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Wed, 16 Nov 2022 10:28:22 +0000 (UTC) Received: from t480s.fritz.box (unknown [10.39.193.216]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3E25A2024CCA; Wed, 16 Nov 2022 10:28:16 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Subject: [PATCH mm-unstable v1 08/20] mm: extend FAULT_FLAG_UNSHARE support to anything in a COW mapping Date: Wed, 16 Nov 2022 11:26:47 +0100 Message-Id: <20221116102659.70287-9-david@redhat.com> In-Reply-To: <20221116102659.70287-1-david@redhat.com> References: <20221116102659.70287-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, Greg Kroah-Hartman , David Hildenbrand , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, Nadav Amit , linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org, Shuah Khan , Andrea Arcangeli , linux-samsung-soc@vger.kernel.org, linux-rdma@vger.kernel.org, David Airlie , x86@kernel.org, Hugh Dickins , Matthew Wilcox , Christoph Hellwig , Jason Gunthorpe , Vlastimil Babka , linux-media@vger.kernel.org, Arnd Bergmann , John Hubbard , linux-um@lists.infradead.org, etnaviv@lists.freedesktop.org, Alex Williamson , Peter Xu , Muchun Song , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, Oded Gabbay , linux-mips@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-security-module@vger.kernel.org, linux-alpha@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Lucas Stach , Linus Torvalds , Mike Kravetz Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Extend FAULT_FLAG_UNSHARE to break COW on anything mapped into a COW (i.e., private writable) mapping and adjust the documentation accordingly. FAULT_FLAG_UNSHARE will now also break COW when encountering the shared zeropage, a pagecache page, a PFNMAP, ... inside a COW mapping, by properly replacing the mapped page/pfn by a private copy (an exclusive anonymous page). Note that only do_wp_page() needs care: hugetlb_wp() already handles FAULT_FLAG_UNSHARE correctly. wp_huge_pmd()/wp_huge_pud() also handles it correctly, for example, splitting the huge zeropage on FAULT_FLAG_UNSHARE such that we can handle FAULT_FLAG_UNSHARE on the PTE level. This change is a requirement for reliable long-term R/O pinning in COW mappings. Signed-off-by: David Hildenbrand --- include/linux/mm_types.h | 8 ++++---- mm/memory.c | 4 ---- 2 files changed, 4 insertions(+), 8 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 5e7f4fac1e78..5e9aaad8c7b2 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1037,9 +1037,9 @@ typedef struct { * @FAULT_FLAG_REMOTE: The fault is not for current task/mm. * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch. * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals. - * @FAULT_FLAG_UNSHARE: The fault is an unsharing request to unshare (and mark - * exclusive) a possibly shared anonymous page that is - * mapped R/O. + * @FAULT_FLAG_UNSHARE: The fault is an unsharing request to break COW in a + * COW mapping, making sure that an exclusive anon page is + * mapped after the fault. * @FAULT_FLAG_ORIG_PTE_VALID: whether the fault has vmf->orig_pte cached. * We should only access orig_pte if this flag set. * @@ -1064,7 +1064,7 @@ typedef struct { * * The combination FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE is illegal. * FAULT_FLAG_UNSHARE is ignored and treated like an ordinary read fault when - * no existing R/O-mapped anonymous page is encountered. + * applied to mappings that are not COW mappings. */ enum fault_flag { FAULT_FLAG_WRITE = 1 << 0, diff --git a/mm/memory.c b/mm/memory.c index d47ad33c6487..56b21ab1e4d2 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3432,10 +3432,6 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) } wp_page_reuse(vmf); return 0; - } else if (unshare) { - /* No anonymous page -> nothing to do. */ - pte_unmap_unlock(vmf->pte, vmf->ptl); - return 0; } copy: /* -- 2.38.1