From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yb1-f202.google.com (mail-yb1-f202.google.com [209.85.219.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0ABB814B817 for ; Thu, 22 Feb 2024 18:43:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708627414; cv=none; b=ke+jZYTcUU6VrAi1KVTgNqe+nFDlL3LxCSaiqjgugiqp7kmj1FJO1WA+o0ZSvKo0KsKGM3c3tk4rjRaNcFyTG9lVoO3aBFQ6ls6LSN2O76plGUaJ6DmzWwXvF5mLq3G2WhZ4hVvuQasA/hOIoRwPhbPdLE5nZ2k5CIbH33zGc4M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708627414; c=relaxed/simple; bh=8NLzBUI9VMl4Y6yjlgAyBN2B5MIctTr3P4tBWjtWL8E=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=ON5mGw7kWzI9/msFOlOO5z/edMDciKLnO6CCGS7eB0Q+JruGAdaVa1uhShyH9/97tUcXq+yYV0SPQbRJKYArHOanok9xPeB7AnzCXoWD69dCp3q/aFdizednAheVMi60rITjgWcGjbYN3S8gEugPIMP+N0hYrBuC2KffVbhCuIs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--yosryahmed.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=SPxMkg3Z; arc=none smtp.client-ip=209.85.219.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--yosryahmed.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="SPxMkg3Z" Received: by mail-yb1-f202.google.com with SMTP id 3f1490d57ef6-dcc05887ee9so1439276.1 for ; Thu, 22 Feb 2024 10:43:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1708627412; x=1709232212; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=vtwP2XS9ou6pEJ1RLzQIqe0uI1z5AHU3SBLD09pMwP4=; b=SPxMkg3ZoRu6qf/ymMZFaetJEW9dHNeMKbOs3wPiz3VcPCBdaaptQkiyrmR54E2iin qJcKlHp8bbRbV54cs5boido6xR59E6gYiVZJ5sNkffJiAgPNfvWqX/uojtAoZwMfhvU6 MoauX0DRcutXG6Js4GXhcVsvbrttXICAtS4LGlrir3/eKGHz4gm8sfeoVZZGYGTzI6Vm A5/xvaTEV5GB0uEmjL7D6v0L2az3cR7tAZzy9z0hGtbcK77dEdYORHnqzFTM9bqVbG0/ ENBVZDMTfkfZLO9kPrezglCfgQwojY0lvVbNx/hw2BayV38rd2A0oJAqwKlCtb+yjM3u YPqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1708627412; x=1709232212; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=vtwP2XS9ou6pEJ1RLzQIqe0uI1z5AHU3SBLD09pMwP4=; b=pU97jzxiSisOlBiKf+6nqqNLTRXaZcb4fFJdkEAIj/ymcDfE6YmkKlUvINDC7VJTNS duWO0jdaOLQe4aPDvmie90VTZFvx+Y1f61MmLsgVNhzFbYX9s6d7YZvJ4Tgz8CjRaq4x cjgcJ1slTTAUBPJBz9Jk52ayeaoJYLLZJ/Lg4er1YRyxt339SryC9caIO74tRP8ATKp3 6M0noXKhAIhFEZXEMqsQ3b5E5w1j3Kv5GZyAbroXIhFBgst/ppzFVgs0POTqnIQRFQOm BrpcVteiCg6RnAFTvVbXkK1aSJ7yhTtPzNYhzBQpZrvgg1yCFrZT8Qk/FeAu6b2CQfoD PH0Q== X-Forwarded-Encrypted: i=1; AJvYcCXtUdAwQcxhRKKPujbx91qrXAn+qDeiA49G8LA0AEHPhFBtnaBDxY/G7R0xAeCi3GFgFn1eR597Wgiy3hwcWvbmsH23xOtYCvdkSk9w X-Gm-Message-State: AOJu0Yy4F7E4BwnaQ4+Ob34zIKWFUyK+WoHJJ6XSaPYhVnrdsS9Nvteb op5bRBswBxUMXxbj89x0A9pdBLZNPnvtW1xacnOfOyVqZEq1HyhgLJkmvjPhQlMz0yZGRsuojs7 7FVsMKtrhwxZm8hr2Hg== X-Google-Smtp-Source: AGHT+IG0Dpc0HqUIEH2QaxU8zdGkOicjs62MCVp5oWNs1mYFM729U+8fzSFZDybDPzCTW48XhDCgyw3UZZzaymK9 X-Received: from yosry.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:29b4]) (user=yosryahmed job=sendgmr) by 2002:a05:6902:1245:b0:dbe:30cd:8fcb with SMTP id t5-20020a056902124500b00dbe30cd8fcbmr219ybu.0.1708627411906; Thu, 22 Feb 2024 10:43:31 -0800 (PST) Date: Thu, 22 Feb 2024 18:43:30 +0000 In-Reply-To: <88cb9996-0e9b-49ec-bc94-f816a5b64870@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240126080644.1714297-1-yosryahmed@google.com> <20240126080644.1714297-2-yosryahmed@google.com> <88cb9996-0e9b-49ec-bc94-f816a5b64870@intel.com> Message-ID: Subject: Re: [PATCH 2/2] x86/mm: clarify "prev" usage in switch_mm_irqs_off() From: Yosry Ahmed To: Dave Hansen Cc: Ingo Molnar , Thomas Gleixner , Borislav Petkov , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Andrew Morton , x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Thu, Feb 22, 2024 at 08:48:17AM -0800, Dave Hansen wrote: > 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. > */ Yes, this is more clear, thanks! However, Andrew already merged that patch into mm-stable, so it cannot be amended. I can send a separate patch to rewrite the comment tho if you'd like, WDYT? > > 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: Agreed. I can also send a separate patch for this. Thanks! > > > 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); > > } >