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X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org 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) >Signed-off-by: Lorenzo Stoakes (ARM) >--- LGTM, feel free to add: Acked-by: Lance Yang _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv