On Sun, 25 Jan 2015 15:16:44 +0200 Oded Gabbay <oded.gab...@amd.com> wrote:
> > > 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.gab...@amd.com> > > Signed-off-by: Jesse Barnes<jbar...@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 ? We do if we fail to allocate the vma or it's in the wrong location, but we could extend the do_fault() handling to do it in more cases. > 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 ? handle_mm_fault() is somewhat of a low level function. We can catch more cases in our own do_fault() code if we need to. The x86 __do_page_fault is probably a good reference. I mainly tried to match existing behavior when I added the handle_mm_fault(), but may have missed stuff. As I said, we can extend our do_fault() to handle all the cases we want prior to calling handle_mm_fault(). Thanks, -- Jesse Barnes, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
