Re: [PATCH v3 13/13] mm/huge_memory: add and use has_deposited_pgtable()

[Yin Tirui]

On 4/14/26 17:44, David Hildenbrand (Arm) wrote:
> 
> I mean, we need some indication to know also during folio splitting
> whether we can just discard the PMD, as we can refault it later, or
> whether we really have to install a PTE table.
> 
> What if someone used remap_pfn_range() on some part of the VMA, and
> faults on another part?
> 
> Doesn't really work.
> 
> Do we have users of remap_pfn_range() that have ->fault set? If not, we
> should probably just disallow this combination.

I did a quick tree-wide grep:
$ git grep -l "remap_pfn_range" | xargs grep -l "\.fault\s*="
arch/powerpc/platforms/book3s/vas-api.c
drivers/infiniband/hw/hfi1/file_ops.c
drivers/uio/uio.c
drivers/vfio/pci/vfio_pci_core.c
fs/proc/vmcore.c
security/selinux/selinuxfs.c

It turns out there are two users of this "hybrid" approach in the kernel:
1. fs/proc/vmcore.c: It pre-maps via remap_pfn_range() but registers
mmap_vmcore_fault().
2. arch/powerpc/platforms/book3s/vas-api.c: It pre-maps via
remap_pfn_range(), but registers vas_mmap_fault().

> 
> Then we know for sure whether something was installed through
> remap_pfn_range() or through a fault handler.
> 

How would you suggest we proceed here?

-- 
Yin Tirui