On 01/06/26 5:39 am, Balbir Singh wrote:
> On 5/30/26 18:54, Dev Jain wrote:
>> To cover pagemap paths scanning PMD entries, add assertions to check
>> whether a device-private PMD entry has the correct pagemap information -
>> the PM_SWAP bit must be on in the pagemap entry. Before that, we must
>> assert through HMM_DMIRROR_SNAPSHOT snapshot that the leaf entry is
>> at PMD level and not PTE level.
>>
>> Signed-off-by: Dev Jain <[email protected]>
>> ---
>> tools/testing/selftests/mm/hmm-tests.c | 29 ++++++++++++++++++++++++++
>> 1 file changed, 29 insertions(+)
>>
>> diff --git a/tools/testing/selftests/mm/hmm-tests.c
>> b/tools/testing/selftests/mm/hmm-tests.c
>> index e1c8a679a4cf3..d09d4a9081de1 100644
>> --- a/tools/testing/selftests/mm/hmm-tests.c
>> +++ b/tools/testing/selftests/mm/hmm-tests.c
>> @@ -2276,8 +2276,11 @@ TEST_F(hmm, migrate_anon_huge_fault)
>> unsigned long npages;
>> unsigned long size;
>> unsigned long i;
>> + unsigned char *m;
>> + uint64_t entry;
>> void *old_ptr;
>> void *map;
>> + int pagemap_fd;
>> int *ptr;
>> int ret;
>>
>> @@ -2318,6 +2321,32 @@ TEST_F(hmm, migrate_anon_huge_fault)
>> for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
>> ASSERT_EQ(ptr[i], i);
>>
>> + if (!hmm_is_coherent_type(variant->device_number)) {
>> + ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_SNAPSHOT,
>> + buffer, npages);
>> + ASSERT_EQ(ret, 0);
>> + ASSERT_EQ(buffer->cpages, npages);
>> +
>> + m = buffer->mirror;
>> + for (i = 0; i < npages; ++i)
>> + ASSERT_EQ(m[i], HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL |
>> + HMM_DMIRROR_PROT_WRITE |
>> + HMM_DMIRROR_PROT_PMD);
>
> madvise(..., MADV_HUGEPAGE) is not sufficient to guarantee that the allocation
> was indeed converted to THP. Might be worth using the kpageflags interface
> (but that
> requires elevated privileges) and then KPF_THP? Otherwise the
> HMM_DMIRROR_PROT_PMD
> can be a miss from time to time. One other option is not to assert, but to
> check
> and inform?
I'll then use the existing check_huge_anon() to assert that a PMD THP got
allocated.
>
>> +
>> + pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
>> + ASSERT_GE(pagemap_fd, 0);
>> +
>> + for (i = 0; i < npages; ++i) {
>> + entry = pagemap_get_entry(pagemap_fd,
>> + (char *)buffer->ptr + i *
>> self->page_size);
>> +
>
> If this is a THP entry, do we have valid pagemap entries for offset of i *
> page_size?
Yep we do, see the populate_pagemap label in pagemap_pmd_range_thp.
>
>> + ASSERT_NE(entry & PM_SWAP, 0);
>> + ASSERT_EQ(entry & PM_PRESENT, 0);
>
> Nit: You can use PAGEMAP_PRESENT()
Okay.
>
>> + }
>> +
>> + close(pagemap_fd);
>> + }
>> +
>> /* Fault pages back to system memory and check them. */
>> for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
>> ASSERT_EQ(ptr[i], i);
>
> Balbir Singh
