Received-SPF: pass (google.com: domain of linux-kernel+bounces-169419-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Message-ID: <b0ccf68d-38e0-4522-8a54-974d5a711923@intel.com>
Date: Mon, 6 May 2024 15:30:59 +0800
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v10 13/27] KVM: x86: Refresh CPUID on write to guest
 MSR_IA32_XSS
To: Sean Christopherson <seanjc@google.com>
CC: <pbonzini@redhat.com>, <dave.hansen@intel.com>, <x86@kernel.org>,
	<kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<peterz@infradead.org>, <chao.gao@intel.com>, <rick.p.edgecombe@intel.com>,
	<mlevitsk@redhat.com>, <john.allen@amd.com>, Zhang Yi Z
	<yi.z.zhang@linux.intel.com>
References: <20240219074733.122080-1-weijiang.yang@intel.com>
 <20240219074733.122080-14-weijiang.yang@intel.com>
 <ZjKphDaJ5Bq-jTVx@google.com>
Content-Language: en-US
From: "Yang, Weijiang" <weijiang.yang@intel.com>
In-Reply-To: <ZjKphDaJ5Bq-jTVx@google.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?RjhKcStmTURpaDYrT2t6Mnk0amNjc1lUYVhsWmVKb0VuNWhZLzZWdUVmQng1?=
 =?utf-8?B?QittbTl5Uk9Pbld0QXNjL3BoZm9RVk0vVGZyYlZweDhFc0VHY1N5VHk0QmU0?=
 =?utf-8?B?VE1IZVpMUGUweFNPWnYxN1pCenFkaVBDd2wvV3Q2OG5rc1NDVytyMVRKR3FS?=
 =?utf-8?B?aUE1bmpFdU5iWXEvclU4YzNMa1V2WGYvVDFFNVJLMEtxSjVLa1BMVmdXZ3kz?=
 =?utf-8?B?YkNjRWdKMHN3Qm9aNzlQY1JtQWIvS0J2aGpCQ2Nrd2RPc2dPQVlXbkVuQlJD?=
 =?utf-8?B?N09DK0pYRkErVENRQkFGa1hheUdBUm8wSTRISGROVXZDNjFFVmJoT01HRHFp?=
 =?utf-8?B?OXJwWHRaQXhzTmZiUnVXZzFNQTE0YlUreGV6Nmpsb3pZYnFlS21mWGRkVjRX?=
 =?utf-8?B?TXZuckFaRHNla3REZlNVN3AxU0RrTE9uQWNQRnpHMWVEVjNVcnV6NTFLNWR6?=
 =?utf-8?B?RXR3dUFoYjNCNjRMMUYvaHo0dGtDcm43c20wVlVzQlV5YVhkWjN0UERWVXdZ?=
 =?utf-8?B?bWQrbGNrakdXYjRjajRsR0xEcDF6Rld5ckg2eXpQT0NvMjVacGtQY1p6Z3pS?=
 =?utf-8?B?aldxcHFJSlE5NmNucXJWMWtXM0laNDlXV2ZWRDJqZS9NcVNyd0lvTzFmTHZI?=
 =?utf-8?B?eHhTQ01UVTFtNFpqZEJzNUNDNllSSE93KzZhRnVDYW1oVFJMWkorWmp6QTlv?=
 =?utf-8?B?Tjlwa2VMb1UzcDBzVXZ3WlBMQ0E4am5TNUhJaXRSak5NN1ZSUFBScy9RTXFY?=
 =?utf-8?B?czErYSs0OUI1Vmx4N3BuUmF4OEZRNmlMOTBaTTArZFpxTVhzV2JHdnVKVnBE?=
 =?utf-8?B?QmNtZ0JZS2d0VURKY1MxU1JTbDJpaVhEUTlVMm9sLzJDOXUyTC9nb2VVWUVy?=
 =?utf-8?B?S1B5OCtaQVVEcjdvZDJKVVBKbjNtb1lDaENvMi9Fd1EwWDNjcTFrMmZ0VUIw?=
 =?utf-8?B?VXVNM2RFR2g3cFlhMTFaR2l4TDBNQUJMcERNNDF2VFNEbmdhVllURCtyMU0x?=
 =?utf-8?B?bU0wekI4dTlENFhzWnd3U0thQ2lQWEtHVTBoT0RmcTJtWEI1SVdteDVMK3BZ?=
 =?utf-8?B?ZG9tOFF6TjEzNWt2djNsN1BHTlp0K3JnS0NveUw3UUJPdVg4cCtBRkVTUjRT?=
 =?utf-8?B?ODZYV2d2M2wySFZ3dXRKWmhRY0k2YWpwa3hVRU1aNkc3UzdVcjZNV3dDYkdp?=
 =?utf-8?B?bXBQbzAwMmZRN2s2Q0t5N0RYcXlmcVpXbWVqaitrUHhSTzUzNERMRVNRc09Q?=
 =?utf-8?B?SDVEcitWTEd0a1VsdFFBZ1lySWFIZXhzUjJHSjNBLzhWNWxndGhXSEJpOWZa?=
