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Tue, 15 Oct 2024 15:01:47 GMT Received: from smtpav02.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 22B9858051; Tue, 15 Oct 2024 15:01:47 +0000 (GMT) Received: from smtpav02.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 376BD5805C; Tue, 15 Oct 2024 15:01:45 +0000 (GMT) Received: from wecm-9-67-37-172.wecm.ibm.com (unknown [9.67.37.172]) by smtpav02.dal12v.mail.ibm.com (Postfix) with ESMTP; Tue, 15 Oct 2024 15:01:45 +0000 (GMT) Message-ID: <8131b905c61a7baf4bd09ec4a08e1ace84d36754.camel@linux.ibm.com> Subject: Re: [PATCH v2 4/7] s390/physmem_info: query diag500(STORAGE LIMIT) to support QEMU/KVM memory devices From: Eric Farman To: Heiko Carstens , David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, virtualization@lists.linux.dev, linux-doc@vger.kernel.org, kvm@vger.kernel.org, Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Huth , Cornelia Huck , Janosch Frank , Claudio Imbrenda , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?ISO-8859-1?Q?P=E9rez?= , Andrew Morton , Jonathan Corbet , Mario Casquero Date: Tue, 15 Oct 2024 11:01:44 -0400 In-Reply-To: <20241014184339.10447-E-hca@linux.ibm.com> References: <20241014144622.876731-1-david@redhat.com> <20241014144622.876731-5-david@redhat.com> <20241014184339.10447-E-hca@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.52.4 (3.52.4-1.fc40) X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: oiDcZvE5rWbNLUCRElJ1IfzPka5qxG8w X-Proofpoint-GUID: flUxXiPfEXI7RXTEkEcHTYtcpZ7IpCgb Content-Transfer-Encoding: quoted-printable X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-15_01,2024-10-11_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 spamscore=0 lowpriorityscore=0 impostorscore=0 priorityscore=1501 bulkscore=0 clxscore=1011 malwarescore=0 phishscore=0 adultscore=0 suspectscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2409260000 definitions=main-2410150101 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A6B8B16002C X-Stat-Signature: fm1a6j53r966zn7d3pj9c49ew9kogjjh X-Rspam-User: X-HE-Tag: 1729004507-803156 X-HE-Meta: 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 /KL1UnKL moGWARj/7tGVuaXCfEN/jboxgDdY/KozQ3PcOFWTxSiyDSR4ao2VyIo1ATOpKwXaaPiOe61cLiDZWJ0KxWiIQeiECL2JeCaTSFfMQLOaHeyaJmbjZav9OvD5ZM4eoLmls1ruVLzHwokqivcEke962ETFsmvXLQKGg8W6/SK5cu1ALOtcNfsfcdiz5hNv8p8BbV1WP15sspdytZfbfWWQAMqDLWCYGVZfKkY9xbhET7yro0s3gHQal4FM5jrtP0paXnU2gNWnSAESIDdARfbp5KsGhaxjzj69/29Fq X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 2024-10-14 at 20:43 +0200, Heiko Carstens wrote: > On Mon, Oct 14, 2024 at 04:46:16PM +0200, David Hildenbrand wrote: > > To support memory devices under QEMU/KVM, such as virtio-mem, > > we have to prepare our kernel virtual address space accordingly and > > have to know the highest possible physical memory address we might see > > later: the storage limit. The good old SCLP interface is not suitable f= or > > this use case. > >=20 > > In particular, memory owned by memory devices has no relationship to > > storage increments, it is always detected using the device driver, and > > unaware OSes (no driver) must never try making use of that memory. > > Consequently this memory is located outside of the "maximum storage > > increment"-indicated memory range. > >=20 > > Let's use our new diag500 STORAGE_LIMIT subcode to query this storage > > limit that can exceed the "maximum storage increment", and use the > > existing interfaces (i.e., SCLP) to obtain information about the initial > > memory that is not owned+managed by memory devices. ...snip... > The patch below changes your code accordingly, but it is > untested. Please verify that your code still works. ...snip... > diff --git a/arch/s390/boot/physmem_info.c b/arch/s390/boot/physmem_info.c > index fb4e66e80fd8..975fc478e0e3 100644 > --- a/arch/s390/boot/physmem_info.c > +++ b/arch/s390/boot/physmem_info.c > @@ -109,10 +109,11 @@ static int diag260(void) > return 0; > } > =20 > +#define DIAG500_SC_STOR_LIMIT 4 > + > static int diag500_storage_limit(unsigned long *max_physmem_end) > { > - register unsigned long __nr asm("1") =3D 0x4; > - register unsigned long __storage_limit asm("2") =3D 0; > + unsigned long storage_limit; > unsigned long reg1, reg2; > psw_t old; > =20 > @@ -123,21 +124,24 @@ static int diag500_storage_limit(unsigned long *max= _physmem_end) > " st %[reg2],4(%[psw_pgm])\n" > " larl %[reg1],1f\n" > " stg %[reg1],8(%[psw_pgm])\n" > + " lghi 1,%[subcode]\n" > + " lghi 2,0\n" > " diag 2,4,0x500\n" > "1: mvc 0(16,%[psw_pgm]),0(%[psw_old])\n" > + " lgr %[slimit],2\n" > : [reg1] "=3D&d" (reg1), > [reg2] "=3D&a" (reg2), > - "+&d" (__storage_limit), > + [slimit] "=3Dd" (storage_limit), > "=3DQ" (get_lowcore()->program_new_psw), > "=3DQ" (old) > : [psw_old] "a" (&old), > [psw_pgm] "a" (&get_lowcore()->program_new_psw), > - "d" (__nr) > - : "memory"); > - if (!__storage_limit) > - return -EINVAL; > - /* convert inclusive end to exclusive end. */ > - *max_physmem_end =3D __storage_limit + 1; > + [subcode] "i" (DIAG500_SC_STOR_LIMIT) > + : "memory", "1", "2"); > + if (!storage_limit) > + return -EINVAL; > + /* Convert inclusive end to exclusive end */ > + *max_physmem_end =3D storage_limit + 1; > return 0; > } > =20 >=20 I like the idea of a defined constant here instead of hardcoded, but maybe = it should be placed somewhere in include/uapi so that QEMU can pick it up with update-linux-hea= ders.sh and be in sync with the kernel, instead of just an equivalent definition in [1] ? [1] https://lore.kernel.org/qemu-devel/20241008105455.2302628-8-david@redha= t.com/