From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C714963CB for ; Fri, 24 May 2024 01:10:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716513005; cv=none; b=Z7eqXr+sEHB+dlp3k3wSkYzdLFCtypvkaGahIfkZOcY1Zg+Yi0ItO9rAyjdmKFHXgRvbEN6dJ46SQvzKECZPCOZhRzwjVZOIIxEu2wvsyknFyRjI9FMKbW77KsjUhZ411fWnsMHxEz+NwBXAMSMoo6poxCRD/PBK0x4SVinsbV8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1716513005; c=relaxed/simple; bh=9zABepybl5Xgb4WhZA5zrlZW3sm8pmuNcyyKqdDjNS4=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=RKv+SZLy8MsQFmnKbcxS2B6bpVZNNlHyPb9H1LZ1oqjaroux4oNBHg/9OndBEG6BPBS0h+oww5hqy1WuM4l+1l27aGifaA9VyM7sBtPD6AH9g7F+UskHvZV2D6tPwWMEY31uTsYIHxzakUJ+YpntyQzepQa4202itc/0rb0PbXI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=DK5VZN6k; arc=none smtp.client-ip=198.175.65.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="DK5VZN6k" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1716513004; x=1748049004; h=message-id:date:mime-version:cc:subject:to:references: from:in-reply-to:content-transfer-encoding; bh=9zABepybl5Xgb4WhZA5zrlZW3sm8pmuNcyyKqdDjNS4=; b=DK5VZN6k3femHbGi+X8L/hKRLIAv1H8lua4wQFTd9+fMcUKlfCAfjOBS xZ8ZoJjESAnkQ5yXo3qVguzL3OZalo/XpQQA/Dzc2l3xcmV+xohazXFKZ jAaCFfcLERI4mnV4YVjKKa2Q2hE+adqHg817B1O25CFAyTmWQR2FUHT/U eRoUnz/ODH9RHJK1Twbh4HX6XnsUzYMYHtwkbP4rePB/cVIdWD+JnR+dF pL96Um7h1TH5EesHqD51htp1H5yf6323tIeKwsZ7wAGYQ1f9Fe2QuzJWF ynLfFnwtGI/5+n2hVEYmICkxcCYBiPE9dMKwHZZ2oiAeZ0kqnFzzCSN/x g==; X-CSE-ConnectionGUID: kv++gFWsSfGFvSEuHmMIwg== X-CSE-MsgGUID: 07d4GZTaRAyZynor4Q3rxg== X-IronPort-AV: E=McAfee;i="6600,9927,11081"; a="16662216" X-IronPort-AV: E=Sophos;i="6.08,184,1712646000"; d="scan'208";a="16662216" Received: from fmviesa001.fm.intel.com ([10.60.135.141]) by orvoesa107.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 May 2024 18:10:03 -0700 X-CSE-ConnectionGUID: g7IsVQLASryIB31Jt5lnsw== X-CSE-MsgGUID: VClbEt7rTEarGLeuFs+a+g== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.08,184,1712646000"; d="scan'208";a="65065176" Received: from unknown (HELO [10.239.159.127]) ([10.239.159.127]) by fmviesa001.fm.intel.com with ESMTP; 23 May 2024 18:10:01 -0700 Message-ID: Date: Fri, 24 May 2024 09:08:04 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: baolu.lu@linux.intel.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, David Woodhouse , Joerg Roedel , Will Deacon , Robin Murphy Subject: Re: [PATCH 2/3] iommu/vt-d: Use try_cmpxchg64() in intel_pasid_get_entry() To: Uros Bizjak References: <20240522082729.971123-1-ubizjak@gmail.com> <20240522082729.971123-2-ubizjak@gmail.com> Content-Language: en-US From: Baolu Lu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/23/24 9:57 PM, Uros Bizjak wrote: > On Thu, May 23, 2024 at 3:44 PM Baolu Lu wrote: >> On 2024/5/23 21:34, Uros Bizjak wrote: >>>>> + if (!try_cmpxchg64(&dir[dir_index].val, &tmp, >>>>> + (u64)virt_to_phys(entries) | PASID_PTE_PRESENT)) { >>>> Above change will cause a dead loop during boot. It should be >>> No, it is correct as written: >>> >>> if (cmpxchg64(*ptr, 0, new)) >>> >>> can be written as: >>> >>> if (cmpxchg64(*ptr, 0, new) != 0) >>> >>> this is equivalent to: >>> >>> tmp = 0ULL; >>> if (!try_cmpxchg64(*ptr, &tmp, new)) >> The return value of both cmpxchg64() and try_cmpxchg64() is the old >> value that was loaded from the memory location, right? > Actually, try_cmpxchg() returns true if successful and false if it fails. Oh! I misunderstood this. > > tmp = 0ULL; > if (!try_cmpxchg64(*ptr, &tmp, new)) > > The logic in the above snippet can be interpreted as: > > if we fail to compare *ptr with 0, then: > > iommu_free_page(entries); > goto retry; > > as intended in the original code. Okay, it's fine. Best regards, baolu