Message-ID: <2e2ab02c-b324-e136-924a-0376040163a8@redhat.com>
Date:   Wed, 17 Nov 2021 08:31:17 +0100
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Subject: Re: Thoughts of AMX KVM support based on latest kernel
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To:     "Nakajima, Jun" <jun.nakajima@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>
Cc:     "Liu, Jing2" <jing2.liu@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Jing Liu <jing2.liu@linux.intel.com>,
        "seanjc@google.com" <seanjc@google.com>,
        "Cooper, Andrew" <andrew.cooper3@citrix.com>,
        "Bae, Chang Seok" <chang.seok.bae@intel.com>
References: <BYAPR11MB325685AB8E3DFD245846F854A9939@BYAPR11MB3256.namprd11.prod.outlook.com>
 <878rxn6h6t.ffs@tglx> <16BF8BE6-B7B1-4F3E-B972-9D82CD2F23C8@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <16BF8BE6-B7B1-4F3E-B972-9D82CD2F23C8@intel.com>
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On 11/17/21 05:52, Nakajima, Jun wrote:
> If a (creative) guest wants to set XFD[AMX] = 1 for fun while keeping
> AMX state alive without saving the AXM state, it may lose the state
> after VM exit/entry.

I think this should not happen, unless you also document that other 
random events (hypothetically, it could be some other core using AMX?) 
can cause the loss of XTILEDATA if XFD[AMX]=1.  Virtualization should 
not be special, I'd prefer that the guest has the same behavior as bare 
metal in this respect.

Paolo