Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <3ee385a8-b4f4-0124-42e1-0f5c2a393456@amd.com>
Date:   Mon, 7 Nov 2022 16:40:18 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.2.2
Content-Language: en-US
To:     David Laight <David.Laight@ACULAB.COM>,
        'Borislav Petkov' <bp@alien8.de>
Cc:     "x86@kernel.org" <x86@kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Joao Martins <joao.m.martins@oracle.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Tony Luck <tony.luck@intel.com>,
        Babu Moger <Babu.Moger@amd.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20221104213651.141057-1-kim.phillips@amd.com>
 <20221104213651.141057-3-kim.phillips@amd.com> <Y2WJjdY3wwQl9/q9@zn.tnic>
 <49e01e4d819a4e3aa1ef13da6bc654e4@AcuMS.aculab.com>
From:   Kim Phillips <kim.phillips@amd.com>
Subject: Re: [PATCH 2/3] x86/speculation: Support Automatic IBRS
In-Reply-To: <49e01e4d819a4e3aa1ef13da6bc654e4@AcuMS.aculab.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?L050L3JjajM5eEhuRndOSVFpY0pqQnJnckFYcnlldHFhVkEyOWZzYlFUczBa?=
 =?utf-8?B?UU4rRE93ZDFxRitaV0kwMTdKVUpaMkVaRUVLWW9VSEdmdDlVaXMxb3RDQlM1?=
 =?utf-8?B?a21GZlFCVG5vZFBrTGZ4NDBvYkFkK0twS05KWUh0SXJDU09GZkZnNUFSWUdm?=
 =?utf-8?B?MWdRMDBKZWtueWVRa1Z5Yk4zVWFNOWFJTXRGM0xCWmlxWDV0QVlic0pnRi82?=
 =?utf-8?B?Ynppc2ZWa0ZtRkx2SVprc1lPcXBUQ1BHK3pINTdKUXZxQStuZm1YcDBHY29I?=
 =?utf-8?B?eEx5UUVycFVSQ2VVUzR6eDBBQzJLTlo5ZlZJdzZDSXdJZ0ZFd2JxNjFmUUVi?=
 =?utf-8?B?bFVTdlc4UDJZZzdxcGpuR0RkaXd3V0UyVVRxTGwxdHVXZ3BZczE5S1ZmWnNC?=
 =?utf-8?B?S0F2UWJ6VEhPYkRnL0RYUGRCb3NLWUZMNFRleCszd1ozS1VPL2JYVXN3eDc4?=
 =?utf-8?B?WVJ5TGU1anNFR1lqMXA5a3JTVHcyc05zTnlMWFp6c2x5clNuUTN4NWtjZlVJ?=
 =?utf-8?B?TG9vN3dTV1ZtYnU2M1JQaUlVSkpLQWZqTWhYYVltV041b0JWeUN4bnRMRlhS?=
 =?utf-8?B?K1BKaG9MaVZGc3lYOGdaemtmNUgwQUpIMUM2dEhYZElCd0w2cG9YOW9YWjZ5?=
 =?utf-8?B?Z08zUWlQbWRXbHM2OWZubXVvTnBXMWsvVXRwazBsSERHVG4rYU1ZVDBuakFC?=
 =?utf-8?B?eFlKWGFZVXQ4aWhRaFFMR1FTZitkNW1Mbnh6RE5oWFF2OW9NU0xSc1Q2cDZw?=
 =?utf-8?B?VWxnSTJPQW5iaE5rdSs0TktJMTNxUGlYck9Qc2ZSS1RqOTRBUHd2Wmd0b2VS?=
 =?utf-8?B?R243UytQVUtnWEp3S3BVTmJCL09DQ0dEZkI0SCs3L1AxM3g1MjNzTEQ1YWlJ?=
 =?utf-8?B?MzlYcWRVaFQ1U1N5QlU4MmkraFdmMWx4c21qajFDS2gxSmJxdXVRY1I1WGNl?=
 =?utf-8?B?dGpxK293R2d0cnpOVm54SEZ4dTZmaFNLQnhmZGNvL01JNzlHdkFha1VVVmtL?=
 =?utf-8?B?UTY4Yzc4QXY0N05HUDg4OHgrYXJLMnc5T2R4TVE1T0xCdmczdFZla0ZpcTdI?=
 =?utf-8?B?K3E5WEZJMDdITWZRa2pxTVhrUDVZcytjM1JLTkh5dVBmaFBIT0t5N0FxWW05?=
 =?utf-8?B?M2RNOTNMVWM4dkY3WjlRRWtwWi8yam5lVm9ZQjVUL1k2R1dSYVhEQ29xNjAz?=
