VM_UFFD_MISSING flag is mutually exclussive with VM_MAYOVERLAY flag as they
both use the same bit position i.e 0x00000200 in the vm_flags. Let's update
show_smap_vma_flags() to display the correct flags depending on CONFIG_MMU.
Cc: Andrew Morton <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Anshuman Khandual <[email protected]>
---
This applies on v6.8-rc3
fs/proc/task_mmu.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 3f78ebbb795f..1c4eb25cfc17 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -681,7 +681,11 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
[ilog2(VM_HUGEPAGE)] = "hg",
[ilog2(VM_NOHUGEPAGE)] = "nh",
[ilog2(VM_MERGEABLE)] = "mg",
+#ifdef CONFIG_MMU
[ilog2(VM_UFFD_MISSING)]= "um",
+#else
+ [ilog2(VM_MAYOVERLAY)] = "ov",
+#endif /* CONFIG_MMU */
[ilog2(VM_UFFD_WP)] = "uw",
#ifdef CONFIG_ARM64_MTE
[ilog2(VM_MTE)] = "mt",
--
2.25.1
On 08.02.24 09:48, Anshuman Khandual wrote:
> VM_UFFD_MISSING flag is mutually exclussive with VM_MAYOVERLAY flag as they
> both use the same bit position i.e 0x00000200 in the vm_flags. Let's update
> show_smap_vma_flags() to display the correct flags depending on CONFIG_MMU.
>
> Cc: Andrew Morton <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Anshuman Khandual <[email protected]>
> ---
> This applies on v6.8-rc3
>
> fs/proc/task_mmu.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 3f78ebbb795f..1c4eb25cfc17 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -681,7 +681,11 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
> [ilog2(VM_HUGEPAGE)] = "hg",
> [ilog2(VM_NOHUGEPAGE)] = "nh",
> [ilog2(VM_MERGEABLE)] = "mg",
> +#ifdef CONFIG_MMU
> [ilog2(VM_UFFD_MISSING)]= "um",
> +#else
> + [ilog2(VM_MAYOVERLAY)] = "ov",
> +#endif /* CONFIG_MMU */
> [ilog2(VM_UFFD_WP)] = "uw",
> #ifdef CONFIG_ARM64_MTE
> [ilog2(VM_MTE)] = "mt",
Reviewed-by: David Hildenbrand <[email protected]>
--
Cheers,
David / dhildenb
On Thu, 8 Feb 2024 17:48:26 +0100 David Hildenbrand <[email protected]> wrote:
> On 08.02.24 09:48, Anshuman Khandual wrote:
> > VM_UFFD_MISSING flag is mutually exclussive with VM_MAYOVERLAY flag as they
> > both use the same bit position i.e 0x00000200 in the vm_flags. Let's update
> > show_smap_vma_flags() to display the correct flags depending on CONFIG_MMU.
> >
> > Cc: Andrew Morton <[email protected]>
> > Cc: David Hildenbrand <[email protected]>
> > Cc: [email protected]
> > Cc: [email protected]
> > Signed-off-by: Anshuman Khandual <[email protected]>
> > ---
> > This applies on v6.8-rc3
> >
> > fs/proc/task_mmu.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 3f78ebbb795f..1c4eb25cfc17 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -681,7 +681,11 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
> > [ilog2(VM_HUGEPAGE)] = "hg",
> > [ilog2(VM_NOHUGEPAGE)] = "nh",
> > [ilog2(VM_MERGEABLE)] = "mg",
> > +#ifdef CONFIG_MMU
> > [ilog2(VM_UFFD_MISSING)]= "um",
> > +#else
> > + [ilog2(VM_MAYOVERLAY)] = "ov",
> > +#endif /* CONFIG_MMU */
> > [ilog2(VM_UFFD_WP)] = "uw",
> > #ifdef CONFIG_ARM64_MTE
> > [ilog2(VM_MTE)] = "mt",
>
> Reviewed-by: David Hildenbrand <[email protected]>
I'm thinking
Fixes: b6b7a8faf05c ("mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings")
Cc: <[email protected]>
On 08.02.24 21:40, Andrew Morton wrote:
> On Thu, 8 Feb 2024 17:48:26 +0100 David Hildenbrand <[email protected]> wrote:
>
>> On 08.02.24 09:48, Anshuman Khandual wrote:
>>> VM_UFFD_MISSING flag is mutually exclussive with VM_MAYOVERLAY flag as they
>>> both use the same bit position i.e 0x00000200 in the vm_flags. Let's update
>>> show_smap_vma_flags() to display the correct flags depending on CONFIG_MMU.
