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

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Message-ID: <d8ae6912-66f3-4910-bc61-cd653d8dbf36@os.amperecomputing.com>
Date: Wed, 30 Oct 2024 08:00:36 -0700
From: Yang Shi <yang@...amperecomputing.com>
To: Catalin Marinas <catalin.marinas@....com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
 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>
Subject: Re: [PATCH hotfix 6.12 v4 4/5] mm: refactor arch_calc_vm_flag_bits()
 and arm64 MTE handling



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.

>