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Fri, 21 Jan 2022 12:28:03 +0000 (GMT) Received: from p-imbrenda (unknown [9.145.3.16]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 21 Jan 2022 12:28:03 +0000 (GMT) Date: Fri, 21 Jan 2022 13:28:01 +0100 From: Claudio Imbrenda To: Janis Schoetterl-Glausch Cc: Janosch Frank , Paolo Bonzini , Christian Borntraeger , David Hildenbrand , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [RFC PATCH v1 04/10] KVM: s390: selftests: Test TEST PROTECTION emulation Message-ID: <20220121132801.12ea572f@p-imbrenda> In-Reply-To: <06422388-8389-6954-00c7-7b582b4cf1bb@linux.ibm.com> References: <20220118095210.1651483-1-scgl@linux.ibm.com> <20220118095210.1651483-5-scgl@linux.ibm.com> <06422388-8389-6954-00c7-7b582b4cf1bb@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: wm9f8tVj-C_33B3hqwjpUM5nHuOE1fhx X-Proofpoint-GUID: AfvP6VQSoO0oDHQ0emhGL6vcHt_kkM99 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.816,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2022-01-21_06,2022-01-21_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 lowpriorityscore=0 bulkscore=0 mlxlogscore=999 mlxscore=0 impostorscore=0 phishscore=0 adultscore=0 clxscore=1011 spamscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2201110000 definitions=main-2201210082 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 21 Jan 2022 12:03:20 +0100 Janis Schoetterl-Glausch wrote: [...] > >> + > >> +static int set_storage_key(void *addr, uint8_t key) > >> +{ > >> +=C2=A0=C2=A0=C2=A0 int not_mapped =3D 0; > >> + =20 > >=20 > > Maybe add a short comment: > > Check if address is mapped via lra and set the storage key if it is. > > =20 > >> +=C2=A0=C2=A0=C2=A0 asm volatile ( > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 "lra=C2=A0=C2=A0=C2=A0 %[addr], 0(0,%[addr])\n" > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "=C2=A0=C2=A0=C2=A0 jz=C2= =A0=C2=A0=C2=A0 0f\n" > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "=C2=A0=C2=A0=C2=A0 llill= =C2=A0=C2=A0=C2=A0 %[not_mapped],1\n" > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "=C2=A0=C2=A0=C2=A0 j=C2= =A0=C2=A0=C2=A0 1f\n" > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "0:=C2=A0=C2=A0=C2=A0 sske= =C2=A0=C2=A0=C2=A0 %[key], %[addr]\n" > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "1:" > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : [addr] "+&a" (addr), [no= t_mapped] "+r" (not_mapped) =20 > >=20 > > Shouldn't this be a "=3Dr" instead of a "+r" for not_mapped? =20 >=20 > I don't think so. We only write to it on one code path and the compiler m= ustn't conclude > that it can remove the =3D 0 assignment because the value gets overwritte= n anyway. >=20 > Initially I tried to implement the function like this: >=20 > static int set_storage_key(void *addr, uint8_t key) > { > asm goto ("lra %[addr], 0(0,%[addr])\n\t" > "jnz %l[not_mapped]\n\t" > "sske %[key], %[addr]\n" > : [addr] "+&a" (addr) > : [key] "r" (key) > : "cc", "memory" > : not_mapped > ); > return 0; > not_mapped: > return -1; > } >=20 > Which I think is nicer, but the compiler just optimized that completely a= way. > I have no clue why it (thinks it) is allowed to do that. >=20 > > =20 > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : [key] "r" (key) > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : "cc" > >> +=C2=A0=C2=A0=C2=A0 ); > >> +=C2=A0=C2=A0=C2=A0 return -not_mapped; > >> +} > >> + > >> +enum permission { > >> +=C2=A0=C2=A0=C2=A0 READ_WRITE =3D 0, > >> +=C2=A0=C2=A0=C2=A0 READ =3D 1, > >> +=C2=A0=C2=A0=C2=A0 NONE =3D 2, > >> +=C2=A0=C2=A0=C2=A0 UNAVAILABLE =3D 3, =20 > >=20 > > TRANSLATION_NA ? > > I'm not completely happy with these names but I've yet to come up with = a better naming scheme here. =20 >=20 > Mentioning translation is a good idea. Don't think there is any harm in u= sing > TRANSLATION_NOT_AVAILABLE or TRANSLATION_UNAVAILABLE. it's too long, it actually makes the code harder to read when used maybe consider something like TRANSL_UNAVAIL as well > > =20 > >> +}; > >> + > >> +static enum permission test_protection(void *addr, uint8_t key) > >> +{ > >> +=C2=A0=C2=A0=C2=A0 uint64_t mask; > >> + > >> +=C2=A0=C2=A0=C2=A0 asm volatile ( > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 "tprot=C2=A0=C2=A0=C2=A0 %[addr], 0(%[key])\n" > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "=C2=A0=C2=A0=C2=A0 ipm=C2= =A0=C2=A0=C2=A0 %[mask]\n" > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : [mask] "=3Dr" (mask) > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : [addr] "Q" (*(char *)add= r), > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 [key] "a" (key) > >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : "cc" > >> +=C2=A0=C2=A0=C2=A0 ); > >> + > >> +=C2=A0=C2=A0=C2=A0 return (enum permission)mask >> 28; =20 > >=20 > > You could replace the shift with the "srl" that we normally do. =20 >=20 > I prefer keeping the asm as small as possible, C is just so much easier t= o understand. we use srl everywhere, but I agree that explicitly using C makes it less obscure. and in the end the compiler should generate the same instructions anyway. my only comment about the above code is that you are casting the uint64_t to enum permission _and then_ shifting. _technically_ it should still work (enums are just ints), but I think it would look cleaner if you write return (enum permission)(mask >> 28); >=20 > [...] >=20 > > It's __really__ hard to understand this since the state is changed both= by the guest and host. Please add comments to this and maybe also add some= to the test struct explaining why you expect the results for each test. > > =20 >=20 > I think I'll concentrate the comments at the tests array so we have one l= ocation > that lays out the complete logic and then one only has to check if the gu= est > and host match up with that, respectively, instead of having to model the= ir interaction > in ones head. >=20 > I'll incorporate your other feedback, too. >=20 > Thanks!