Re: [PATCH v2] mm: Fix modifying of page protection by insert_pfn_pmd()
On Thu, Apr 25, 2019 at 05:33:04PM -0700, Dan Williams wrote:
On Thu, Apr 25, 2019 at 12:32 AM Jan Kara <jack(a)suse.cz>
wrote:
> > > We also call vmf_insert_pfn_pmd() in dax_insert_pfn_mkwrite() -- does
> > > that need to change too?
> >
> > It wasn't clear to me that it was a problem. I think that one already
> > happens to be pmd-aligned.
>
> Why would it need to be? The address is taken from vmf->address and that's
> set up in __handle_mm_fault() like .address = address & PAGE_MASK. So I
> don't see anything forcing PMD alignment of the virtual address...
True. So now I'm wondering if the masking should be done internal to
the routine. Given it's prefixed vmf_ it seems to imply the api is
prepared to take raw 'struct vm_fault' parameters. I think I'll go
that route unless someone sees a reason to require the caller to
handle this responsibility.
The vmf_ prefix was originally used to indicate 'returns a vm_fault_t'
instead of 'returns an errno'. That said, I like the interpretation
you're coming up with here, and it makes me wonder if we shouldn't
change vmf_insert_pfn_pmd() to take (vmf, pfn, write) as arguments
instead of separate vma, address & pmd arguments.