On Tue, Sep 22, 2026 at 04:35:39PM +0100, Lorenzo Stoakes (ARM) wrote:
>Currently, non-x2 sh specifies CONFIG_MMU_GATHER_RCU_TABLE_FREE allowing
>RCU page table freeing.
>
>sh-X2 is problematic because it utilises slab-allocated PMD page tables,
>and thus tlb_remove_ptdesc() cannot be used in these cases.
>
>All other sh variants are fine as commit e3ecf7c7d082 ("mm: pgtable:
>convert some architectures to use tlb_remove_ptdesc()") already converted
>page table freeing to use tlb_remove_ptdesc(), which does so after an RCU
>grace period when CONFIG_MMU_GATHER_RCU_TABLE_FREE is specified.
>
>Resolve this issue by firstly specifying CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE
>for sh-X2, so the arch can provide its own __tlb_remove_table()
>implementation (called after the RCU grace period).
>
>Then, convert __pmd_free_tlb() to tag the pointer to the PMD, and have
>__tlb_remove_table() check this tag to determine whether to free via the
>slab or to use pagetable_dtor_free().
Makes sense to me, so RCU callback won't mistake a slab PMD for a PTE
page :)
>This follows the pattern used by sparc64 as implemented in commit
>4a0100f7546f ("sparc64: use RCU page table freeing").
>
>Previously __pmd_free_tlb() freed PMD page tables immediately, before any
>TLB flush IPI. This seems to be a pre-existing bug, which this change also
>resolves.
>
>CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE is only specified for sh-X2, as setting
>it disables CONFIG_PT_RECLAIM and causes __tlb_remove_table_one() to call
>tlb_remove_table_sync_rcu() and synchronize_rcu() in turn, and this is not
>necessary for other sh variants.
>
>This forms part of an overall effort to switch every architecture to this
>mode.
>
>Acked-by: Kiryl Shutsemau (Meta) <[email protected]>
>Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
>---
LGTM, feel free to add:
Acked-by: Lance Yang <[email protected]>
