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Subject[PATCH 22/36] HMM: add new callback for copying memory from and to device memory.
Date
From: Jerome Glisse <jglisse@redhat.com>

This patch only adds the new callback device driver must implement
to copy memory from and to device memory.

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Sherry Cheung <SCheung@nvidia.com>
Signed-off-by: Subhash Gutti <sgutti@nvidia.com>
Signed-off-by: Mark Hairgrove <mhairgrove@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Jatin Kumar <jakumar@nvidia.com>
---
include/linux/hmm.h | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++++
mm/hmm.c | 2 +
2 files changed, 105 insertions(+)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index f243eb5..eb30418 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -66,6 +66,8 @@ enum hmm_etype {
HMM_DEVICE_RFAULT,
HMM_DEVICE_WFAULT,
HMM_WRITE_PROTECT,
+ HMM_COPY_FROM_DEVICE,
+ HMM_COPY_TO_DEVICE,
};

/* struct hmm_event - memory event information.
@@ -157,6 +159,107 @@ struct hmm_device_ops {
* All other return value trigger warning and are transformed to -EIO.
*/
int (*update)(struct hmm_mirror *mirror,const struct hmm_event *event);
+
+ /* copy_from_device() - copy from device memory to system memory.
+ *
+ * @mirror: The mirror that link process address space with the device.
+ * @event: The event that triggered the copy.
+ * @dst: Array containing hmm_pte of destination memory.
+ * @start: Start address of the range (sub-range of event) to copy.
+ * @end: End address of the range (sub-range of event) to copy.
+ * Returns: 0 on success, error code otherwise {-ENOMEM, -EIO}.
+ *
+ * Called when migrating memory from device memory to system memory.
+ * The dst array contains valid DMA address for the device of the page
+ * to copy to (or pfn of page if hmm_device.device == NULL).
+ *
+ * If event.etype == HMM_FORK then device driver only need to schedule
+ * a copy to the system pages given in the dst hmm_pte array. Do not
+ * update the device page, and do not pause/stop the device threads
+ * that are using this address space. Just copy memory.
+ *
+ * If event.type == HMM_COPY_FROM_DEVICE then device driver must first
+ * write protect the range then schedule the copy, then update its page
+ * table to use the new system memory given the dst array. Some device
+ * can perform all this in an atomic fashion from device point of view.
+ * The device driver must also free the device memory once the copy is
+ * done.
+ *
+ * Device driver must not fail lightly, any failure result in device
+ * process being kill and CPU page table set to HWPOISON entry.
+ *
+ * Note that device driver must clear the valid bit of the dst entry it
+ * failed to copy.
+ *
+ * On failure the mirror will be kill by HMM which will do a HMM_MUNMAP
+ * invalidation of all the memory when this happen the device driver
+ * can free the device memory.
+ *
+ * Note also that there can be hole in the range being copied ie some
+ * entry of dst array will not have the valid bit set, device driver
+ * must simply ignore non valid entry.
+ *
+ * Finaly device driver must set the dirty bit for each page that was
+ * modified since it was copied inside the device memory. This must be
+ * conservative ie if device can not determine that with certainty then
+ * it must set the dirty bit unconditionally.
+ *
+ * Return 0 on success, error value otherwise :
+ * -ENOMEM Not enough memory for performing the operation.
+ * -EIO Some input/output error with the device.
+ *
+ * All other return value trigger warning and are transformed to -EIO.
+ */
+ int (*copy_from_device)(struct hmm_mirror *mirror,
+ const struct hmm_event *event,
+ dma_addr_t *dst,
+ unsigned long start,
+ unsigned long end);
+
+ /* copy_to_device() - copy to device memory from system memory.
+ *
+ * @mirror: The mirror that link process address space with the device.
+ * @event: The event that triggered the copy.
+ * @dst: Array containing hmm_pte of destination memory.
+ * @start: Start address of the range (sub-range of event) to copy.
+ * @end: End address of the range (sub-range of event) to copy.
+ * Returns: 0 on success, error code otherwise {-ENOMEM, -EIO}.
+ *
+ * Called when migrating memory from system memory to device memory.
+ * The dst array is empty, all of its entry are equal to zero. Device
+ * driver must allocate the device memory and populate each entry using
+ * hmm_pte_from_device_pfn() only the valid device bit and hardware
+ * specific bit will be preserve (write and dirty will be taken from
+ * the original entry inside the mirror page table). It is advice to
+ * set the device pfn to match the physical address of device memory
+ * being use. The event.etype will be equals to HMM_COPY_TO_DEVICE.
+ *
+ * Device driver that can atomically copy a page and update its page
+ * table entry to point to the device memory can do that. Partial
+ * failure is allowed, entry that have not been migrated must have
+ * the HMM_PTE_VALID_DEV bit clear inside the dst array. HMM will
+ * update the CPU page table of failed entry to point back to the
+ * system page.
+ *
+ * Note that device driver is responsible for allocating and freeing
+ * the device memory and properly updating to dst array entry with
+ * the allocated device memory.
+ *
+ * Return 0 on success, error value otherwise :
+ * -ENOMEM Not enough memory for performing the operation.
+ * -EIO Some input/output error with the device.
+ *
+ * All other return value trigger warning and are transformed to -EIO.
+ * Errors means that the migration is aborted. So in case of partial
+ * failure if device do not want to fully abort it must return 0.
+ * Device driver can update device page table only if it knows it will
+ * not return failure.
+ */
+ int (*copy_to_device)(struct hmm_mirror *mirror,
+ const struct hmm_event *event,
+ dma_addr_t *dst,
+ unsigned long start,
+ unsigned long end);
};


diff --git a/mm/hmm.c b/mm/hmm.c
index e4585b7..9dbb1e43 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -87,6 +87,8 @@ static inline int hmm_event_init(struct hmm_event *event,
case HMM_ISDIRTY:
case HMM_DEVICE_RFAULT:
case HMM_DEVICE_WFAULT:
+ case HMM_COPY_TO_DEVICE:
+ case HMM_COPY_FROM_DEVICE:
break;
case HMM_FORK:
case HMM_WRITE_PROTECT:
--
1.9.3


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