On Wed, Feb 28, 2018 at 10:06:20PM +0200, Igor Stoppa wrote: > Detailed documentation about the protectable memory allocator. > > Signed-off-by: Igor Stoppa <igor.sto...@huawei.com> > --- > Documentation/core-api/index.rst | 1 + > Documentation/core-api/pmalloc.rst | 111 > +++++++++++++++++++++++++++++++++++++ > 2 files changed, 112 insertions(+) > create mode 100644 Documentation/core-api/pmalloc.rst > > diff --git a/Documentation/core-api/index.rst > b/Documentation/core-api/index.rst > index c670a8031786..8f5de42d6571 100644 > --- a/Documentation/core-api/index.rst > +++ b/Documentation/core-api/index.rst > @@ -25,6 +25,7 @@ Core utilities > genalloc > errseq > printk-formats > + pmalloc > > Interfaces for kernel debugging > =============================== > diff --git a/Documentation/core-api/pmalloc.rst > b/Documentation/core-api/pmalloc.rst > new file mode 100644 > index 000000000000..8fb9c9d3171b > --- /dev/null > +++ b/Documentation/core-api/pmalloc.rst > @@ -0,0 +1,111 @@ > +.. SPDX-License-Identifier: GPL-2.0
Please add a label to allow cross-referencing > + > +Protectable memory allocator > +============================ > + > +Purpose > +------- > + > +The pmalloc library is meant to provide R/O status to data that, for some > +reason, could neither be declared as constant, nor could it take advantage > +of the qualifier __ro_after_init, but is write-once and read-only in spirit. > +It protects data from both accidental and malicious overwrites. > + > +Example: A policy that is loaded from userspace. > + > + > +Concept > +------- > + > +pmalloc builds on top of genalloc, using the same concept of memory pools. It would be nice to add a label to genalloc.rst and reference it here: diff --git a/Documentation/core-api/genalloc.rst b/Documentation/core-api/genalloc.rst index 6b38a39fab24..983fa94f999c 100644 --- a/Documentation/core-api/genalloc.rst +++ b/Documentation/core-api/genalloc.rst @@ -1,3 +1,5 @@ +.. _genalloc: + The genalloc/genpool subsystem ============================== > + > +The value added by pmalloc is that now the memory contained in a pool can > +become R/O, for the rest of the life of the pool. > + IMHO, "read only" looks better than R/O > +Different kernel drivers and threads can use different pools, for finer > +control of what becomes R/O and when. And for improved lockless concurrency. > + > + > +Caveats > +------- > + > +- Memory freed while a pool is not yet protected will be reused. > + > +- Once a pool is protected, it's not possible to allocate any more memory > + from it. > + > +- Memory "freed" from a protected pool indicates that such memory is not > + in use anymore by the requester; however, it will not become available > + for further use, until the pool is destroyed. > + > +- pmalloc does not provide locking support with respect to allocating vs > + protecting an individual pool, for performance reasons. > + It is recommended not to share the same pool between unrelated functions. > + Should sharing be a necessity, the user of the shared pool is expected > + to implement locking for that pool. > + > +- pmalloc uses genalloc to optimize the use of the space it allocates > + through vmalloc. Some more TLB entries will be used, however less than > + in the case of using vmalloc directly. The exact number depends on the > + size of each allocation request and possible slack. > + > +- Considering that not much data is supposed to be dynamically allocated > + and then marked as read-only, it shouldn't be an issue that the address > + range for pmalloc is limited, on 32-bit systems. > + > +- Regarding SMP systems, the allocations are expected to happen mostly > + during an initial transient, after which there should be no more need to > + perform cross-processor synchronizations of page tables. > + > +- To facilitate the conversion of existing code to pmalloc pools, several > + helper functions are provided, mirroring their kmalloc counterparts. > + > + > +Use > +--- > + > +The typical sequence, when using pmalloc, is: > + > +1. create a pool Can we use #. instead of numbers for the numbered list items? > +.. kernel-doc:: include/linux/pmalloc.h > + :functions: pmalloc_create_pool > + > +2. [optional] pre-allocate some memory in the pool > + > +.. kernel-doc:: include/linux/pmalloc.h > + :functions: pmalloc_prealloc Maybe it's better to have a short reference to the function and keep all the elaborate descriptions in the API section? For instance, something like diff --git a/Documentation/core-api/pmalloc.rst b/Documentation/core-api/pmalloc.rst @@ -68,8 +70,7 @@ The typical sequence, when using pmalloc, is: 1. create a pool -.. kernel-doc:: include/linux/pmalloc.h - :functions: pmalloc_create_pool + :c:func:`pmalloc_create_pool` > +3. issue one or more allocation requests to the pool with locking as needed > + > +.. kernel-doc:: include/linux/pmalloc.h > + :functions: pmalloc > + > +.. kernel-doc:: include/linux/pmalloc.h > + :functions: pzalloc > + > +4. initialize the memory obtained with desired values > + > +5. [optional] iterate over points 3 & 4 as needed > + > +6. write-protect the pool > + > +.. kernel-doc:: include/linux/pmalloc.h > + :functions: pmalloc_protect_pool > + > +7. use in read-only mode the handles obtained through the allocations > + > +8. [optional] release all the memory allocated > + > +.. kernel-doc:: include/linux/pmalloc.h > + :functions: pfree > + > +9. [optional, but depends on point 8] destroy the pool > + > +.. kernel-doc:: include/linux/pmalloc.h > + :functions: pmalloc_destroy_pool > + > +API > +--- > + > +.. kernel-doc:: include/linux/pmalloc.h > -- > 2.14.1 > -- Sincerely yours, Mike.