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Message-ID: <7d783993-1ef5-e1ed-591c-c87a9d879782@intel.com>
Date:   Mon, 18 Sep 2023 15:16:48 +0800
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Subject: Re: [PATCH v6 01/25] x86/fpu/xstate: Manually check and add
 XFEATURE_CET_USER xstate bit
To:     "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     "peterz@infradead.org" <peterz@infradead.org>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        "Gao, Chao" <chao.gao@intel.com>,
        "john.allen@amd.com" <john.allen@amd.com>
References: <20230914063325.85503-1-weijiang.yang@intel.com>
 <20230914063325.85503-2-weijiang.yang@intel.com>
 <868ea527d82f8b9ab7360663db0ef42e6900dc87.camel@intel.com>
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 <c91f6e5885b8d052b0a1d96d0ccc5a479d9f2b69.camel@intel.com>
Content-Language: en-US
From:   "Yang, Weijiang" <weijiang.yang@intel.com>
In-Reply-To: <c91f6e5885b8d052b0a1d96d0ccc5a479d9f2b69.camel@intel.com>
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On 9/16/2023 12:35 AM, Edgecombe, Rick P wrote:
> On Fri, 2023-09-15 at 10:32 +0800, Yang, Weijiang wrote:
>>> Also, this doesn't discuss the real main reason for this patch, and
>>> that is that KVM will soon use the xfeature for user ibt, and so
>>> there
>>> will now be a reason to have XFEATURE_CET_USER depend on IBT.
>> This is one justification for Linux OS, another reason is there's
>> non-Linux
>> OS which is using the user IBT feature.  I should make the reasons
>> clearer
>> in changelog, thanks for pointing it out!
> The point I was trying to make was today (before this series) nothing
> on the system can use user IBT. Not the host, and not in any guest
> because KVM doesn't support it. So the added xfeature dependency on IBT
> was not previously needed. It is being added only for KVM CET support
> (which, yes, may run on guests with non-standard CPUID).

Agree, I'll highlight this in changelog, thanks!