Re: [v2 PATCH 1/2] hugetlb: arm64: add mte support

David Hildenbrand
2024-09-04T18:35:37Z

On 04.09.24 19:57, Yang Shi wrote:
>
>
> On 9/3/24 2:35 PM, David Hildenbrand wrote:
>> On 03.09.24 18:46, Yang Shi wrote:
>>>
>>>
>>> On 9/2/24 7:33 AM, David Hildenbrand wrote:
>>>> On 21.08.24 20:47, Yang Shi wrote:
>>>>> Enable MTE support for hugetlb.
>>>>>
>>>>> The MTE page flags will be set on the head page only.  When copying
>>>>> hugetlb folio, the tags for all tail pages will be copied when copying
>>>>> head page.
>>>>>
>>>>> When freeing hugetlb folio, the MTE flags will be cleared.
>>>>>
>>>>> Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
>>>>> ---
>>>>>    arch/arm64/include/asm/hugetlb.h | 11 ++++++++++-
>>>>>    arch/arm64/include/asm/mman.h    |  3 ++-
>>>>>    arch/arm64/kernel/hibernate.c    |  7 +++++++
>>>>>    arch/arm64/kernel/mte.c          | 25 +++++++++++++++++++++++--
>>>>>    arch/arm64/kvm/guest.c           | 16 +++++++++++++---
>>>>>    arch/arm64/kvm/mmu.c             | 11 +++++++++++
>>>>>    arch/arm64/mm/copypage.c         | 25 +++++++++++++++++++++++--
>>>>>    fs/hugetlbfs/inode.c             |  2 +-
>>>>>    8 files changed, 90 insertions(+), 10 deletions(-)
>>>>>
>>>>> v2: * Reimplemented the patch to fix the comments from Catalin.
>>>>>       * Added test cases (patch #2) per Catalin.
>>>>>
>>>>> diff --git a/arch/arm64/include/asm/hugetlb.h
>>>>> b/arch/arm64/include/asm/hugetlb.h
>>>>> index 293f880865e8..00a1f75d40ee 100644
>>>>> --- a/arch/arm64/include/asm/hugetlb.h
>>>>> +++ b/arch/arm64/include/asm/hugetlb.h
>>>>> @@ -11,6 +11,7 @@
>>>>>    #define __ASM_HUGETLB_H
>>>>>      #include <asm/cacheflush.h>
>>>>> +#include <asm/mte.h>
>>>>>    #include <asm/page.h>
>>>>>      #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
>>>>> @@ -20,7 +21,15 @@ extern bool
>>>>> arch_hugetlb_migration_supported(struct hstate *h);
>>>>>      static inline void arch_clear_hugetlb_flags(struct folio *folio)
>>>>>    {
>>>>> -    clear_bit(PG_dcache_clean, &folio->flags);
>>>>> +    const unsigned long clear_flags = BIT(PG_dcache_clean) |
>>>>> +        BIT(PG_mte_tagged) | BIT(PG_mte_lock);
>>>>> +
>>>>> +    if (!system_supports_mte()) {
>>>>> +        clear_bit(PG_dcache_clean, &folio->flags);
>>>>> +        return;
>>>>> +    }
>>>>> +
>>>>> +    folio->flags &= ~clear_flags;
>>>>>    }
>>>>>    #define arch_clear_hugetlb_flags arch_clear_hugetlb_flags
>>>>>    diff --git a/arch/arm64/include/asm/mman.h
>>>>> b/arch/arm64/include/asm/mman.h
>>>>> index 5966ee4a6154..304dfc499e68 100644
>>>>> --- a/arch/arm64/include/asm/mman.h
>>>>> +++ b/arch/arm64/include/asm/mman.h
>>>>> @@ -28,7 +28,8 @@ static inline unsigned long
>>>>> arch_calc_vm_flag_bits(unsigned long flags)
>>>>>         * backed by tags-capable memory. The vm_flags may be
>>>>> overridden by a
>>>>>         * filesystem supporting MTE (RAM-based).
>>>>>         */
>>>>> -    if (system_supports_mte() && (flags & MAP_ANONYMOUS))
>>>>> +    if (system_supports_mte() &&
>>>>> +        (flags & (MAP_ANONYMOUS | MAP_HUGETLB)))
>>>>>            return VM_MTE_ALLOWED;
>>>>>          return 0;
>>>>> diff --git a/arch/arm64/kernel/hibernate.c
>>>>> b/arch/arm64/kernel/hibernate.c
>>>>> index 02870beb271e..722e76f29141 100644
>>>>> --- a/arch/arm64/kernel/hibernate.c
>>>>> +++ b/arch/arm64/kernel/hibernate.c
>>>>> @@ -266,10 +266,17 @@ static int swsusp_mte_save_tags(void)
>>>>>            max_zone_pfn = zone_end_pfn(zone);
>>>>>            for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn;
>>>>> pfn++) {
>>>>>                struct page *page = pfn_to_online_page(pfn);
>>>>> +            struct folio *folio;
>>>>>                  if (!page)
>>>>>                    continue;
>>>>>    +            folio = page_folio(page);
>>>>> +
>>>>> +            if (folio_test_hugetlb(folio) &&
>>>>> +                !page_mte_tagged(&folio->page))
>>>>> +                continue;
>>>>
>>>> Can we have folio_test_mte_tagged() whereby you make sure that only
>>>> folio_test_hugetlb() uses it for now (VM_WARN_ON_ONCE) and then make
>>>> sure that nobody uses page_mte_tagged() on hugetlb folios
>>>> (VM_WARN_ON_ONCE)?
>>>
>>>
>>> IIUC, you mean something like the below?
>>>
>>> bool folio_test_mte_tagged(struct folio *folio)
>>> {
>>>       VM_WARN_ON_ONCE(!folio_test_hugetlb(folio));
>>>
>>>       return test_bit(PG_mte_tagged, &folio->page->flags);
>>
>> folio->flags
>>
>>> }
>>>
>>> bool page_mte_tagged(struct page *page)
>>> {
>>>       struct folio *folio = page_folio(page);
>>>
>>>       VM_WARN_ON_ONCE(folio_test_hugetlb(folio));
>>
>> Yes, but better as
>>
>> VM_WARN_ON_ONCE(folio_test_hugetlb(page_folio(page)));
>
> I see. But I think all the call sites for folio_test_mte_tagged()
> actually need have folio_test_hugetlb() before it. So the warn seems not
> very useful other than warning on some misuse.

... well, that's the whole reason for them :)

>
>>
>>>
>>>       return test_bit(PG_mte_tagged, &pge->flags);
>>> }
>>>
>>>>
>>>> Same for folio_set_mte_tagged() and other functions. We could slap a
>>>> "hugetlb" into the function names, but maybe in the future we'll be
>>>> able to use a single flag per folio (I know, it's complicated ...).
>>>
>>> A single flag per folio should be the future direction, but I haven't
>>> done the research so can't tell how complicated it will be.
>>
>> There were some discussions on it, and it's tricky. So maybe we should
>> really just have folio_test_hugetlb_mte_tagged() etc. for now
>
> Either w/ hugetlb or w/o hugetlb is fine, I don't have strong opinion on
> the naming.

Let's go with "hugetlb" for now, using it for other large folios is out
of sight a bit ... at least right now :)

--
Cheers,

David / dhildenb