>>>
>>> Cc: Andrew Morton <[email protected]>
>>> Cc: David Hildenbrand <[email protected]>
>>> Cc: [email protected]
>>> Cc: [email protected]
>>> Signed-off-by: Anshuman Khandual <[email protected]>
>>> ---
>>> This applies on v6.8-rc3
>>>
>>> fs/proc/task_mmu.c | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>> index 3f78ebbb795f..1c4eb25cfc17 100644
>>> --- a/fs/proc/task_mmu.c
>>> +++ b/fs/proc/task_mmu.c
>>> @@ -681,7 +681,11 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>>> [ilog2(VM_HUGEPAGE)] = "hg",
>>> [ilog2(VM_NOHUGEPAGE)] = "nh",
>>> [ilog2(VM_MERGEABLE)] = "mg",
>>> +#ifdef CONFIG_MMU
>>> [ilog2(VM_UFFD_MISSING)]= "um",
>>> +#else
>>> + [ilog2(VM_MAYOVERLAY)] = "ov",
>>> +#endif /* CONFIG_MMU */
>>> [ilog2(VM_UFFD_WP)] = "uw",
>>> #ifdef CONFIG_ARM64_MTE
>>> [ilog2(VM_MTE)] = "mt",
>>
>> Reviewed-by: David Hildenbrand <[email protected]>
>
> I'm thinking
>
> Fixes: b6b7a8faf05c ("mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings")
> Cc: <[email protected]>
I'm having a hard time believing that anybody that runs a !MMU kernel
would actually care about this bit being exposed as "ov" instead of "uw".
So in my thinking, one could even update
Documentation/filesystems/proc.rst to just mention that "uw" on !MMU is
only used for internal purposes.
But now, I actually read what that structure says:
"Don't forget to update Documentation/ on changes."
So, let's look there: Documentation/filesystems/proc.rst
"Note that there is no guarantee that every flag and associated mnemonic
will be present in all further kernel releases. Things get changed, the
flags may be vanished or the reverse -- new added. Interpretation of
their meaning might change in future as well. So each consumer of these
flags has to follow each specific kernel version for the exact semantic.
This file is only present if the CONFIG_MMU kernel configuration option
is enabled."
And in fact
$ git grep MMU fs/proc/Makefile
fs/proc/Makefile:proc-$(CONFIG_MMU) := task_mmu.o
So I rewoke my RB, this patch should be dropped and was never even
tested unless I am missing something important.
--
Cheers,
David / dhildenb
On 2/10/24 04:01, David Hildenbrand wrote:
> On 08.02.24 21:40, Andrew Morton wrote:
>> On Thu, 8 Feb 2024 17:48:26 +0100 David Hildenbrand <[email protected]> wrote:
>>
>>> On 08.02.24 09:48, Anshuman Khandual wrote:
>>>> VM_UFFD_MISSING flag is mutually exclussive with VM_MAYOVERLAY flag as they
>>>> both use the same bit position i.e 0x00000200 in the vm_flags. Let's update
>>>> show_smap_vma_flags() to display the correct flags depending on CONFIG_MMU.
>>>>
>>>> Cc: Andrew Morton <[email protected]>
>>>> Cc: David Hildenbrand <[email protected]>
>>>> Cc: [email protected]
>>>> Cc: [email protected]
>>>> Signed-off-by: Anshuman Khandual <[email protected]>
>>>> ---
>>>> This applies on v6.8-rc3
>>>>
>>>> fs/proc/task_mmu.c | 4 ++++
>>>> 1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>>> index 3f78ebbb795f..1c4eb25cfc17 100644
>>>> --- a/fs/proc/task_mmu.c
>>>> +++ b/fs/proc/task_mmu.c
>>>> @@ -681,7 +681,11 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>>>> [ilog2(VM_HUGEPAGE)] = "hg",
>>>> [ilog2(VM_NOHUGEPAGE)] = "nh",
>>>> [ilog2(VM_MERGEABLE)] = "mg",
>>>> +#ifdef CONFIG_MMU
>>>> [ilog2(VM_UFFD_MISSING)]= "um",
>>>> +#else
>>>> + [ilog2(VM_MAYOVERLAY)] = "ov",
>>>> +#endif /* CONFIG_MMU */
>>>> [ilog2(VM_UFFD_WP)] = "uw",
>>>> #ifdef CONFIG_ARM64_MTE
>>>> [ilog2(VM_MTE)] = "mt",
>>>
>>> Reviewed-by: David Hildenbrand <[email protected]>
>>
>> I'm thinking
>>
>> Fixes: b6b7a8faf05c ("mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings")
>> Cc: <[email protected]>
>
> I'm having a hard time believing that anybody that runs a !MMU kernel would actually care about this bit being exposed as "ov" instead of "uw".
>
> So in my thinking, one could even update Documentation/filesystems/proc.rst to just mention that "uw" on !MMU is only used for internal purposes.
