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Mon, 02 Dec 2024 22:12:48 -0800 (PST) Received: from pc636 ([2001:9b1:d5a0:a500::800]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-53df644322asm1695967e87.82.2024.12.02.22.12.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Dec 2024 22:12:47 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 3 Dec 2024 07:12:45 +0100 To: Ze Zuo Cc: gustavoars@kernel.org, akpm@linux-foundation.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org, keescook@chromium.org, urezki@gmail.com, wangkefeng.wang@huawei.com Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the vmalloc check. Message-ID: References: <20241203023159.219355-1-zuoze1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241203023159.219355-1-zuoze1@huawei.com> X-Rspamd-Server: rspam05 X-Stat-Signature: bmkdtgohirrr54aqhxnk33bdcfupjwsg X-Rspamd-Queue-Id: 5F7F8180012 X-Rspam-User: X-HE-Tag: 1733206357-671191 X-HE-Meta: U2FsdGVkX18E7Tw/1bnBjy0hAto3eZ7wpp3mh8/fBZRDqd2kPLPUmEHXgSQ9jSYBFCphWEcEMy8EtvmoTxz6gmX+AnIIFXtC00WMJ4pQMbhBpoZ4wFsiRDzpS7urEkQCPFy8o23PA5PVMfelfyAFvPFdizyRXg6/e19cQ47DNLd1TCY9zjefS6BgTV2YRxQUEvizrQdOpVD6i+fs+xfgMivpRGJqn7qwSb1hZ1gr+rEqSgwU2JgtW3V4m6r4jtdjFeNefA/i6GwUMHp4j2RpJG9lqhfKXPyJWR1IPQVmJ3PBHAyrTaVOyl3l7TYI9HDPXM9e6fghJhTJ/a0k4VEjBE6qPTrb+s0+FmRm5ZO9gtInS1a3Vws27RUXctQEaD0L4DXzq2geJvKVv/lpNc+HZPWUGksnWPP4drcO45/amMBaNApxG7NDEU/y3mgam8dJRWaurNJ7/tMROucnAwJTI8ztMZUNpG305je7dCSZ6cG929B+Th05oJR+5uuZflokrrKseZLRByqyXz3qchGyIrSegAyhM6sA2yIvDC/fjieWeokLbSxKjtkisBWSa9Eyi6MRN48MJgdLIcNdDejSm6du4PqFJlTu3FvaNXnQiXARizMf5WPZRR5tjvMaqxC0uFQJ4t44Sl6rvQGZ4MP95JXXl9CHotB7d3Kx9SbhDXf6ih4qtEHfl7pY4sDxZlv85DoppSv1RgdHrm5dIwvRDmgr8boviNd2857rkdMaDooFmzVNaMfN29iUa8eDqrmlIyBvtLwAC+AY+ZH2BJRMqzZxCsSziHr3LCt4l6HVcuBiEmtHCc0B2/jGEOCRipC5erL7FpNG+0XFNijJBimdx1riaH5DMLM+0blBn6wGwpSX4J3J+dPf3jqzSCD4ucelJXZzHGnpvHgI4PV9u+N9cfYf8K4+L9AsF7VZswJ9pdyXj/AX/iwVdFqBCiPDMLQJwf7VEdZpV3i2/mKHBmz sWBdyfm1 sWrlPsyEhTVe/eT6KhFmdrJlvcxVpXxkCAxEup2lppQZ0c4LGuW4mMZWAUKYy0LZmcJXwZ998MiCejQBKlHlQIMhUfkyl70afM/hN5skOehYrexNSJB4GuUJUZ3YJq0l+RHWGAzyJXIVgyulKTEXe+D01QpmKBi33Oy1vz9BJe4ymzK7uqsliThfRsf/JgKH+dCL7/YLwY+XGnWJymxIlP4IE5qXUCRwc5fk1jMTq1uUEl9JEdahraMY/hXiOTPIIaHEL64U8Ist5qe6zHKsTz+ZyqNSxhHBchZIBjOBgW46idbtbhVmqrbNq0jfy1ZKMtgm5+Luc6r/MJWx0ubFyHtU0SrvudkIefqjS1dLPpztSppHZcd3PUAw2VQOtQvpoAAmRkcR+kZnG0ej2kjlOOtmf+5dtMeU70TAflNuY+nDWlB6dDkvbiH5BWg== 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 Tue, Dec 03, 2024 at 10:31:59AM +0800, Ze Zuo wrote: > The commit 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns") introduced > vmalloc check for usercopy. However, in subsystems like networking, when > memory allocated using vmalloc or vmap is subsequently copied using > functions like copy_to_iter/copy_from_iter, the check is triggered. This > adds overhead in the copy path, such as the cost of searching the > red-black tree, which increases the performance burden. > > We found that after merging this patch, network bandwidth performance in > the XDP scenario significantly dropped from 25 Gbits/sec to 8 Gbits/sec, > the hardened_usercopy is enabled by default. > > To address this, we introduced a debugfs interface that allows selectively > enabling or disabling the vmalloc check based on the use case, optimizing > performance. > > By default, vmalloc check for usercopy is enabled. > > To disable the vmalloc check: > echo Y > /sys/kernel/debug/bypass_usercopy_vmalloc_check > > After executing the above command, the XDP performance returns to 25 > Gbits/sec. > To what Matthew has asked, could you please also specify the kernel version you run your experiment on? Apart of that please describe your system and HW. Thank you! -- Uladzislau Rezki