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b=h2y5lJl1SM2LSuMqP3w2LP6USGSOeShzPf8h4y/SmVp3eWLWGQdbv5N5HzfLFq3uX3v4VQCT4/d6RnGqYYjdQ2fdXp/a1COq6HjjMBrUqCIGt1JeWa95ACwL8CWXlfgT9uxB2sm2qVY5Hiqk4FcSKCCeexrrWb/zZzn39R1lPbw= Received: from MWHPR21MB1593.namprd21.prod.outlook.com (2603:10b6:301:7c::11) by SN6PR2101MB1855.namprd21.prod.outlook.com (2603:10b6:805:10::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4801.6; Thu, 9 Dec 2021 19:54:26 +0000 Received: from MWHPR21MB1593.namprd21.prod.outlook.com ([fe80::e9ea:fc3b:df77:af3e]) by MWHPR21MB1593.namprd21.prod.outlook.com ([fe80::e9ea:fc3b:df77:af3e%8]) with mapi id 15.20.4801.007; Thu, 9 Dec 2021 19:54:26 +0000 From: "Michael Kelley (LINUX)" To: Haiyang Zhang , Tianyu Lan , KY Srinivasan , 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" 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" Subject: RE: [PATCH V6 5/5] net: netvsc: Add Isolation VM support for netvsc driver Thread-Topic: [PATCH V6 5/5] net: netvsc: Add Isolation VM support for netvsc driver Thread-Index: AQHX6z/p4N8f/0zLXkWT82yvkJZgZ6wpCdOAgAGKX2A= Date: Thu, 9 Dec 2021 19:54:25 +0000 Message-ID: References: <20211207075602.2452-1-ltykernel@gmail.com> <20211207075602.2452-6-ltykernel@gmail.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ActionId=8f2b756c-5454-4ec4-ac2e-44d9b23f1862;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ContentBits=0;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=true;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Method=Standard;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Name=Internal;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SetDate=2021-12-08T20:06:08Z;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SiteId=72f988bf-86f1-41af-91ab-2d7cd011db47; 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x-ms-exchange-antispam-messagedata-chunkcount: 1 x-ms-exchange-antispam-messagedata-0: 4IpGc1OhfBdKKqxnSdVHZ28drWU2IzchduNAjcc/J5wUvTz48FgxnjzlMJVzb6KtIcYWPxwyl6Ok9N00/DAK8/TCfjjbQkgarowUex+wgYMEktEAlXMffnBbO20XPTz+LbKbqobIV1uK5JWQgzHUj5PkXCJ1vEnGJG3iBgx1+YmsbkgaCxa27EUrKnRpPn+xH75dVKll5XOWwaIycRHyPAp5SkbE8fdTbXoHJB5NeYXk5olNfFiRtYKgCu+KMmDVuZyhJXresCOI8fSqNsHe3CIQO/ni+HWa9Xku5+AxfMZMDkrrwEbtpPt0b5XaiBDN0Zn4yojPCCkMzThhMi/YZ+VjC8q9puc7YG4UgA4fITsDBigauNxGIStXqOL625y9/c072MUAXxkw4bOhj3N2HYLO08i5wp+CGBGK2jVtmupDycl5637/MdZM9RAWl6qrIhxCX89BKME7+nkA+qcMT5IvSbz4EL5z2c1I/zQ3lR0xJhBX2q59axe1t/CBKPgP Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: MWHPR21MB1593.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3532b909-8c81-40c9-37db-08d9bb4db440 X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Dec 2021 19:54:25.8519 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: GIMQ+6UyJhE6eyTFBlqtGCgXVSWCbcshMc4F2DixgP0wOOkGjwIQBIz4e+87S+CsF/bpsOV1zqmlk83x+Ao0u6krNJQbWt0BBtVdKGfxm4o= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR2101MB1855 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Haiyang Zhang Sent: Wednesday, December 8, 2= 021 12:14 PM > > From: Tianyu Lan > > Sent: Tuesday, December 7, 2021 2:56 AM [snip] > > static inline int netvsc_send_pkt( > > struct hv_device *device, > > struct hv_netvsc_packet *packet, > > @@ -986,14 +1105,24 @@ static inline int netvsc_send_pkt( > > > > trace_nvsp_send_pkt(ndev, out_channel, rpkt); > > > > + packet->dma_range =3D NULL; > > if (packet->page_buf_cnt) { > > if (packet->cp_partial) > > pb +=3D packet->rmsg_pgcnt; > > > > + ret =3D netvsc_dma_map(ndev_ctx->device_ctx, packet, pb); > > + if (ret) { > > + ret =3D -EAGAIN; > > + goto exit; > > + } >=20 > Returning EAGAIN will let the upper network layer busy retry, > which may make things worse. > I suggest to return ENOSPC here like another place in this > function, which will just drop the packet, and let the network > protocol/app layer decide how to recover. >=20 > Thanks, > - Haiyang I made the original suggestion to return -EAGAIN here. A DMA mapping failure should occur only if swiotlb bounce buffer space is unavailable, which is a transient condition. The existing code already stops the queue and returns -EAGAIN when the ring buffer is full, which is also a transient condition. My sense is that the two conditions should be handled the same way. Or is there a reason why a ring buffer full condition should stop the queue and retry, while a mapping failure should drop the packet? Michael