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mm/hmm: improve and rename hmm_vma_fault() to hmm_range_fault()
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Minor optimization around hmm_pte_need_fault().  Rename for consistency
between code, comments and documentation.  Also improves the comments on
all the possible returns values.  Improve the function by returning the
number of populated entries in pfns array.

Link: http://lkml.kernel.org/r/20190403193318.16478-6-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Jérôme Glisse authored and Linus Torvalds committed May 14, 2019
1 parent 25f23a0 commit 7323161
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Showing 3 changed files with 52 additions and 60 deletions.
8 changes: 1 addition & 7 deletions Documentation/vm/hmm.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -190,13 +190,7 @@ When the device driver wants to populate a range of virtual addresses, it can
use either::

long hmm_range_snapshot(struct hmm_range *range);
int hmm_vma_fault(struct vm_area_struct *vma,
struct hmm_range *range,
unsigned long start,
unsigned long end,
hmm_pfn_t *pfns,
bool write,
bool block);
long hmm_range_fault(struct hmm_range *range, bool block);

The first one (hmm_range_snapshot()) will only fetch present CPU page table
entries and will not trigger a page fault on missing or non-present entries.
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13 changes: 12 additions & 1 deletion include/linux/hmm.h
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Original file line number Diff line number Diff line change
Expand Up @@ -391,7 +391,18 @@ bool hmm_vma_range_done(struct hmm_range *range);
*
* See the function description in mm/hmm.c for further documentation.
*/
int hmm_vma_fault(struct hmm_range *range, bool block);
long hmm_range_fault(struct hmm_range *range, bool block);

/* This is a temporary helper to avoid merge conflict between trees. */
static inline int hmm_vma_fault(struct hmm_range *range, bool block)
{
long ret = hmm_range_fault(range, block);
if (ret == -EBUSY)
ret = -EAGAIN;
else if (ret == -EAGAIN)
ret = -EBUSY;
return ret < 0 ? ret : 0;
}

/* Below are for HMM internal use only! Not to be used by device driver! */
void hmm_mm_destroy(struct mm_struct *mm);
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91 changes: 39 additions & 52 deletions mm/hmm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -340,13 +340,13 @@ static int hmm_vma_do_fault(struct mm_walk *walk, unsigned long addr,
flags |= write_fault ? FAULT_FLAG_WRITE : 0;
ret = handle_mm_fault(vma, addr, flags);
if (ret & VM_FAULT_RETRY)
return -EBUSY;
return -EAGAIN;
if (ret & VM_FAULT_ERROR) {
*pfn = range->values[HMM_PFN_ERROR];
return -EFAULT;
}

return -EAGAIN;
return -EBUSY;
}

static int hmm_pfns_bad(unsigned long addr,
Expand All @@ -372,7 +372,7 @@ static int hmm_pfns_bad(unsigned long addr,
* @fault: should we fault or not ?
* @write_fault: write fault ?
* @walk: mm_walk structure
* Returns: 0 on success, -EAGAIN after page fault, or page fault error
* Returns: 0 on success, -EBUSY after page fault, or page fault error
*
* This function will be called whenever pmd_none() or pte_none() returns true,
* or whenever there is no page directory covering the virtual address range.
Expand All @@ -395,12 +395,12 @@ static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end,

ret = hmm_vma_do_fault(walk, addr, write_fault,
&pfns[i]);
if (ret != -EAGAIN)
if (ret != -EBUSY)
return ret;
}
}

return (fault || write_fault) ? -EAGAIN : 0;
return (fault || write_fault) ? -EBUSY : 0;
}

static inline void hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
Expand Down Expand Up @@ -531,11 +531,11 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
uint64_t orig_pfn = *pfn;

*pfn = range->values[HMM_PFN_NONE];
cpu_flags = pte_to_hmm_pfn_flags(range, pte);
hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
&fault, &write_fault);
fault = write_fault = false;

if (pte_none(pte)) {
hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0,
&fault, &write_fault);
if (fault || write_fault)
goto fault;
return 0;
Expand Down Expand Up @@ -574,14 +574,18 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
hmm_vma_walk->last = addr;
migration_entry_wait(vma->vm_mm,
pmdp, addr);
return -EAGAIN;
return -EBUSY;
}
return 0;
}

