From: Ryan Roberts <ryan.roberts@arm.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
SeongJae Park <sj@kernel.org>,
Christoph Hellwig <hch@infradead.org>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Lorenzo Stoakes <lstoakes@gmail.com>,
Uladzislau Rezki <urezki@gmail.com>, Zi Yan <ziy@nvidia.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
damon@lists.linux.dev
Subject: Re: [PATCH v2 4/5] mm: Add new ptep_deref() helper to fully encapsulate pte_t
Date: Wed, 24 May 2023 20:11:38 +0100 [thread overview]
Message-ID: <b818b1f6-f822-477c-6674-6860c84ffdc7@arm.com> (raw)
In-Reply-To: <20230524190618.GR4967@kernel.org>
On 24/05/2023 20:06, Mike Rapoport wrote:
> On Thu, May 18, 2023 at 12:07:26PM +0100, Ryan Roberts wrote:
>> There are many call sites that directly dereference a pte_t pointer.
>> This makes it very difficult to properly encapsulate a page table in the
>> arch code without having to allocate shadow page tables. ptep_deref()
>> aims to solve this by replacing all direct dereferences with a call to
>> this function.
>>
>> The default implementation continues to just dereference the pointer
>> (*ptep), so generated code should be exactly the same. However, it is
>> possible for the architecture to override the default with their own
>> implementation, that can (e.g.) hide certain bits from the core code, or
>> determine young/dirty status by mixing in state from another source.
>>
>> While ptep_get() and ptep_get_lockless() already exist, these are
>> implemented as atomic accesses (e.g. READ_ONCE() in the default case).
>> So rather than using ptep_get() and risking performance regressions,
>> introduce an new variant.
>>
>> Call sites will be converted to use the accessor in future commits.
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> ---
>> include/linux/pgtable.h | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>> index c5a51481bbb9..1161beab2492 100644
>> --- a/include/linux/pgtable.h
>> +++ b/include/linux/pgtable.h
>> @@ -204,6 +204,13 @@ static inline int pudp_set_access_flags(struct vm_area_struct *vma,
>> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>> #endif
>>
>> +#ifndef ptep_deref
>> +static inline pte_t ptep_deref(pte_t *ptep)
>> +{
>> + return *(pte_t *)ptep;
>
> Why do you need the casting here?
I don't - good spot. Will fix for v3.
This is some residue from one of the approaches I took to finding all the call
sites, where I globally did s/pte_t */pte_handle_t/ and typedef'ed pte_handle_t
as a void*. Then the compiler would error on any attempted dereferences, but I
had to explicitly cast in the places that could legitimately dereference.
Thanks for the reviews.
>
>> +}
>> +#endif
>> +
>> #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
>> static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
>> unsigned long address,
>> --
>> 2.25.1
>>
>>
>
next prev parent reply other threads:[~2023-05-24 19:11 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-18 11:07 [PATCH v2 0/5] Encapsulate PTE contents from non-arch code Ryan Roberts
2023-05-18 11:07 ` [PATCH v2 1/5] mm: vmalloc must set pte via arch code Ryan Roberts
2023-05-19 12:09 ` Uladzislau Rezki
2023-05-24 18:47 ` Mike Rapoport
2023-05-18 11:07 ` [PATCH v2 2/5] mm: damon must atomically clear young on ptes and pmds Ryan Roberts
2023-05-18 17:13 ` SeongJae Park
2023-05-19 8:53 ` Ryan Roberts
2023-05-18 23:19 ` Yu Zhao
2023-05-19 9:02 ` Ryan Roberts
2023-05-19 19:54 ` SeongJae Park
2023-05-22 8:53 ` Ryan Roberts
2023-05-24 18:49 ` Mike Rapoport
2023-05-18 11:07 ` [PATCH v2 3/5] mm: Fix failure to unmap pte on highmem systems Ryan Roberts
2023-05-24 18:59 ` Mike Rapoport
2023-05-18 11:07 ` [PATCH v2 4/5] mm: Add new ptep_deref() helper to fully encapsulate pte_t Ryan Roberts
2023-05-18 19:28 ` Yu Zhao
2023-05-19 9:12 ` Ryan Roberts
2023-05-25 9:08 ` Ryan Roberts
2023-05-26 2:02 ` Yu Zhao
2023-05-24 19:06 ` Mike Rapoport
2023-05-24 19:11 ` Ryan Roberts [this message]
2023-05-18 11:07 ` [PATCH v2 5/5] mm: ptep_deref() conversion Ryan Roberts
2023-05-18 12:08 ` Jason Gunthorpe
2023-05-18 17:22 ` SeongJae Park
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