On 4/10/23 00:39, John Hubbard wrote:
pfn_to_page(x) for values 0xc00_0000 < x < 0x1000_0000 will produce a
kernel VA that points outside the region set aside for the vmemmap.
This region is currently unused, but that will likely change soon.
I tentatively think I'm in this case right now. Because there is no wrap
around happening in my particular config, which is CONFIG_ARM64_VA_BITS
== 48, and PAGE_SIZE == 4KB and sizeof(struct page) == 64 (details
below).
Correction, actually it *is* wrapping around, and ending up as a bogus
user space address, as you said it would when being above the range:
page_to_pfn(0xffffffffaee00000): 0x0000000ffec38000
It occurs to me that ZONE_DEVICE and (within that category) device
private page support need only support rather large setups. On x86, it
requires 64-bit. And on arm64, from what I'm learning after a day or so
of looking around and comparing, I think we must require at least 48 bit
VA support. Otherwise there's just no room for things.
I'm still not sure of how to make room, but working on it.
thanks,
--
John Hubbard
NVIDIA
