On 2020-05-01 11:20, Jason Gunthorpe wrote:
From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
hmm_vma_walk->last is supposed to be updated after every write to the
pfns, so that it can be returned by hmm_range_fault(). However, this is
not done consistently. Fortunately nothing checks the return code of
hmm_range_fault() for anything other than error.
More importantly last must be set before returning -EBUSY as it is used to
prevent reading an output pfn as an input flags when the loop restarts.
For clarity and simplicity make hmm_range_fault() return 0 or -ERRNO. Only
set last when returning -EBUSY.
Yes, this is also a nice simplification.
...
@@ -590,10 +580,13 @@ long hmm_range_fault(struct hmm_range *range)
return -EBUSY;
ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
&hmm_walk_ops, &hmm_vma_walk);
+ /*
+ * When -EBUSY is returned the loop restarts with
+ * hmm_vma_walk.last set to an address that has not been stored
+ * in pfns. All entries < last in the pfn array are set to their
+ * output, and all >= are still at their input values.
+ */
I'm glad you added that comment. This is much easier to figure out with
that in place. After poking around this patch and eventually understanding the
.last handling, I wondered if you might like this slightly tweaked wording
instead:
/*
* Each of the hmm_walk_ops routines returns -EBUSY if and only
* hmm_vma_walk.last has been set to an address that has not yet
* been stored in pfns. All entries < last in the pfn array are
* set to their output, and all >= are still at their input
* values.
*/
Either way,
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
thanks,
--
John Hubbard
NVIDIA
} while (ret == -EBUSY);
-
- if (ret)
- return ret;
- return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
+ return ret;
}
EXPORT_SYMBOL(hmm_range_fault);
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