 =?utf-8?B?SlNNeFlOUk8xMnp1RjgvQ1E2dzh2UDFzdHNWeWJyVHpJM2NpNk92WFVpTVFo?=
 =?utf-8?B?d0tYSWVQRndHTzVmT0hTdDRQM2hybEg5WEtaNTB0U0dCdllxc09WMlo0YUNh?=
 =?utf-8?B?cXVzcWZ2aCtRZFlYUEJhL3IrYThORnRpeWtYWkIvQWphNlFyOUNYM0wxTzRi?=
 =?utf-8?B?Z2c5eW5lWDkreFNaODJoWFFPU3N4QnJUeDVDZVJlU0lZdjhrcGVxdnJrbFJL?=
 =?utf-8?B?dDg5ei9CV2tmbjNmUWs3VEh4dFZ2UjEzMUZZaUlUWGZnbHYvMzJyS3p3ODBM?=
 =?utf-8?B?bnlyaW1vWGl4dzBaWDJrcFJoZC9Gakd0MEJpcjJ6YzVPRG5oeml0anFGY3Z3?=
 =?utf-8?B?NDRFcjJnZG80dHBtR2ZTRC9OTDlMQkd5b0hSV3ZLcUVtSk1GYktOczBJaktU?=
 =?utf-8?B?cWVsdFJYWVM4UlhuNDBqS3ZqU1JGcHAwcUhFcVAweXJVWXp6M0ZselJrV003?=
 =?utf-8?B?eHdRWmxVMk5tcFU4ZEtPckJpSWhNcENvbWJhcm9vaFIyZGJyTUdhV051WTg5?=
 =?utf-8?B?M0lMdDNFM1dEMkY4bDBMV09uaS9LL08wTzVSMk1WRVMwdEpmakVIVGVTRk5Q?=
 =?utf-8?B?TzNkMmVENmJpclVYL2ZxVWJtamRTcmZvOTlTeG1xc3cxMlgwbXZPTG1vZmJl?=
 =?utf-8?B?aExvbk5UeG8xOFNHUUQ3RTNFUVdtWU1yRFZjZXRwOHpXK2hYQUJiQTZLT242?=
 =?utf-8?B?bEUrYlBlMyt2RG9QR3Z5VklxMVExMVJXZTMxSFFLdVNtdXhzdTNOYWVlK2ZR?=
 =?utf-8?B?cndYSTk5ZVlpakdNWmtNZ3hRNU53b2MrQWZlM2w1MVpNN0lObTYxQS9tNFAv?=
 =?utf-8?B?UytFekplbkh0c0JEOXJmVmdxeGlSRHA5THdHYjQ4VllyM2lqMEY1RW5saEZW?=
 =?utf-8?Q?sWTU8Q7KS/SXo7SiF3rNcbzmi?=
X-OriginatorOrg: amd.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 7d190b40-13f8-409a-6872-08dac1110d51
X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB6263.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Nov 2022 22:40:20.9327
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: /bz9D8HGU8tRqLq3FAIqduVWallu+/Xbh96KT93UvFFISijQHp6lvIJ9AMLOkYJ+pfJApOu6Jt/ZbxxBnKPolg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR12MB5347
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,
        RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_PASS autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 11/5/22 6:39 AM, David Laight wrote:
> From: Borislav Petkov
>> Sent: 04 November 2022 21:52
>>
>> On Fri, Nov 04, 2022 at 04:36:50PM -0500, Kim Phillips wrote:
>>>   - Allow for spectre_v2=autoibrs in the kernel command line,
>>>     reverting to auto-selection if the feature isn't available.
>>
>> Why?
>>
>> What the whole logic here should do is enable autoibrs when detected
>> automatically, without the need for the user to even select it as it is
>> the superior mitigation.
> 
> The only useful option is to allow a different option be
> selected for code testing.
> So maybe you want an option for completeness - for when
> an 'even better' option is available.

This is true.

Kim