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Fri, 21 Jan 2022 13:50:25 +0000 (GMT) Message-ID: <1bd19f35-aaa1-1668-60ec-14b999b8e4e2@linux.ibm.com> Date: Fri, 21 Jan 2022 14:50:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [RFC PATCH v1 04/10] KVM: s390: selftests: Test TEST PROTECTION emulation Content-Language: en-US To: Claudio Imbrenda Cc: Janosch Frank , Paolo Bonzini , Christian Borntraeger , David Hildenbrand , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <20220118095210.1651483-1-scgl@linux.ibm.com> <20220118095210.1651483-5-scgl@linux.ibm.com> <06422388-8389-6954-00c7-7b582b4cf1bb@linux.ibm.com> <20220121132801.12ea572f@p-imbrenda> From: Janis Schoetterl-Glausch In-Reply-To: <20220121132801.12ea572f@p-imbrenda> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: jR3cGsM2MG5NDoDjLwFFguK8WhEyXniz X-Proofpoint-ORIG-GUID: u3sLOEDWebyD0b2qnhKMRClvDgZSoRrx 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 mlxscore=0 phishscore=0 spamscore=0 clxscore=1015 malwarescore=0 bulkscore=0 mlxlogscore=999 suspectscore=0 impostorscore=0 lowpriorityscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2201110000 definitions=main-2201210091 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/21/22 13:28, Claudio Imbrenda wrote: > On Fri, 21 Jan 2022 12:03:20 +0100 > Janis Schoetterl-Glausch wrote: > > [...] > >>>> + >>>> +static int set_storage_key(void *addr, uint8_t key) >>>> +{ >>>> +    int not_mapped = 0; >>>> + >>> >>> Maybe add a short comment: >>> Check if address is mapped via lra and set the storage key if it is. >>> >>>> +    asm volatile ( >>>> +               "lra    %[addr], 0(0,%[addr])\n" >>>> +        "    jz    0f\n" >>>> +        "    llill    %[not_mapped],1\n" >>>> +        "    j    1f\n" >>>> +        "0:    sske    %[key], %[addr]\n" >>>> +        "1:" >>>> +        : [addr] "+&a" (addr), [not_mapped] "+r" (not_mapped) >>> >>> Shouldn't this be a "=r" instead of a "+r" for not_mapped? >> >> I don't think so. We only write to it on one code path and the compiler mustn't conclude >> that it can remove the = 0 assignment because the value gets overwritten anyway. >> >> Initially I tried to implement the function like this: >> >> 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; >> } >> >> Which I think is nicer, but the compiler just optimized that completely away. >> I have no clue why it (thinks it) is allowed to do that. >> >>> >>>> +        : [key] "r" (key) >>>> +        : "cc" >>>> +    ); >>>> +    return -not_mapped; >>>> +} >>>> + >>>> +enum permission { >>>> +    READ_WRITE = 0, >>>> +    READ = 1, >>>> +    NONE = 2, >>>> +    UNAVAILABLE = 3, >>> >>> TRANSLATION_NA ? >>> I'm not completely happy with these names but I've yet to come up with a better naming scheme here. >> >> Mentioning translation is a good idea. Don't think there is any harm in using >> 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 Fine with me. I'll rename NONE to RW_PROTECTED. NONE is too nondescript. > >>> >>>> +}; >>>> + >>>> +static enum permission test_protection(void *addr, uint8_t key) >>>> +{ >>>> +    uint64_t mask; >>>> + >>>> +    asm volatile ( >>>> +               "tprot    %[addr], 0(%[key])\n" >>>> +        "    ipm    %[mask]\n" >>>> +        : [mask] "=r" (mask) >>>> +        : [addr] "Q" (*(char *)addr), >>>> +          [key] "a" (key) >>>> +        : "cc" >>>> +    ); >>>> + >>>> +    return (enum permission)mask >> 28; >>> >>> You could replace the shift with the "srl" that we normally do. >> >> I prefer keeping the asm as small as possible, C is just so much easier to 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); That is better indeed. 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