Re: [PATCH v2 2/2] mm/hmm: add a test for cross device private faults

[Ralph Campbell <rcampbell@nvidia.com>]

On 7/26/22 14:03, John Hubbard wrote:
> On 7/25/22 11:36, Ralph Campbell wrote:
>> Add a simple test case for when hmm_range_fault() is called with the
>> HMM_PFN_REQ_FAULT flag and a device private PTE is found for a device
>> other than the hmm_range::dev_private_owner. This should cause the
>> page to be faulted back to system memory from the other device and the
>> PFN returned in the output array.
>>
>> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
>> ---
>>   tools/testing/selftests/vm/hmm-tests.c | 14 ++++++++++++--
>>   1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/vm/hmm-tests.c 
>> b/tools/testing/selftests/vm/hmm-tests.c
>> index 203323967b50..a5ce7cc2e7aa 100644
>> --- a/tools/testing/selftests/vm/hmm-tests.c
>> +++ b/tools/testing/selftests/vm/hmm-tests.c
>> @@ -1520,9 +1520,19 @@ TEST_F(hmm2, double_map)
>>       for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
>>           ASSERT_EQ(ptr[i], i);
>>   -    /* Punch a hole after the first page address. */
>> -    ret = munmap(buffer->ptr + self->page_size, self->page_size);
>
> If this removal was intentional, then it should be mentioned in the
> commit log.

Yes. It does nothing, probably a copy & paste error.
I'll update the description and send a v3.

>
>> +    /* Migrate pages to device 1 and try to read from device 0. */
>> +    ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, 
>> npages);
>> +    ASSERT_EQ(ret, 0);
>> +    ASSERT_EQ(buffer->cpages, npages);
>> +
>> +    ret = hmm_dmirror_cmd(self->fd0, HMM_DMIRROR_READ, buffer, npages);
>>       ASSERT_EQ(ret, 0);
>> +    ASSERT_EQ(buffer->cpages, npages);
>> +    ASSERT_EQ(buffer->faults, 1);
>> +
>> +    /* Check what device 0 read. */
>> +    for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
>> +        ASSERT_EQ(ptr[i], i);
>
> I'm assuming that your testing shows that this fails without patch 1,
> and succeeds with patch 1 applied? Apologies for such an obvious
> question... :)

Yes. Without the patch, the ASSERT_EQ(ret, 0) would trigger.
With the patch, ASSERT_EQ(buffer->faults, 1) verifies that the pages
were faulted in from device 1 when device 0 tries to read them.