Re: [PATCH] mm/secretmem: disable under HIGHMEM

[David Hildenbrand (Arm)]

On 7/15/26 16:58, Mike Rapoport wrote:
> On Wed, Jul 15, 2026 at 03:49:39PM +0200, David Hildenbrand (Arm) wrote:
>> On 7/15/26 15:44, Mike Rapoport wrote:
>>>
>>> No, I mean what Brendan's patch did:
>>>
>>>  config SECRETMEM
>>>         default y
>>>         bool "Enable memfd_secret() system call" if EXPERT
>>> -       depends on ARCH_HAS_SET_DIRECT_MAP
>>> +       depends on ARCH_HAS_SET_DIRECT_MAP && !HIGHMEM
>>>
>>> We can change gfp_mask as well for the sake of pedancy
>>
>> Why not change the gfp mask only then?
> 
> Citing myself from a few emails back: 
> 
>>> But still with kmap() and friends not being an NOP the promise "kernel does
>>> not map this memory" does not hold.

So you're saying that kmap() would perform a mapping for a non-highmem page?

static inline void *kmap(struct page *page)
{
	void *addr;

	might_sleep();
	if (!PageHighMem(page))
		addr = page_address(page);
	else
		addr = kmap_high(page);
	kmap_flush_tlb((unsigned long)addr);
	return addr;
}

I'm missing something important.

-- 
Cheers,

David