From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 08A74C36002 for ; Wed, 9 Apr 2025 15:39:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=STjRVpgg0Yp0bRazVRJxjrVKHPO2bSZ4lShot4vAUzA=; b=1ezwLberexJkElcuiSDB3IdYkc or37LseKIAaYqFvPuzjsCWLnn+HQpRMy2Uw8BC5LyfCj0Iysimwcv1FShAQC5ks8p1ZsG0t3gSDtX 1aoPtERn7GVBPgPAkyu/oBbwZogMzkQPG7RFEBJWTjlHpzriojvzSHysnmL5ufvEDsnY7xfyWTU7k 5Yb0ZnFAro4365TGtTUFu51OGtzEX8bn+W25Y3vAPvAG0Q6KteDaGNoZTPuXkHzZfqbkuku1PLqW0 ZbaH4lVQEJZKb9um+6WoIl2WhfAxn8IhTRtpCLltQQkSYCfEuLnjm+CZQ+l11UXnToKLo1qGiBaRJ lb97GlNw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1u2XWK-00000007iuT-18Wq; Wed, 09 Apr 2025 15:39:20 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1u2XTp-00000007iLf-0uMj for linux-arm-kernel@lists.infradead.org; Wed, 09 Apr 2025 15:36:46 +0000 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 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250409_083645_297834_2D706FA1 X-CRM114-Status: GOOD ( 13.05 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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