From nobody Sun Feb 8 09:16:54 2026 Received: from mail-yb1-f201.google.com (mail-yb1-f201.google.com [209.85.219.201]) (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 D8D2649626 for ; Sat, 10 Aug 2024 00:59:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723251556; cv=none; b=pZ8lr19v/NFCvNTxt4UZTKxsglDTRwyPvdjYNXfnYudtsnkDet1SH95Sob9Qls8RsRabY4URe7UIS61i8pwJCY9T7yj507mu80b/ovj3iw/aV/jSvS1vU9PVkFymgeLU622JdJ/mCMn8TIluBr4WVyilIbQSQZqHxFVBudsp4RM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723251556; c=relaxed/simple; bh=Qd7PQGlgqKWRuWWjokUhPdESXuWBLnqq7/eOi/nr0rQ=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=m1cRdANXjWY3Nwk/KtAMVUYmCNXjz4irpEUbrsz6yoR0QvwZEuId9QRLvXQlPNUXhofA4bcH5ijonIBstNVmNR5KU8kpvAlh39dhPwDc2m0QDFpuimNxX2Iq+H08hkogsJMLSSL0I241KWvOxdQZYfCbcJRKEGSpiXsUlrctwVc= 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=n6aVO0jN; arc=none smtp.client-ip=209.85.219.201 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="n6aVO0jN" Received: by mail-yb1-f201.google.com with SMTP id 3f1490d57ef6-e0b3742b309so4369027276.1 for ; Fri, 09 Aug 2024 17:59:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1723251554; x=1723856354; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=hzRe7SJD/obU3/qfFI0GbsgavYc/p8tTU00CB2noSOQ=; b=n6aVO0jNtyeSS67c4MLhlFLx56vU5XFqtn10BsfgY+Tt7ujnpB00eZRU7lHOPWztGZ C7+A7IFxM6h557icDAb+oBGUIybR4X51I8JWZ9cmQ1Wpjwe09n805U6Bvwy7blxAuQyD NK6u6DtjYU++XLgDikOUvzVyDDC+S/G8t6LljZ6P1ojQbwa838i8IPx1pQQ32l0ZaOr4 h/5rti47t1ynIy5GYiC682tRcvu6b9J19DqgWf5ovGmqymDx72Jkrzs6PmOwBGP7E45M SvpuphQ09vJB5RoggTnB7gghoO4qPMMCWAN5RRv0FcDqBZti6m3kf7OZBko7UjcHtda/ VZGA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1723251554; x=1723856354; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=hzRe7SJD/obU3/qfFI0GbsgavYc/p8tTU00CB2noSOQ=; b=ZxLHwsy862vCoNHiyt2Upmf42wDg7LwDp8hI8XWmY43992sml9LDgdfLUn3UiVeCTx vz2etEtAnwvpjZIOPPcToYOqmaATxu5tlb7+5j/2JuGYt8rmBsBHJ8IEnTuEH0ME+2E/ E5Mgk3aS+0uavg+3HE5EHC6Le8VP+ccTylhLHZY/5WNZr7dndzNP/VfpB8WKeR1IHNUT XXGiS93YY758kNSFjEkapyER7LNDbnNbEjRZAEoTUxVye9puZi6+4P9qbv5Tpo/Eq0fY i36br22Zx0vMmbCeJIbw94wmal3aMrAuNA+T/koR3WvYvmeoL869B3VQjl3MKlIhltf4 cqnQ== X-Forwarded-Encrypted: i=1; AJvYcCWOOCkVWI6yN4R25O9gLFOo+QAbY8J6NHJu7FlDi1biLXuhrlzCMWxQiwK1DArWSBzuuYpHaktGh0DDZMP0/iN8VqHCwphWxJv902ZU X-Gm-Message-State: AOJu0YwtwE7nErHgnV/r9zHbxveWOk9TmRwlHR9t+eMg3ob1raSHeniB aM587uhsic5l+gp5D9HFm/k+FBPBK4kQ8Bbq+zPdXZ2qr35HE8W3zmiqEch3zklpxBoslLeXeph 1z7CxN2x9WSlzqreB+A== X-Google-Smtp-Source: AGHT+IHD0Iz9jlKUFUJREyIgq4IGjnZvc8Lz0nEksZRzwjg7ycn2KRHYS2pQ8au66FNFZ3hf1c2NXmzyd8oafA1x X-Received: from yosry.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:29b4]) (user=yosryahmed job=sendgmr) by 2002:a5b:c4b:0:b0:e0b:f684:e972 with SMTP id 3f1490d57ef6-e0eb9a32f37mr29248276.12.1723251553634; Fri, 09 Aug 2024 17:59:13 -0700 (PDT) Date: Sat, 10 Aug 2024 00:59:11 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.46.0.76.ge559c4bf1a-goog Message-ID: <20240810005911.684644-1-yosryahmed@google.com> Subject: [PATCH] dma-mapping: use bit masking to check VM_DMA_COHERENT From: Yosry Ahmed To: Christoph Hellwig , Marek Szyprowski , Robin Murphy Cc: iommu@lists.linux.dev, Reiji Watanabe , linux-kernel@vger.kernel.org, Yosry Ahmed Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" In dma_common_find_pages(), area->flags are compared directly with VM_DMA_COHERENT. This works because VM_DMA_COHERENT is the only set flag. During development of a new feature (ASI [1]), a new VM flag is introduced, and that flag can be injected into VM_DMA_COHERENT mappings (among others). The presence of that flag caused dma_common_find_pages() to return NULL for VM_DMA_COHERENT addresses, leading to a lot of problems ending in crashing during boot. It took a bit of time to figure this problem out. It was a mistake to inject a VM flag to begin with, but it took a significant amount of debugging to figure out the problem. Most users of area->flags use bitmasking rather than equivalency to check for flags. Update dma_common_find_pages() and dma_common_free_remap() to do the same, which would have avoided the boot crashing. Instead, add a warning in dma_common_find_pages() if any extra VM flags are set to catch such problems more easily during development. No functional change intended. [1]https://lore.kernel.org/lkml/20240712-asi-rfc-24-v1-0-144b319a40d8@googl= e.com/ Signed-off-by: Yosry Ahmed --- kernel/dma/remap.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/dma/remap.c b/kernel/dma/remap.c index 27596f3b4aef3..9e2afad1c6152 100644 --- a/kernel/dma/remap.c +++ b/kernel/dma/remap.c @@ -10,8 +10,10 @@ struct page **dma_common_find_pages(void *cpu_addr) { struct vm_struct *area =3D find_vm_area(cpu_addr); =20 - if (!area || area->flags !=3D VM_DMA_COHERENT) + if (!area || !(area->flags & VM_DMA_COHERENT)) return NULL; + WARN(area->flags !=3D VM_DMA_COHERENT, + "unexpected flags in area: %p\n", cpu_addr); return area->pages; } =20 @@ -61,7 +63,7 @@ void dma_common_free_remap(void *cpu_addr, size_t size) { struct vm_struct *area =3D find_vm_area(cpu_addr); =20 - if (!area || area->flags !=3D VM_DMA_COHERENT) { + if (!area || !(area->flags & VM_DMA_COHERENT)) { WARN(1, "trying to free invalid coherent area: %p\n", cpu_addr); return; } --=20 2.46.0.76.ge559c4bf1a-goog