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authorJason Gunthorpe <jgg@mellanox.com>2019-11-12 16:22:30 -0400
committerJason Gunthorpe <jgg@mellanox.com>2019-11-23 19:56:45 -0400
commita22dd506400d0f4784ad596f073b9eb5ed7c6a2a (patch)
tree55e0716e1e78ff34c4ce515671a6ae9de80741a0 /Documentation/vm
parent81fa1af31b5d79047821def6abdcb97a735d8a52 (diff)
mm/hmm: remove hmm_mirror and related
The only two users of this are now converted to use mmu_interval_notifier, delete all the code and update hmm.rst. Link: https://lore.kernel.org/r/20191112202231.3856-14-jgg@ziepe.ca Reviewed-by: Jérôme Glisse <jglisse@redhat.com> Tested-by: Ralph Campbell <rcampbell@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Diffstat (limited to 'Documentation/vm')
-rw-r--r--Documentation/vm/hmm.rst105
1 files changed, 24 insertions, 81 deletions
diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 0a5960beccf7..893a8ba0e9fe 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -147,49 +147,16 @@ Address space mirroring implementation and API
Address space mirroring's main objective is to allow duplication of a range of
CPU page table into a device page table; HMM helps keep both synchronized. A
device driver that wants to mirror a process address space must start with the
-registration of an hmm_mirror struct::
-
- int hmm_mirror_register(struct hmm_mirror *mirror,
- struct mm_struct *mm);
-
-The mirror struct has a set of callbacks that are used
-to propagate CPU page tables::
-
- struct hmm_mirror_ops {
- /* release() - release hmm_mirror
- *
- * @mirror: pointer to struct hmm_mirror
- *
- * This is called when the mm_struct is being released. The callback
- * must ensure that all access to any pages obtained from this mirror
- * is halted before the callback returns. All future access should
- * fault.
- */
- void (*release)(struct hmm_mirror *mirror);
-
- /* sync_cpu_device_pagetables() - synchronize page tables
- *
- * @mirror: pointer to struct hmm_mirror
- * @update: update information (see struct mmu_notifier_range)
- * Return: -EAGAIN if update.blockable false and callback need to
- * block, 0 otherwise.
- *
- * This callback ultimately originates from mmu_notifiers when the CPU
- * page table is updated. The device driver must update its page table
- * in response to this callback. The update argument tells what action
- * to perform.
- *
- * The device driver must not return from this callback until the device
- * page tables are completely updated (TLBs flushed, etc); this is a
- * synchronous call.
- */
- int (*sync_cpu_device_pagetables)(struct hmm_mirror *mirror,
- const struct hmm_update *update);
- };
-
-The device driver must perform the update action to the range (mark range
-read only, or fully unmap, etc.). The device must complete the update before
-the driver callback returns.
+registration of a mmu_interval_notifier::
+
+ mni->ops = &driver_ops;
+ int mmu_interval_notifier_insert(struct mmu_interval_notifier *mni,
+ unsigned long start, unsigned long length,
+ struct mm_struct *mm);
+
+During the driver_ops->invalidate() callback the device driver must perform
+the update action to the range (mark range read only, or fully unmap,
+etc.). The device must complete the update before the driver callback returns.
When the device driver wants to populate a range of virtual addresses, it can
use::
@@ -216,70 +183,46 @@ The usage pattern is::
struct hmm_range range;
...
+ range.notifier = &mni;
range.start = ...;
range.end = ...;
range.pfns = ...;
range.flags = ...;
range.values = ...;
range.pfn_shift = ...;
- hmm_range_register(&range, mirror);
- /*
- * Just wait for range to be valid, safe to ignore return value as we
- * will use the return value of hmm_range_fault() below under the
- * mmap_sem to ascertain the validity of the range.
- */
- hmm_range_wait_until_valid(&range, TIMEOUT_IN_MSEC);
+ if (!mmget_not_zero(mni->notifier.mm))
+ return -EFAULT;
again:
+ range.notifier_seq = mmu_interval_read_begin(&mni);
down_read(&mm->mmap_sem);
ret = hmm_range_fault(&range, HMM_RANGE_SNAPSHOT);
if (ret) {
up_read(&mm->mmap_sem);
- if (ret == -EBUSY) {
- /*
- * No need to check hmm_range_wait_until_valid() return value
- * on retry we will get proper error with hmm_range_fault()
- */
- hmm_range_wait_until_valid(&range, TIMEOUT_IN_MSEC);
- goto again;
- }
- hmm_range_unregister(&range);
+ if (ret == -EBUSY)
+ goto again;
return ret;
}
+ up_read(&mm->mmap_sem);
+
take_lock(driver->update);
- if (!hmm_range_valid(&range)) {
+ if (mmu_interval_read_retry(&ni, range.notifier_seq) {
release_lock(driver->update);
- up_read(&mm->mmap_sem);
goto again;
}
- // Use pfns array content to update device page table
+ /* Use pfns array content to update device page table,
+ * under the update lock */
- hmm_range_unregister(&range);
release_lock(driver->update);
- up_read(&mm->mmap_sem);
return 0;
}
The driver->update lock is the same lock that the driver takes inside its
-sync_cpu_device_pagetables() callback. That lock must be held before calling
-hmm_range_valid() to avoid any race with a concurrent CPU page table update.
-
-HMM implements all this on top of the mmu_notifier API because we wanted a
-simpler API and also to be able to perform optimizations latter on like doing
-concurrent device updates in multi-devices scenario.
-
-HMM also serves as an impedance mismatch between how CPU page table updates
-are done (by CPU write to the page table and TLB flushes) and how devices
-update their own page table. Device updates are a multi-step process. First,
-appropriate commands are written to a buffer, then this buffer is scheduled for
-execution on the device. It is only once the device has executed commands in
-the buffer that the update is done. Creating and scheduling the update command
-buffer can happen concurrently for multiple devices. Waiting for each device to
-report commands as executed is serialized (there is no point in doing this
-concurrently).
-
+invalidate() callback. That lock must be held before calling
+mmu_interval_read_retry() to avoid any race with a concurrent CPU page table
+update.
Leverage default_flags and pfn_flags_mask
=========================================