Re: [PATCH Part2 v6 09/49] x86/fault: Add support to handle the RMP fault for user address

Jarkko Sakkinen
2022-09-06T10:33:59Z

On Tue, Sep 06, 2022 at 01:25:10PM +0300, Jarkko Sakkinen wrote:
> On Tue, Aug 09, 2022 at 06:55:43PM +0200, Borislav Petkov wrote:
> > On Mon, Jun 20, 2022 at 11:03:43PM +0000, Ashish Kalra wrote:
> > > + pfn = pte_pfn(*pte);
> > > +
> > > + /* If its large page then calculte the fault pfn */
> > > + if (level > PG_LEVEL_4K) {
> > > + unsigned long mask;
> > > +
> > > + mask = pages_per_hpage(level) - pages_per_hpage(level - 1);
> > > + pfn |= (address >> PAGE_SHIFT) & mask;
> >
> > Oh boy, this is unnecessarily complicated. Isn't this
> >
> > pfn |= pud_index(address);
> >
> > or
> > pfn |= pmd_index(address);
>
> I played with this a bit and ended up with
>
> pfn = pte_pfn(*pte) | PFN_DOWN(address & page_level_mask(level - 1));
>
> Unless I got something terribly wrong, this should do the
> same (see the attached patch) as the existing calculations.

IMHO a better name for this function would be do_user_rmp_addr_fault() as
it is more consistent with the existing function names.

BR, Jarkko