From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AC19026772E; Wed, 9 Apr 2025 15:36:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744213006; cv=none; b=UyP3/2gAnmjCOyWCwrILM/tIMIbFvJ3Bo+f8qnNi+D3ZFYoaGob0UG1RC4pCDteHqYhPp9F4toJlWsjQOUqtKcGkhmFUy7zpvC56IDbhw1VnKPWnbduiTqxtE1V+5OyF20dj/9FiivLwodNQelX/97p1eBbDNvp/4K9EOlFJYnA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744213006; c=relaxed/simple; bh=mra/8qKW0Evjk3Ofx4vXnWBF0Y2y8/XWWI9ZGtde6nU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bmW36qKip7sFPc5Es4uZVRujFmroYvsI9BoKkGkQy/umo4yi/kW4frENrBTnc8JIhk4/Iwy/PRo6xeB6seVqCC1j3ttuBOdMAR16M+DNoqPj3xZqt6lykY+cNFT0zKA1gvRsDg6htKVPiTrK7fDKrfd4AAWqoVgxxg7Ufq4mfuc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=Mp2nvG16; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="Mp2nvG16" Received: from [10.137.184.60] (unknown [131.107.160.188]) by linux.microsoft.com (Postfix) with ESMTPSA id DC5202114D83; Wed, 9 Apr 2025 08:36:43 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com DC5202114D83 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1744213004; bh=STjRVpgg0Yp0bRazVRJxjrVKHPO2bSZ4lShot4vAUzA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Mp2nvG161guzkA5jkhuWIpYyBT04WkL0edtyczcFZXoq8eK8Ezwe8HEmiBEcfvDCy deajHxHYyWZU7h7pWiFKRJXXcUnyRylUnG5vNOAzszEOLLM9KKKiWnfuRP81BheV+I WY2pVGQeqqiyxm/f+Q6cp3ADRSs3IuXWn24zdJDY= Message-ID: Date: Wed, 9 Apr 2025 08:36:43 -0700 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 hyperv-next 6/6] drivers: SCSI: Do not bounce-bufffer for the confidential VMBus To: Christoph Hellwig Cc: aleksander.lobakin@intel.com, andriy.shevchenko@linux.intel.com, arnd@arndb.de, bp@alien8.de, catalin.marinas@arm.com, corbet@lwn.net, dakr@kernel.org, dan.j.williams@intel.com, dave.hansen@linux.intel.com, decui@microsoft.com, gregkh@linuxfoundation.org, haiyangz@microsoft.com, hpa@zytor.com, James.Bottomley@HansenPartnership.com, Jonathan.Cameron@huawei.com, kys@microsoft.com, leon@kernel.org, lukas@wunner.de, luto@kernel.org, m.szyprowski@samsung.com, martin.petersen@oracle.com, mingo@redhat.com, peterz@infradead.org, quic_zijuhu@quicinc.com, robin.murphy@arm.com, tglx@linutronix.de, wei.liu@kernel.org, will@kernel.org, iommu@lists.linux.dev, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, x86@kernel.org, apais@microsoft.com, benhill@microsoft.com, bperkins@microsoft.com, sunilmut@microsoft.com References: <20250409000835.285105-1-romank@linux.microsoft.com> <20250409000835.285105-7-romank@linux.microsoft.com> <20250409105332.GB5721@lst.de> Content-Language: en-US From: Roman Kisel In-Reply-To: <20250409105332.GB5721@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/9/2025 3:53 AM, Christoph Hellwig wrote: > On Tue, Apr 08, 2025 at 05:08:35PM -0700, Roman Kisel wrote: >> The device bit that indicates that the device is capable of I/O >> with private pages lets avoid excessive copying in the Hyper-V >> SCSI driver. >> >> Set that bit equal to the confidential external memory one to >> not bounce buffer > > Drivers have absolutely no business telling this. The need for bounce > buffering or not is a platform/IOMMU decision and not one specific to > a certain device or driver. Seemed to work although I cannot claim nothing is going to be broken ever. It did appear from the code that one could have this per-device bit. As I understand, you're saying this is architecturally broken. Do you think a broader set of changes would improve the implementation? > -- Thank you, Roman