LinuxKPI: switch mallocarray to an lpi implementation using __kmalloc()

[bz]

Summary

With mallocarray() we cannot guarantee that any size larger than
PAGE_SIZE will be contiguous. Switch to use the internal __kmalloc()
implementation which now does provide that guarantee.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days

[emaste]

OK

[bz]

Also change the (internal) mallocarray() calls in linux_compat.c to lkpi_mallocarray()
given we are using the LinuxKPI malloc type (M_KMALLOC) there already; better for
consistency.

[bz]

@jhb any comments?

[emaste]

Probably fine to go in

[manu]

I'm not a fan of this, mallocarray is a OpenBSD thing, not a Linux thing, I don't see why we should have an lkpi implementation.

[bz]

It's a helper function; because we do use mallocarray internally and it doesn't go by Linux guarantees on memory being physically contiguous in some cases. I can replace all the mallocarray calls directly with __kmalloc() but that just makes it harder to maintain in many places rather one. We can name this whatever we want it to be if you do not like the name...

[jhb]

This seems certainly fine. This is the semantics required for kcalloc and kmalloc_array

sys/compat/linuxkpi/common/include/linux/slab.h

116–117

This isn't enforcing contigmalloc for size > PAGE_SIZE?

148–149

Similarly, this also needs to enforce contigmalloc.

I would be tempted to implement the *calloc functions by setting the ZERO flag and then calling the malloc_array function, e.g.:

kcalloc_node()
{
   flags |= __GFP_ZERO;
   return kmalloc_array_node(...)
}

Same can be true for kcalloc() calling kmalloc_array(). Then, you could just have the ABI symbols be lkpi_kmalloc_array and lkpi_kmalloc_array_node as you do today for kmalloc. This also suggests btw that you need to add a shim for kmalloc_node that uses contigmalloc for larger sizes.

sys/compat/linuxkpi/common/src/linux_compat.c

2770–2771

Maybe use just use the kmalloc_array here instead and elsewhere in this file, then you aren't exposing the internal symbol more widely?

[bz]

Drop lkpi_mallocarray as requested by @manu.

Add a lkpi___kmalloc_node() in parallel to lkpi___kmalloc() which does the if and the actual
allocation in a C file so we do not spread malloc calls in inline functions anymore.

Follow the path suggested by @jhb which works out nicely:
Use two former functions as base for their *_array functions. Use those as base for the
remaing wrappers.

Switch to kmalloc_array() inseatd of our lkpi_ version to avoid further exposure of it.

Add comments about realloc as it seems kern_malloc.c does not handle that yet and we need
to have a chat about it.

[bz]

sys/compat/linuxkpi/common/src/linux_slab.c

230

@jhb, @emaste, This should be <= as well, correct?

[bz]

I really shouldn't code with a fever. Need to reshuffle the functions so they will compile. Also )

[bz]

Make compile as well fixing order and ()