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[95.203.13.87]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-2ffdfbef4aasm18466261fa.34.2024.12.04.00.51.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Dec 2024 00:51:10 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 4 Dec 2024 09:51:07 +0100 To: Matthew Wilcox Cc: Uladzislau Rezki , Kefeng Wang , zuoze , gustavoars@kernel.org, akpm@linux-foundation.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, keescook@chromium.org Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the vmalloc check. Message-ID: References: <92768fc4-4fe0-f74a-d61c-dde0eb64e2c0@huawei.com> <76995749-1c2e-4f78-9aac-a4bff4b8097f@huawei.com> Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: > On Tue, Dec 03, 2024 at 08:02:26PM +0100, Uladzislau Rezki wrote: > > I think there are a few other things we can try here. > > First, if the copy is small (and I still don't have an answer to that > ...), we can skip the vmalloc lookup if the copy doesn't cross a page > boundary. > I noticed that, a path which is in question, does not supply a starting address of mapping area, instead it passes something within. > > Second, we could try storing this in a maple tree rather than an rbtree. > That gives us RCU protected lookups rather than under a spinlock. > I think, when i have more free cycles, i will check it from performance point of view. Because i do not know how much a maple tree is efficient when it comes to lookups, insert and removing. As an RCU safe data structure, yes, a searching is improved in a way there is no need in taking spinlock. As a noted earlier i do not know if a maple tree allows to find a data when instead of key, it is associated with, we pass something that is withing a searchable area: [va_start:va_end]. -- Uladzislau Rezki