Re: [PATCH RFC 2/2] mm/x86/pat: Do proper PAT bit shift for large mappings

[Peter Xu]

On Thu, May 23, 2024 at 07:07:06PM -0400, Peter Xu wrote:
> On Thu, May 23, 2024 at 03:48:22PM -0700, Dave Hansen wrote:
> > On 5/23/24 15:37, Peter Xu wrote:
> > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > > index 317de2afd371..c4a2356b1a54 100644
> > > --- a/mm/huge_memory.c
> > > +++ b/mm/huge_memory.c
> > > @@ -1135,7 +1135,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> > >  		goto out_unlock;
> > >  	}
> > >  
> > > -	entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
> > > +	entry = pmd_mkhuge(pfn_t_pmd(pfn, pgprot_4k_2_large(prot)));
> > >  	if (pfn_t_devmap(pfn))
> > >  		entry = pmd_mkdevmap(entry);
> > >  	if (write) {
> > 
> > Does this even compile on non-x86 architectures?
> 
> Probably not..  I think I can define a pgprot_to_large() globally, pointing
> that to pgprot_4k_2_large() on x86 and make the fallback to be noop.  And
> if there's a new version I'll guarantee to run over my cross compilers.
> 
> Any comments on the idea itself?  Do we have a problem, or maybe I
> overlooked something?

I also attached one new version of patch 2 that should pass the cross
builds.  Please reviewers feel free to look at this one instead.  From x86
perspective they should be the same thing.

Thanks,

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