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([2404:f801:9000:18:efec::50b]) by smtp.gmail.com with ESMTPSA id d10sm6777113pfl.139.2021.12.09.03.17.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Dec 2021 03:17:16 -0800 (PST) Message-ID: Date: Thu, 9 Dec 2021 19:17:08 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH V6 4/5] scsi: storvsc: Add Isolation VM support for storvsc driver Content-Language: en-US To: Long Li , KY Srinivasan , Haiyang Zhang , Stephen Hemminger , "wei.liu@kernel.org" , Dexuan Cui , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "davem@davemloft.net" , "kuba@kernel.org" , "jejb@linux.ibm.com" , "martin.petersen@oracle.com" , "arnd@arndb.de" , "hch@infradead.org" , "m.szyprowski@samsung.com" , "robin.murphy@arm.com" , Tianyu Lan , "thomas.lendacky@amd.com" , "Michael Kelley (LINUX)" Cc: "iommu@lists.linux-foundation.org" , "linux-arch@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "netdev@vger.kernel.org" , vkuznets , "brijesh.singh@amd.com" , "konrad.wilk@oracle.com" , "hch@lst.de" , "joro@8bytes.org" , "parri.andrea@gmail.com" , "dave.hansen@intel.com" References: <20211207075602.2452-1-ltykernel@gmail.com> <20211207075602.2452-5-ltykernel@gmail.com> From: Tianyu Lan In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/9/2021 4:00 PM, Long Li wrote: >> @@ -1848,21 +1851,22 @@ static int storvsc_queuecommand(struct Scsi_Host >> *host, struct scsi_cmnd *scmnd) >> payload->range.len = length; >> payload->range.offset = offset_in_hvpg; >> >> + sg_count = scsi_dma_map(scmnd); >> + if (sg_count < 0) >> + return SCSI_MLQUEUE_DEVICE_BUSY; > Hi Tianyu, > > This patch (and this patch series) unconditionally adds code for dealing with DMA addresses for all VMs, including non-isolation VMs. > > Does this add performance penalty for VMs that don't require isolation? > Hi Long: scsi_dma_map() in the traditional VM just save sg->offset to sg->dma_address and no data copy because swiotlb bounce buffer code doesn't work. The data copy only takes place in the Isolation VM and swiotlb_force is set. So there is no additional overhead in the traditional VM. Thanks.