Hi Mike,
On Thu, 2025-08-28 at 15:26 +0100, Mike Rapoport wrote:
> On Thu, Aug 28, 2025 at 09:39:19AM +0000, Roy, Patrick wrote:
>> Add AS_NO_DIRECT_MAP for mappings where direct map entries of folios are
>> set to not present . Currently, mappings that match this description are
>> secretmem mappings (memfd_secret()). Later, some guest_memfd
>> configurations will also fall into this category.
>>
>> Reject this new type of mappings in all locations that currently reject
>> secretmem mappings, on the assumption that if secretmem mappings are
>> rejected somewhere, it is precisely because of an inability to deal with
>> folios without direct map entries, and then make memfd_secret() use
>> AS_NO_DIRECT_MAP on its address_space to drop its special
>> vma_is_secretmem()/secretmem_mapping() checks.
>>
>> This drops a optimization in gup_fast_folio_allowed() where
>> secretmem_mapping() was only called if CONFIG_SECRETMEM=y. secretmem is
>> enabled by default since commit b758fe6df50d ("mm/secretmem: make it on
>> by default"), so the secretmem check did not actually end up elided in
>> most cases anymore anyway.
>>
>> Use a new flag instead of overloading AS_INACCESSIBLE (which is already
>> set by guest_memfd) because not all guest_memfd mappings will end up
>> being direct map removed (e.g. in pKVM setups, parts of guest_memfd that
>> can be mapped to userspace should also be GUP-able, and generally not
>> have restrictions on who can access it).
>>
>> Signed-off-by: Patrick Roy <roypat@xxxxxxxxxxxx>
>> ---
>> include/linux/pagemap.h | 16 ++++++++++++++++
>> include/linux/secretmem.h | 18 ------------------
>> lib/buildid.c | 4 ++--
>> mm/gup.c | 14 +++-----------
>> mm/mlock.c | 2 +-
>> mm/secretmem.c | 6 +-----
>> 6 files changed, 23 insertions(+), 37 deletions(-)
>>
>> diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h
>> index e918f96881f5..0ae1fb057b3d 100644
>> --- a/include/linux/secretmem.h
>> +++ b/include/linux/secretmem.h
>> @@ -4,28 +4,10 @@
>>
>> #ifdef CONFIG_SECRETMEM
>>
>> -extern const struct address_space_operations secretmem_aops;
>
> Please also make secretmem_aops static in mm/secretmem.c
Ack.
>> -static inline bool secretmem_mapping(struct address_space *mapping)
>> -{
>> - return mapping->a_ops == &secretmem_aops;
>> -}
>> -
>
> ...
>
>> diff --git a/mm/gup.c b/mm/gup.c
>> index adffe663594d..8c988e076e5d 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1234,7 +1234,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
>> if ((gup_flags & FOLL_SPLIT_PMD) && is_vm_hugetlb_page(vma))
>> return -EOPNOTSUPP;
>>
>> - if (vma_is_secretmem(vma))
>> + if (vma_is_no_direct_map(vma))
>> return -EFAULT;
>>
>> if (write) {
>> @@ -2751,7 +2751,6 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
>> {
>> bool reject_file_backed = false;
>> struct address_space *mapping;
>> - bool check_secretmem = false;
>> unsigned long mapping_flags;
>>
>> /*
>> @@ -2763,14 +2762,6 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
>> reject_file_backed = true;
>>
>> /* We hold a folio reference, so we can safely access folio fields. */
>> -
>> - /* secretmem folios are always order-0 folios. */
>> - if (IS_ENABLED(CONFIG_SECRETMEM) && !folio_test_large(folio))
>> - check_secretmem = true;
>> -
>> - if (!reject_file_backed && !check_secretmem)
>> - return true;
>> -
>> if (WARN_ON_ONCE(folio_test_slab(folio)))
>> return false;
>
> There's a check for hugetlb after this and a comment there mentions
> secretmem, please update that to "mapping with no direct map" or something
> like that.
Ack.
> --
> Sincerely yours,
> Mike.
Thanks,
Patrick
