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

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Message-ID: <c8760d0e-acbd-4fd6-b077-58b5c374cad3@suse.cz>
Date: Wed, 30 Oct 2024 12:09:43 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.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 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.

> 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?

> 
>> >  	 */
>> > -	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.
>