Messages in this thread | | | Date | Sun, 25 Jan 2015 15:16:44 +0200 | From | Oded Gabbay <> | Subject | Re: [PATCH 2/2] iommu/amd: use handle_mm_fault directly v2 |
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On 11/13/2014 12:10 AM, Jesse Barnes wrote: > This could be useful for debug in the future if we want to track > major/minor faults more closely, and also avoids the put_page trick we > used with gup. > > In order to do this, we also track the task struct in the PASID state > structure. This lets us update the appropriate task stats after the > fault has been handled, and may aid with debug in the future as well. > > v2: drop task accounting; GPU activity may have been submitted by a > different thread than the one binding the PASID (Joerg) > > Tested-by: Oded Gabbay<oded.gabbay@amd.com> > Signed-off-by: Jesse Barnes<jbarnes@virtuousgeek.org>
Hi Jesse,
I know I tested your patch a few months ago, but we have a new feature (still internally) in the driver, which has some conflicts with this patch.
Our feature is basically doing "exception handling" by registering a callback function with the iommu driver in inv_ppr_cb.
Now, with the old code (we used 3.17.2 until a few days ago), this callback function was called in, at least, three use-cases (which we are testing):
(1) Writing to a "bad" system memory address, which is *not* in the process's memory address space.
(2) Writing to a read-only page, which is inside the process's memory address space
(3) Reading from a page without permissions, which is inside the process's memory address space
With the new code (3.19-rc5), this callback is only called in the first use-case, while (2) and (3) are handled in handle_mm_fault(), which is now called from do_fault. The return value of handle_mm_fault() is 0, so handle_fault_error() is not called and amdkfd doesn't get notification, hence our test fails.
This is a problem for us as we want to propagate these exceptions to the user space HSA runtime, so it could handle them.
I have 2 questions:
1. Why don't we call inv_ppr_cb() in any case ? 2. How come handle_mm_fault() returns 0 in cases (2) and (3) ? Or in other words, what is considered to be a success in handle_mm_fault() and is it visible to the user-space process ?
Thanks,
Oded
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