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X-IronPort-AV: E=McAfee;i="6600,9927,10992"; a="25320203" X-IronPort-AV: E=Sophos;i="6.06,179,1705392000"; d="scan'208";a="25320203" Received: from orviesa003.jf.intel.com ([10.64.159.143]) by orvoesa101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Feb 2024 08:48:19 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.06,179,1705392000"; d="scan'208";a="10229282" Received: from jwbates1-mobl.amr.corp.intel.com (HELO [10.209.48.22]) ([10.209.48.22]) by ORVIESA003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Feb 2024 08:48:20 -0800 Message-ID: <88cb9996-0e9b-49ec-bc94-f816a5b64870@intel.com> Date: Thu, 22 Feb 2024 08:48:17 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] x86/mm: clarify "prev" usage in switch_mm_irqs_off() Content-Language: en-US To: Yosry Ahmed , Ingo Molnar Cc: Thomas Gleixner , Borislav Petkov , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Andrew Morton , x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240126080644.1714297-1-yosryahmed@google.com> <20240126080644.1714297-2-yosryahmed@google.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 0A8EC160007 X-Stat-Signature: ck59ow5omyoxy8kat173w9wcso44brhd X-Rspam-User: X-HE-Tag: 1708620500-198376 X-HE-Meta: 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 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 1/26/24 00:06, Yosry Ahmed wrote: > +/* > + * The "prev" argument passed by the caller does not always match CR3. For > + * example, the scheduler passes in active_mm when switching from lazy TLB mode > + * to normal mode, but switch_mm_irqs_off() can be called from x86 code without > + * updating active_mm. Use cpu_tlbstate.loaded_mm instead. > + */ > +void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, > struct task_struct *tsk) One nit here: It's not obvious that "unused" is 'the "prev" argument'. Would something like this be more clear? /* * This optimizes when not actually switching mm's. Some architectures * use the 'unused' argument for this optimization, but x86 must use * 'cpu_tlbstate.loaded_mm' instead because it does not always keep * ->active_mm up to date. */ Also, I think it might be useful to have the rule that arch/x86 code _always_ calls switch_mm_irqs_off() with the first argument (the newly-named 'unused') set to NULL. I think there's only one site: > void switch_mm(struct mm_struct *prev, struct mm_struct *next, > struct task_struct *tsk) > { > unsigned long flags; > > local_irq_save(flags); > switch_mm_irqs_off(prev, next, tsk); > local_irq_restore(flags); > }