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Mon, 8 Jul 2019 12:24:00 +0000 (UTC) To: Maxim Levitsky , qemu-devel@nongnu.org References: <20190703155944.9637-1-mlevitsk@redhat.com> <20190703155944.9637-2-mlevitsk@redhat.com> From: Max Reitz Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <5d32c846-1ff6-ec99-af20-8e7a794c4fe2@redhat.com> Date: Mon, 8 Jul 2019 14:23:58 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="USCwwg2j1GX8g46N9jXoW4sJJc16TrjzP" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 08 Jul 2019 12:24:11 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v3 1/6] block/nvme: don't touch the completion entries X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , Paolo Bonzini , John Snow , qemu-block@nongnu.org, Kevin Wolf Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --USCwwg2j1GX8g46N9jXoW4sJJc16TrjzP Content-Type: multipart/mixed; boundary="gdQUBiS15iMXSaUEvDyHWdGaa1XfG5TXb"; protected-headers="v1" From: Max Reitz To: Maxim Levitsky , qemu-devel@nongnu.org Cc: Paolo Bonzini , Fam Zheng , Kevin Wolf , John Snow , qemu-block@nongnu.org Message-ID: <5d32c846-1ff6-ec99-af20-8e7a794c4fe2@redhat.com> Subject: Re: [PATCH v3 1/6] block/nvme: don't touch the completion entries References: <20190703155944.9637-1-mlevitsk@redhat.com> <20190703155944.9637-2-mlevitsk@redhat.com> In-Reply-To: --gdQUBiS15iMXSaUEvDyHWdGaa1XfG5TXb Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 07.07.19 10:43, Maxim Levitsky wrote: > On Fri, 2019-07-05 at 13:03 +0200, Max Reitz wrote: >> On 03.07.19 17:59, Maxim Levitsky wrote: >>> Completion entries are meant to be only read by the host and written = by the device. >>> The driver is supposed to scan the completions from the last point wh= ere it left, >>> and until it sees a completion with non flipped phase bit. >> >> (Disclaimer: This is the first time I read the nvme driver, or really >> something in the nvme spec.) >> >> Well, no, completion entries are also meant to be initialized by the >> host. To me it looks like this is the place where that happens: >> Everything that has been processed by the device is immediately being >> re-initialized. >> >> Maybe we shouldn=E2=80=99t do that here but in nvme_submit_command(). = But >> currently we don=E2=80=99t, and I don=E2=80=99t see any other place wh= ere we currently >> initialize the CQ entries. >=20 > Hi! > I couldn't find any place in the spec that says that completion entries= should be initialized. > It is probably wise to initialize that area to 0 on driver initializati= on, but nothing beyond that. Ah, you=E2=80=99re right, I misread. I didn=E2=80=99t pay as much attent= ion to the =E2=80=9C...prior to setting CC.EN to =E2=80=981=E2=80=99=E2=80=9D as I s= hould have. Yep, and that is done in nvme_init_queue(). OK, I cease my wrongful protest: Reviewed-by: Max Reitz > In particular that is what the kernel nvme driver does.=20 > Other that allocating a zeroed memory (and even that I am not sure it d= oes),=20 > it doesn't write to the completion entrie --gdQUBiS15iMXSaUEvDyHWdGaa1XfG5TXb-- --USCwwg2j1GX8g46N9jXoW4sJJc16TrjzP Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl0jNd4ACgkQ9AfbAGHV z0DN5gf/UG3C0NhsOGgY68EqJEOnUfHBdD2zTYukESt4vb+GcXBuHoSP+GpwcnKO qeOlBOffwCmpmyOrHr6derj6J9jLn2G5Pj6yz9x/01z3A0KzBRvf/2hEpBxw5Biy Ik+4AvXYh+ZeYY9fltKOg0T241T7EkWrGKNoDoSktQrl/DMVFKt1vqNJTEydXYtF KQbNI/7rnBppMKPj+HnLTxxd4yezYe9h48tctGhTy/tFU51yjlLl7o4HqabpISns 8OhHroBBj0JBv2b2DHwA4aeaVMsy41vpRMSLEspxd0mn7wyjaBENEiPrzou9lbCj vRUv9Cim/2A4QIMuyoIaf8qkvF44fQ== =L0W2 -----END PGP SIGNATURE----- --USCwwg2j1GX8g46N9jXoW4sJJc16TrjzP--