Re: [PATCH v4 01/13] mm: pgtable: introduce pte_offset_map_{ro|rw}_nolock()

[David Hildenbrand <david@redhat.com>]

On 24.09.24 08:09, Qi Zheng wrote:
> Currently, the usage of pte_offset_map_nolock() can be divided into the
> following two cases:
> 
> 1) After acquiring PTL, only read-only operations are performed on the PTE
>     page. In this case, the RCU lock in pte_offset_map_nolock() will ensure
>     that the PTE page will not be freed, and there is no need to worry
>     about whether the pmd entry is modified.
> 
> 2) After acquiring PTL, the pte or pmd entries may be modified. At this
>     time, we need to ensure that the pmd entry has not been modified
>     concurrently.
> 
> To more clearing distinguish between these two cases, this commit
> introduces two new helper functions to replace pte_offset_map_nolock().
> For 1), just rename it to pte_offset_map_ro_nolock(). For 2), in addition
> to changing the name to pte_offset_map_rw_nolock(), it also outputs the
> pmdval when successful. It is applicable for may-write cases where any
> modification operations to the page table may happen after the
> corresponding spinlock is held afterwards. But the users should make sure
> the page table is stable like checking pte_same() or checking pmd_same()
> by using the output pmdval before performing the write operations.
> 
> Note: "RO" / "RW" expresses the intended semantics, not that the *kmap*
> will be read-only/read-write protected.
> 
> Subsequent commits will convert pte_offset_map_nolock() into the above
> two functions one by one, and finally completely delete it.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb