On 2/25/25 17:52, David Hildenbrand wrote:
> On 21.02.25 17:07, Patrick Roy 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.
>>
>> 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>
>> ---
>
> ...
>
>> static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
>> {
>> return mapping->gfp_mask;
>> diff --git a/lib/buildid.c b/lib/buildid.c
>> index c4b0f376fb34..80b5d805067f 100644
>> --- a/lib/buildid.c
>> +++ b/lib/buildid.c
>> @@ -65,8 +65,8 @@ static int freader_get_folio(struct freader *r, loff_t file_off)
>>
>> freader_put_folio(r);
>>
>> - /* reject secretmem folios created with memfd_secret() */
>> - if (secretmem_mapping(r->file->f_mapping))
>> + /* reject secretmem folios created with memfd_secret() or guest_memfd() */
>> + if (secretmem_mapping(r->file->f_mapping) || mapping_no_direct_map(r->file->f_mapping))
>> return -EFAULT;
>
> Maybe I'm missing it, but why do we have to special-case secretmem with
> that at all anymore?
>
> Couldn't we just let secretmem set AS_NO_DIRECT_MAP as well, and convert
> all/most secretmem specific stuff to check AS_NO_DIRECT_MAP as well?
That's done in patch 02. But yeah, squashing them together would reduce some
churn. I guess because it removes some !IS_ENABLED(CONFIG_SECRETMEM)
optimizations, a separate change for review was preferred.