/* Report error for everything else */
*pfn = range->values[HMM_PFN_ERROR];
return -EFAULT;
} else {
cpu_flags = pte_to_hmm_pfn_flags(range, pte);
hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
&fault, &write_fault);
}

if (fault || write_fault)
Expand Down Expand Up @@ -632,7 +636,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
if (fault || write_fault) {
hmm_vma_walk->last = addr;
pmd_migration_entry_wait(vma->vm_mm, pmdp);
return -EAGAIN;
return -EBUSY;
}
return 0;
} else if (!pmd_present(pmd))
Expand Down Expand Up @@ -860,53 +864,34 @@ bool hmm_vma_range_done(struct hmm_range *range)
EXPORT_SYMBOL(hmm_vma_range_done);

/*
* hmm_vma_fault() - try to fault some address in a virtual address range
* hmm_range_fault() - try to fault some address in a virtual address range
* @range: range being faulted
* @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem)
* Returns: 0 success, error otherwise (-EAGAIN means mmap_sem have been drop)
* Returns: number of valid pages in range->pfns[] (from range start
* address). This may be zero. If the return value is negative,
* then one of the following values may be returned:
*
* -EINVAL invalid arguments or mm or virtual address are in an
* invalid vma (ie either hugetlbfs or device file vma).
* -ENOMEM: Out of memory.
* -EPERM: Invalid permission (for instance asking for write and
* range is read only).
* -EAGAIN: If you need to retry and mmap_sem was drop. This can only
* happens if block argument is false.
* -EBUSY: If the the range is being invalidated and you should wait
* for invalidation to finish.
* -EFAULT: Invalid (ie either no valid vma or it is illegal to access
* that range), number of valid pages in range->pfns[] (from
* range start address).
*
* This is similar to a regular CPU page fault except that it will not trigger
* any memory migration if the memory being faulted is not accessible by CPUs.
* any memory migration if the memory being faulted is not accessible by CPUs
* and caller does not ask for migration.
*
* On error, for one virtual address in the range, the function will mark the
* corresponding HMM pfn entry with an error flag.
*
* Expected use pattern:
* retry:
* down_read(&mm->mmap_sem);
* // Find vma and address device wants to fault, initialize hmm_pfn_t
* // array accordingly
* ret = hmm_vma_fault(range, write, block);
* switch (ret) {
* case -EAGAIN:
* hmm_vma_range_done(range);
* // You might want to rate limit or yield to play nicely, you may
* // also commit any valid pfn in the array assuming that you are
* // getting true from hmm_vma_range_monitor_end()
* goto retry;
* case 0:
* break;
* case -ENOMEM:
* case -EINVAL:
* case -EPERM:
* default:
* // Handle error !
* up_read(&mm->mmap_sem)
* return;
* }
* // Take device driver lock that serialize device page table update
* driver_lock_device_page_table_update();
* hmm_vma_range_done(range);
* // Commit pfns we got from hmm_vma_fault()
* driver_unlock_device_page_table_update();
* up_read(&mm->mmap_sem)
*
* YOU MUST CALL hmm_vma_range_done() AFTER THIS FUNCTION RETURN SUCCESS (0)
* BEFORE FREEING THE range struct OR YOU WILL HAVE SERIOUS MEMORY CORRUPTION !
*
* YOU HAVE BEEN WARNED !
*/
int hmm_vma_fault(struct hmm_range *range, bool block)
long hmm_range_fault(struct hmm_range *range, bool block)
{
struct vm_area_struct *vma = range->vma;
unsigned long start = range->start;
Expand Down Expand Up @@ -978,7 +963,8 @@ int hmm_vma_fault(struct hmm_range *range, bool block)
do {
ret = walk_page_range(start, range->end, &mm_walk);
start = hmm_vma_walk.last;
} while (ret == -EAGAIN);
/* Keep trying while the range is valid. */
} while (ret == -EBUSY && range->valid);

if (ret) {
unsigned long i;
Expand All @@ -988,6 +974,7 @@ int hmm_vma_fault(struct hmm_range *range, bool block)
range->end);
hmm_vma_range_done(range);
hmm_put(hmm);
return ret;
} else {
/*
* Transfer hmm reference to the range struct it will be drop
Expand All @@ -997,9 +984,9 @@ int hmm_vma_fault(struct hmm_range *range, bool block)
range->hmm = hmm;
}

return ret;
return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
}
EXPORT_SYMBOL(hmm_vma_fault);
EXPORT_SYMBOL(hmm_range_fault);
#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */


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