linux-kernel - Re: [PATCH hotfix 6.12 v4 4/5] mm: refactor arch_calc_vm_flag

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Message-ID: <3f184fad-e0da-470a-888e-70a17419e206@lucifer.local>
Date: Wed, 30 Oct 2024 11:53:06 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Jann Horn <jannh@...gle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>, Will Deacon <will@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Andreas Larsson <andreas@...sler.com>,
        "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, Yang Shi <yang@...amperecomputing.com>
Subject: Re: [PATCH hotfix 6.12 v4 4/5] mm: refactor arch_calc_vm_flag_bits()
 and arm64 MTE handling

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-.

>
> > 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.

>
> >
> >> >  	 */
> >> > -	if (system_supports_mte() && (flags & MAP_ANONYMOUS))
> >> > +	if (system_supports_mte() &&
> >> > +	    ((flags & MAP_ANONYMOUS) || shmem_file(file)))
> >> >  		return VM_MTE_ALLOWED;
> >> >
> >> >  	return 0;
> >> >  }
> >
> > This will conflict with the arm64 for-next/core tree as it's adding
> > a MAP_HUGETLB check. Trivial resolution though, Stephen will handle it.

Thanks!

> >
>