Re: [PATCH hotfix 6.12 v4 4/5] mm: refactor arch_calc_vm_flag_bits() and arm64 MTE handling

[Yang Shi]

On 10/30/24 5:39 AM, Catalin Marinas wrote:
> On Wed, Oct 30, 2024 at 11:53:06AM +0000, Lorenzo Stoakes wrote:
> > On Wed, Oct 30, 2024 at 12:09:43PM +0100, Vlastimil Babka wrote:
> > > On 10/30/24 11:58, Catalin Marinas wrote:
> > > > On Wed, Oct 30, 2024 at 10:18:27AM +0100, Vlastimil Babka wrote:
> > > > > On 10/29/24 19:11, Lorenzo Stoakes wrote:
> > > > > > --- a/arch/arm64/include/asm/mman.h
> > > > > > +++ b/arch/arm64/include/asm/mman.h
> > > > > > @@ -6,6 +6,8 @@
> > > > > >
> > > > > >   #ifndef BUILD_VDSO
> > > > > >   #include <linux/compiler.h>
> > > > > > +#include <linux/fs.h>
> > > > > > +#include <linux/shmem_fs.h>
> > > > > >   #include <linux/types.h>
> > > > > >
> > > > > >   static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
> > > > > > @@ -31,19 +33,21 @@ static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
> > > > > >   }
> > > > > >   #define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
> > > > > >
> > > > > > -static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
> > > > > > +static inline unsigned long arch_calc_vm_flag_bits(struct file *file,
> > > > > > +						   unsigned long flags)
> > > > > >   {
> > > > > >   	/*
> > > > > >   	 * Only allow MTE on anonymous mappings as these are guaranteed to be
> > > > > >   	 * backed by tags-capable memory. The vm_flags may be overridden by a
> > > > > >   	 * filesystem supporting MTE (RAM-based).
> > > > > We should also eventually remove the last sentence or even replace it with
> > > > > its negation, or somebody might try reintroducing the pattern that won't
> > > > > work anymore (wasn't there such a hugetlbfs thing in -next?).
> > > > I agree, we should update this comment as well though as a fix this
> > > > patch is fine for now.
> > > >
> > > > There is indeed a hugetlbfs change in -next adding VM_MTE_ALLOWED. It
> > > > should still work after the above change but we'd need to move it over
> > > I guess it will work after the above change, but not after 5/5?
> > >
> > > > here (and fix the comment at the same time). We'll probably do it around
> > > > -rc1 or maybe earlier once this fix hits mainline.
> > > I assume this will hopefully go to rc7.
> > To be clear - this is a CRITICAL fix that MUST land for 6.12. I'd be inclined to
> > try to get it to an earlier rc-.
> Ah, good point. So after this series is merged at rc6/rc7, the new
> MTE+hugetlbfs in -next won't work. Not an issue, it can be sorted out
> later.
>
> > > > I don't think we have
> > > > an equivalent of shmem_file() for hugetlbfs, we'll need to figure
> > > > something out.
> > > I've found is_file_hugepages(), could work? And while adding the hugetlbfs
> > > change here, the comment could be adjusted too, right?
> > Right but the MAP_HUGETLB should work to? Can we save such changes that
> > alter any kind of existing behaviour to later series?
> >
> > As this is going to be backported (by me...!) and I don't want to risk
> > inadvertant changes.
> MAP_HUGETLB and is_file_hugepages() fixes can go in after 6.13-rc1. This
> series is fine as is, we wouldn't backport any MAP_HUGETLB changes
> anyway since the flag check wasn't the only issue that needed addressing
> for hugetlb MTE mappings.

I agree. The fix looks trivial.

>