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Thu, 5 Jun 2025 04:34:29 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id ViaJBVUeQWirdwAAD6G6ig (envelope-from ); Thu, 05 Jun 2025 04:34:29 +0000 Date: Thu, 5 Jun 2025 06:34:23 +0200 From: Oscar Salvador To: Lorenzo Stoakes Cc: Andrew Morton , Barry Song , David Hildenbrand , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Muchun Song , Huacai Chen , WANG Xuerui , Jonas Bonn , Stefan Kristiansson , Stafford Horne , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Jann Horn , loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, linux-openrisc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH v2] mm/pagewalk: split walk_page_range_novma() into kernel/user parts Message-ID: References: <20250604141958.111300-1-lorenzo.stoakes@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250604141958.111300-1-lorenzo.stoakes@oracle.com> X-Stat-Signature: ibj31py4d44rmwxa3ycg8uj1hdg1rw7a X-Rspamd-Queue-Id: 5F38E40006 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1749098072-989022 X-HE-Meta: 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 TnCYLQfV Bbr4cuLmLqeXmGxQMtLBAx7X1ZIhh4BXFs8pH9Kc8mwpvdEGVNnnDLQgaIeNzWA/VWBt97YbgJLm+vgJKmmHebYWM3W/i8gA4qhi2gTaY9ZIkqabVsKz4JSX8ms4vbGYmVakvlls4HfjVQWebG1DuCqRWrrknfU0is3rAx5APAHGrZXn/l8QRI+wKJo3yr6D8mbmDwVt/onJuXFitmb0IXJHBhoqdEaB4xCRGSn4/NxSN80Y0ZMT+XZBTXSX026kw5xZoBdtF0XA367EjMFYtssDiGq2gJnGO9Oadyv3lkli66ToUtBm8ENMnwEpEc/hoNQQT6vANPxdm0L5Lq8Cdz4BRsCD1WuekZMLsTUob8rxSC8w= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jun 04, 2025 at 03:19:58PM +0100, Lorenzo Stoakes wrote: > The walk_page_range_novma() function is rather confusing - it supports two > modes, one used often, the other used only for debugging. > > The first mode is the common case of traversal of kernel page tables, which > is what nearly all callers use this for. > > Secondly it provides an unusual debugging interface that allows for the > traversal of page tables in a userland range of memory even for that memory > which is not described by a VMA. > > It is far from certain that such page tables should even exist, but perhaps > this is precisely why it is useful as a debugging mechanism. > > As a result, this is utilised by ptdump only. Historically, things were > reversed - ptdump was the only user, and other parts of the kernel evolved > to use the kernel page table walking here. > > Since we have some complicated and confusing locking rules for the novma > case, it makes sense to separate the two usages into their own functions. > > Doing this also provide self-documentation as to the intent of the caller - > are they doing something rather unusual or are they simply doing a standard > kernel page table walk? > > We therefore establish two separate functions - walk_page_range_debug() for > this single usage, and walk_kernel_page_table_range() for general kernel > page table walking. > > We additionally make walk_page_range_debug() internal to mm. > > Note that ptdump uses the precise same function for kernel walking as a > convenience, so we permit this but make it very explicit by having > walk_page_range_novma() invoke walk_kernel_page_table_range() in this case. > > Signed-off-by: Lorenzo Stoakes > Acked-by: Mike Rapoport (Microsoft) Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE Labs