 =?utf-8?B?eTFidVEvY1BFSnRDa1Z0Q21FVmlHTmZVQmYzYTkvM0Y1RGlFS1ZtUzZ4cTdw?=
 =?utf-8?B?UjBCYkY1Wk94SmZhdDFPNHdsV0dRRVdTMnBvQU9qSitvaC84ejUxRlQvTXBX?=
 =?utf-8?B?YjNJbmxGL2V0azc0VGtMZEM0cVQ4Wit3d2l1UFpGKzIxUUJUbDAvUHA3MUtk?=
 =?utf-8?B?ODZnU2l0U1kxMS9hdGxEQldnalhPNHhLUTk5TkVPRUxlZ005MTFSV3JNQnVE?=
 =?utf-8?B?VGVJaFBRQkthUnlxTTNsb1RWZHhvcE9uV1BHS3QzdUZhbmtGL0hSV21GSnlK?=
 =?utf-8?B?NEtSNTRhemJ3QmtZVE9ZVU9Mc0xFMFRBYTMyNHVMbGxDY2IvWm1UVXNYaC90?=
 =?utf-8?B?TmpXdTM0TUVidlJ0ODY3OWRReU5wMzJiR2s0VGQ4QytqNFJ6aVpBNlk2REoy?=
 =?utf-8?B?cDBkYnhKU3l3dlB6dXo4YXRKZ3Y1L3h5RHJ4ZFR6dmRBbWppYU9EODZoRDBE?=
 =?utf-8?B?djRXRmkrNS9jT3JDRE9CQTJLdFkwT1NiRTNxSnZFZFFEWnFVdDVlM2t0VFQr?=
 =?utf-8?B?ZTVqbWJRQUZ4R2plTUpiTGZ6WjNLNjNrT1YwNVd5Q2lvVEU5THNXUDRzQ1Fw?=
 =?utf-8?B?aE1rRnJGa0JHTkR6aW96bTUxeFd5M2Q0WTZZbzVWS0VXRzNCNno4WEJXYW5k?=
 =?utf-8?B?bFR1SktGZWVEVmxpazNPZGlDWDhGQk8rMGxuUXNHYlZzbnF5WXY4NFMrU3hw?=
 =?utf-8?B?bnVOd1B1YUVPTS8vckRpaTNpa2N5azBqZDcvb1ZZWE9lcTdiTlZjNkJwQTdO?=
 =?utf-8?B?SWVRNkZXQTYzMVpmWUNtN29ZbERtdWhlckNJVW9QOFg2V0xKcklYOEFLb3FY?=
 =?utf-8?B?b3c9PQ==?=
X-MS-Exchange-CrossTenant-Network-Message-Id: f5badbc9-0dc2-49db-156e-08dc6d9e8bf1
X-MS-Exchange-CrossTenant-AuthSource: PH0PR11MB4965.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2024 07:31:30.3623
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: UpHBiIDxFHek88h/Hx0wtDA2qYtAZOmpAm3rppL2SCvs6iaHyM4WAe0qtHq7O3p3pD4jLbwxe6id2w6QuSfO1g==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB4790
X-OriginatorOrg: intel.com

On 5/2/2024 4:43 AM, Sean Christopherson wrote:
> On Sun, Feb 18, 2024, Yang Weijiang wrote:
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 9eb5c8dbd4fb..b502d68a2576 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -3926,16 +3926,23 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>   		}
>>   		break;
>>   	case MSR_IA32_XSS:
>> -		if (!msr_info->host_initiated &&
>> -		    !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
>> +		/*
>> +		 * If KVM reported support of XSS MSR, even guest CPUID doesn't
>> +		 * support XSAVES, still allow userspace to set default value(0)
>> +		 * to this MSR.
>> +		 */
>> +		if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES) &&
>> +		    !(msr_info->host_initiated && data == 0))
> With my proposed MSR access cleanup[*], I think (hope?) this simply becomes:
>
> 		if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
> 			return KVM_MSR_RET_UNSUPPORTED;
>
> with no comment needed as the "host && !data" case is handled in common code.

Right, I'll change this part after the cleanup series is merged. Thanks!

>
> [*] https://lore.kernel.org/all/20240425181422.3250947-1-seanjc@google.com