Re: [RFC PATCH v7 02/13] mm: Add an allocator for CoCo shared memory

[Catalin Marinas <catalin.marinas@arm.com>]

On Wed, Sep 23, 2026 at 02:01:08PM +0530, Aneesh Kumar K.V wrote:
> I was pointed to this email thread:
> 
> https://lore.kernel.org/all/c25502d3-35c6-4281-a9ec-856f789fb1b4@arm.com
> 
> This makes a stronger case for having a CoCo shared memory allocator
> that captures all these restrictions. It also means that
> alloc_cc_shared_pages_node() needs:
> 
> 	if (WARN_ON_ONCE(!gfpflags_allow_blocking(gfp)))
> 		return -EINVAL;
> 
> 	might_sleep();

I think gfpflags_allow_blocking() is the wrong predicate. It checks for
__GFP_DIRECT_RECLAIM but we have callers like dma-buf which clear the
flag (see HIGH_ORDER_GFP). ITS allocations also use GFP_NOWAIT, so
they'll fail here.

I'd just keep a might_sleep() in cc_make_*() and ignore gfp flags
checking. Passing a no-blocking GFP flag doesn't necessarily mean the
caller cannot sleep. It might also happen early enough (like its_init())
not to care - __might_resched() skips the warning if SYSTEM_BOOTING.

-- 
Catalin