>
> But now, I actually read what that structure says:
>
> "Don't forget to update Documentation/ on changes."
>
> So, let's look there: Documentation/filesystems/proc.rst
>
> "Note that there is no guarantee that every flag and associated mnemonic will be present in all further kernel releases. Things get changed, the flags may be vanished or the reverse -- new added. Interpretation of their meaning might change in future as well. So each consumer of these flags has to follow each specific kernel version for the exact semantic.
>
> This file is only present if the CONFIG_MMU kernel configuration option is enabled."
>
> And in fact
>
> $ git grep MMU fs/proc/Makefile
> fs/proc/Makefile:proc-$(CONFIG_MMU) := task_mmu.o
Ahh! you are right, completely missed that.
>
>
> So I rewoke my RB, this patch should be dropped and was never even tested unless I am missing something important.
Fair enough, let's drop this patch. I found this via code inspection while
looking into VM_UFFD_MISSING definition, booted with default configs which
has CONFIG_MMU enabled. But this was an oversight, my bad.
On 12.02.24 03:00, Anshuman Khandual wrote:
>
> On 2/10/24 04:01, David Hildenbrand wrote:
>> On 08.02.24 21:40, Andrew Morton wrote:
>>> On Thu, 8 Feb 2024 17:48:26 +0100 David Hildenbrand <[email protected]> wrote:
>>>
>>>> On 08.02.24 09:48, Anshuman Khandual wrote:
>>>>> VM_UFFD_MISSING flag is mutually exclussive with VM_MAYOVERLAY flag as they
>>>>> both use the same bit position i.e 0x00000200 in the vm_flags. Let's update
>>>>> show_smap_vma_flags() to display the correct flags depending on CONFIG_MMU.
>>>>>
>>>>> Cc: Andrew Morton <[email protected]>
>>>>> Cc: David Hildenbrand <[email protected]>
>>>>> Cc: [email protected]
>>>>> Cc: [email protected]
>>>>> Signed-off-by: Anshuman Khandual <[email protected]>
>>>>> ---
>>>>> This applies on v6.8-rc3
>>>>>
>>>>> fs/proc/task_mmu.c | 4 ++++
>>>>> 1 file changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>>>> index 3f78ebbb795f..1c4eb25cfc17 100644
>>>>> --- a/fs/proc/task_mmu.c
>>>>> +++ b/fs/proc/task_mmu.c
>>>>> @@ -681,7 +681,11 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>>>>> [ilog2(VM_HUGEPAGE)] = "hg",
>>>>> [ilog2(VM_NOHUGEPAGE)] = "nh",
>>>>> [ilog2(VM_MERGEABLE)] = "mg",
>>>>> +#ifdef CONFIG_MMU
>>>>> [ilog2(VM_UFFD_MISSING)]= "um",
>>>>> +#else
>>>>> + [ilog2(VM_MAYOVERLAY)] = "ov",
>>>>> +#endif /* CONFIG_MMU */
>>>>> [ilog2(VM_UFFD_WP)] = "uw",
>>>>> #ifdef CONFIG_ARM64_MTE
>>>>> [ilog2(VM_MTE)] = "mt",
>>>>
>>>> Reviewed-by: David Hildenbrand <[email protected]>
>>>
>>> I'm thinking
>>>
>>> Fixes: b6b7a8faf05c ("mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings")
>>> Cc: <[email protected]>
>>
>> I'm having a hard time believing that anybody that runs a !MMU kernel would actually care about this bit being exposed as "ov" instead of "uw".
>>
>> So in my thinking, one could even update Documentation/filesystems/proc.rst to just mention that "uw" on !MMU is only used for internal purposes.
>>
>> But now, I actually read what that structure says:
>>
>> "Don't forget to update Documentation/ on changes."
>>
>> So, let's look there: Documentation/filesystems/proc.rst
>>
>> "Note that there is no guarantee that every flag and associated mnemonic will be present in all further kernel releases. Things get changed, the flags may be vanished or the reverse -- new added. Interpretation of their meaning might change in future as well. So each consumer of these flags has to follow each specific kernel version for the exact semantic.
>>
>> This file is only present if the CONFIG_MMU kernel configuration option is enabled."
>>
>> And in fact
>>
>> $ git grep MMU fs/proc/Makefile
>> fs/proc/Makefile:proc-$(CONFIG_MMU) := task_mmu.o
>
> Ahh! you are right, completely missed that.
>
>>
>>
>> So I rewoke my RB, this patch should be dropped and was never even tested unless I am missing something important.
>
> Fair enough, let's drop this patch. I found this via code inspection while
> looking into VM_UFFD_MISSING definition, booted with default configs which
> has CONFIG_MMU enabled. But this was an oversight, my bad.
>
No worries, NUMMU is just absolutely weird :)
--
Cheers,
David / dhildenb