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Howlett" , Vlastimil Babka , Shakeel Butt , David Hildenbrand , Mike Rapoport , Michal Hocko , Uladzislau Rezki , Toshi Kani , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Catalin Marinas , Will Deacon , Dev Jain , Ryan Roberts , David Carlier , linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org, syzbot+fd95a72470f5a44e464c@syzkaller.appspotmail.com Subject: Re: [PATCH mm-hotfixes v2 0/4] mm: fix UAF caused by race between ptdump and vmap pgtable freeing Message-ID: References: <20260712-series-vmap-race-fix-v2-0-ad134cc3a12a@kernel.org> <178404602957.85099.8935151447302412515.b4-reply@b4> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <178404602957.85099.8935151447302412515.b4-reply@b4> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1BAE4120005 X-Stat-Signature: qbzkm76cxrx8xm1ec9zdu4ffya5qrw6y X-HE-Tag: 1784048710-182989 X-HE-Meta: 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 NsiqUlAD sRc6XIGP4T30XRm0d2Tw6oSPP4+TJ8HWkNKVj2f2mNUKsqqdrCc2c6lKdtbEKGAqh2Y9hNNV09TjHKtrZkoeFGPbWf81gl5v+jOXT7l3tn48CPGc4odVz7NIRO7zDMu/48aZdU/Lj569/CbKN7Y0Ug0VQIoxL6yhd7r8TEVHbIIpUsGbZFlvtPgwN7m+ClNrPc6jX9HYXMJVjBgl9nxZyU6foXv/X7EjtIZ5DO88m0qHnKvtcaqN4rI2SzXHErhAwHiqBWWNS0WHzhMS/+cPYp9aihA11dV0u0VUfR59vWr8orQkprJtLnr0CrgMnRF/Ap0uMTC16yv4s2sm2+oFuDvPupoWG5gPg5SjKyNytgItwUzZlDb1VcDwR82lwuAeAAGU13vFn2rYx9u/moi7+EfGNaiIC8lBciOP8 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 14, 2026 at 05:20:29PM +0100, Lorenzo Stoakes (ARM) wrote: > Basically you need the IRQs disabled to get the semi-RCU behaviour and to > be able to safely traverse page tables that way. > > So with CONFIG_PT_RECLAIM you're safe to RCU traverse PTEs only. I think this is stale. Since 1fb3d8c20bfa ("mm/mmu_gather: replace IPI with synchronize_rcu() when batch allocation fails") the !PT_RECLAIM fallback is a real grace period -- note your own quote of __tlb_remove_table_one() calls tlb_remove_table_sync_rcu(), which is synchronize_rcu() nowadays, not the IPI broadcast. The name invites the confusion. Together with a37259732a7d ("x86/mm: Make MMU_GATHER_RCU_TABLE_FREE unconditional") that means every freeing path through the generic mmu_gather is genuine RCU, batched or not, all levels. A plain rcu_read_lock() walker is protected; IRQs disabled is not required. > HAVE_ARCH_TLB_REMOVE_TABLE is set for powerpc, which also enables PTDUMP :) > and that's because it actually tracks multiple PTE page tables together as > a fragment. sparc also sets it with SMP. So the audit list for custom tlb_remove_table() implementations is powerpc and sparc -- everything else gets the generic behaviour above. No disagreement on the rest: the walker needs ptep_get_lockless()/pmdp_get_lockless(), and the ppc kernel-side fragments need a look. -- Kiryl Shutsemau / Kirill A. Shutemov