Whether to allow cross-device access to device_private
pages.
+ * @allow: Pointer to a struct p2p_allow. Typically subclassed by the
caller
+ * to provide needed information.
+ * @page: The page being queried.
+ */
+ bool (*p2p_allow)(struct p2p_allow *allow, struct page *page);
+};
+
+/**
+ * struct p2p_allow - Information needed to allow cross-device access.
+ * @ops: Pointer to a struct p2p_allow_ops.
+ *
+ * This struct is intended to be embedded / subclassed to provide additional
+ * information needed by the @ops p2p_allow() callback.
+ */
+struct p2p_allow {
+ const struct p2p_allow_ops *ops;
+};
+
enum migrate_vma_direction {
MIGRATE_VMA_SELECT_SYSTEM = 1 << 0,
MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1,
MIGRATE_VMA_SELECT_DEVICE_COHERENT = 1 << 2,
+ MIGRATE_VMA_SELECT_DEVICE_P2P = 1 << 3,
};
struct migrate_vma {
@@ -222,6 +249,8 @@ struct migrate_vma {
* a migrate_to_ram() callback.
*/
struct page *fault_page;
+ /* Optional identification of devices for p2p migration */
+ struct p2p_allow *p2p;
};
int migrate_vma_setup(struct migrate_vma *args);
diff --git a/mm/hmm.c b/mm/hmm.c
index 7e0229ae4a5a..8c28f9b22ed2 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -19,6 +19,7 @@
#include <linux/pagemap.h>
#include <linux/swapops.h>
#include <linux/hugetlb.h>
+#include <linux/migrate.h>
#include <linux/memremap.h>
#include <linux/sched/mm.h>
#include <linux/jump_label.h>
@@ -220,6 +221,15 @@ static inline unsigned long pte_to_hmm_pfn_flags(struct
hmm_range *range,
return pte_write(pte) ? (HMM_PFN_VALID | HMM_PFN_WRITE) : HMM_PFN_VALID;
}
+static bool hmm_allow_devmem(struct hmm_range *range, struct page *page)
+{
+ if (likely(page->pgmap->owner == range->dev_private_owner))
+ return true;
+ if (likely(!range->p2p))
+ return false;
+ return range->p2p->ops->p2p_allow(range->p2p, page);
+}
+
static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
unsigned long end, pmd_t *pmdp, pte_t *ptep,
unsigned long *hmm_pfn)
@@ -248,8 +258,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk,
unsigned long addr,
* just report the PFN.
*/
if (is_device_private_entry(entry) &&
- pfn_swap_entry_to_page(entry)->pgmap->owner ==
- range->dev_private_owner) {
+ hmm_allow_devmem(range, pfn_swap_entry_to_page(entry))) {
cpu_flags = HMM_PFN_VALID;
if (is_writable_device_private_entry(entry))
cpu_flags |= HMM_PFN_WRITE;
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 9cf26592ac93..8e643a3872c9 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -54,6 +54,13 @@ static int migrate_vma_collect_hole(unsigned long start,
return 0;
}
+static bool migrate_vma_allow_p2p(struct migrate_vma *migrate, struct page
*page)
+{
+ if (likely(!migrate->p2p))
+ return false;
+ return migrate->p2p->ops->p2p_allow(migrate->p2p, page);
+}
+
static int migrate_vma_collect_pmd(pmd_t *pmdp,
unsigned long start,
unsigned long end,
@@ -138,6 +145,11 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
page->pgmap->owner != migrate->pgmap_owner)
goto next;
+ if (!(migrate->flags &
+ MIGRATE_VMA_SELECT_DEVICE_P2P) ||
+ !migrate_vma_allow_p2p(migrate, page))
+ goto next;
+
mpfn = migrate_pfn(page_to_pfn(page)) |
MIGRATE_PFN_MIGRATE;
if (is_writable_device_private_entry(entry))
--
2.46.0
