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Sun, 4 Feb 2024 06:03:16 -0500 (EST) Message-ID: <716af17c-136b-4852-86ce-a23bafe34fbb@flygoat.com> Date: Sun, 4 Feb 2024 11:03:15 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/3] Handle delay slot for extable lookup Content-Language: en-US To: Linus Torvalds Cc: Oleg Nesterov , Thomas Bogendoerfer , Andrew Morton , Ben Hutchings , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, Xi Ruoyao References: <20240202-exception_ip-v2-0-e6894d5ce705@flygoat.com> From: Jiaxun Yang Autocrypt: addr=jiaxun.yang@flygoat.com; keydata= xsFNBFnp/kwBEADEHKlSYJNLpFE1HPHfvsxjggAIK3ZtHTj5iLuRkEHDPiyyiLtmIgimmD3+ XN/uu2k1FFbrYiYgMjpGCXeRtdCLqkd+g9V4kYMlgi4MPHLt3XEuHcoKD1Yd2qYPT/OiQeGM 6bPtGUZlgfOpze1XuqHQ2VMWATL+kLYzk6FUUL715t8J5J9TgZBvSy8zc6gvpp3awsCwjFSv X3fiPMTC2dIiiMh4rKQKGboI1c7svgu6blHpy/Q5pXlEVqfLc7tFTGnvUp95jsK639GD8Ht3 0fSBxHGrTslrT775Aqi+1IsbJKBOmxIuU9eUGBUaZ00beGE09ovxiz2n2JKXKKZklNqhzifb 6uyVCOKdckR8uGqzRuohxDS7vlDZfFD5Z5OhplFY/9q+2IjCrWMmbHGSWYs9VV52XGM+wiEG sM5bup03N2q1kDXUWJ+zNNYowuOJKN9uxF3jBjdXSDi3uJu/ZUL/mBqI58SkHq5NTaHypRoE 5BxVmgDMCGQe93adKHUNmt4HK28R506S7019+umg1bq5vA/ncmh/J2k8MFGPXqO8t1xVI2O5 qrRheRKu1oST46ZJ7vKET1UwgcXTZ1iwqFlA26/iKxXoL7R7/AqWrapokEsUzRblGcutGZ/b 4lJVOxxAWaRcajpWvwqscI2mUF++O7DxYbhOJ/EFY2rv0i6+/QARAQABzSVKaWF4dW4gWWFu ZyA8amlheHVuLnlhbmdAZmx5Z29hdC5jb20+wsGRBBMBCAA7AhsjAh4BAheABQsJCAcCBhUK CQgLAgQWAgMBFiEEmAN5vv6/v0d+oE75wRGUkHP8D2cFAmKcjj8CGQEACgkQwRGUkHP8D2fx LxAAuNjknjfMBXIwEDpY+L2KMMU4V5rvTBATQ0dHZZzTlmTJuEduj/YdlVo0uTClRr9qkfEr Nfdr/YIS6BN6Am1x6nF2PAqHu/MkTNNFSAFiABh35hcm032jhrZVqLgAPLeydwQguIR8KXQB pP6S/jL3c7mUvVkoYy2g5PE1eH1MPeBwkg/r/ib9qNJSTuJH3SXnfZ4zoynvf3ipqnHsn2Sa 90Ta0Bux6ZgXIVlTL+LRDU88LISTpjBITyzn5F6fNEArxNDQFm4yrbPNbpWJXml50AWqsywp q9jRpu9Ly4qX2szkruJ/EnnAuS/FbEd4Agx2KZFb6LxxGAr4useXn6vab9p1bwRVBzfiXzqR WeTRAqwmJtdvzyo3tpkLmNC/jC3UsjqgfyBtiDSQzq0pSu7baOjvCGiRgeDCRSWq/T3HGZug 02QAi0Wwt/k5DX7jJS4Z5AAkfimXG3gq2nhiA6R995bYRyO8nIa+jmkMlYRFkwWdead3i/a0 zrtUyfZnIyWxUOsqHrfsN45rF2b0wHGpnFUfnR3Paa4my1uuwfp4BI6ZDVSVjz0oFBJ5y39A DCvFSpJkiJM/q71Erhyqn6c1weRnMok3hmG0rZ8RCSh5t7HllmyUUWe4OT97d5dhI7K/rnhc ze8vkrTNT6/fOvyPFqpSgYRDXGz2qboX/P6MG3zOOARlnqgjEgorBgEEAZdVAQUBAQdAUBqi bYcf0EGVya3wlwRABMwYsMimlsLEzvE4cKwoZzEDAQgHwsF2BBgBCAAgFiEEmAN5vv6/v0d+ oE75wRGUkHP8D2cFAmWeqCMCGwwACgkQwRGUkHP8D2dXlw/8CGKNXDloh1d7v/jDgcPPmlXd lQ4hssICgi6D+9aj3qYChIyuaNncRsUEOYvTmZoCHgQ6ymUUUBDuuog1KpuP3Ap8Pa3r5Tr6 TXtOl6Zi23ZWsrmthuYtJ8Yn5brxs6KQ5k4vCTkbF8ukue4Xl4O0RVlaIgJihJHZTfd9rUZy QugM8X98iLuUqYHCq2bAXHOq9h+mTLrhdy09dUalFyhOVejWMftULGfoXnRVz6OaHSBjTz5P HwZDAFChOUUR6vh31Lac2exTqtY/g+TjiUbXUPDEzN4mENACF/Aw+783v5CSEkSNYNxrCdt8 5+MRdhcj7y1wGfnSsKubHTOkBQJSanNr0cZZlPsJK0gxB2YTG6Nin13oX8mV7sAa3vBqqwfj ZtjNA+Up9IJY4Iz5upykUDAtCcvm82UnJoe5bMuoiyVccuqd5K/058AAxWv8fIvB4bSgmGMM aAN9l7GLyi4NhsKCCcAGSc2YAsxFrH6whVqY6JIF+08n1kur5ULrEKHpTTeffwajCgZPWpFc 7Mg2PDpoOwdpKLKlmIpyDexGVH0Lj/ycBL8ujDYZ2tA9HhEaO4dW6zsQyt1v6mZffpWK+ZXb Cs8oFeACbrtNFF0nhNI6LUPH3oaVOkUoRQUYDuX6mIc4VTwMA8EoZlueKEHfZIKrRf2QYbOZ HVO98ZmbMeg= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2024/2/4 07:41, Linus Torvalds 写道: [...] > The thing is, the only reason for the code in > get_mmap_lock_carefully() is for kernel bugs. IOW, some kernel bug > with a wild pointer, and we do not want to deadlock on the mm > semaphore, we want to get back to the fault handler and it should > report an oops. > > ... and one of the "wild pointers" might in fact be the instruction > pointer, in case we've branched through a NULL function pointer or > similar. IOW, the exception *source* might be the instruction pointer > itself. Well this is the tricky part of my assumption. In `exception_epc()` `__isa_exception_epc()` stuff is only called if we are in delay slot. It is impossible for a invalid instruction_pointer to be considered as "in delay slot" by hardware. I'd agree that sounds fragile though. Thanks > > So I realy think that MIPS needs to have some kind of "safe kernel > exception pointer" helper. One that is guaranteed not to fault when > evaluating the exception pointer. > > Assuming the kernel itself is never built with MIPS16e instructions, > maybe that's a safe assumption thanks to the "get_isa16_mode()" check > of EPC. But all of this makes me nervous. > > Linus -- --- Jiaxun Yang