Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
Message-ID: <d513db49-bb94-becf-be7e-f26dceb3e1bf@redhat.com>
Date:   Tue, 14 Dec 2021 11:16:12 +0100
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Subject: Re: [PATCH 09/19] kvm: x86: Prepare reallocation check
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To:     "Tian, Kevin" <kevin.tian@intel.com>,
        "Zhong, Yang" <yang.zhong@intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>
Cc:     "Christopherson,, Sean" <seanjc@google.com>,
        "Nakajima, Jun" <jun.nakajima@intel.com>,
        "jing2.liu@linux.intel.com" <jing2.liu@linux.intel.com>,
        "Liu, Jing2" <jing2.liu@intel.com>
References: <20211208000359.2853257-1-yang.zhong@intel.com>
 <20211208000359.2853257-10-yang.zhong@intel.com>
 <fc113a81-b5b8-aaae-5799-c6d49b77b2b4@redhat.com>
 <BN9PR11MB5276416CED5892C20F56EB888C759@BN9PR11MB5276.namprd11.prod.outlook.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <BN9PR11MB5276416CED5892C20F56EB888C759@BN9PR11MB5276.namprd11.prod.outlook.com>
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On 12/14/21 08:06, Tian, Kevin wrote:
>> - if (dynamic_enabled & ~guest_fpu->user_perm) != 0, then this is a
>> userspace error and you can #GP the guest without any issue.  Userspace
>> is buggy
>
> Is it a general guideline that an error caused by emulation itself (e.g.
> due to no memory) can be reflected into the guest as #GP, even
> when from guest p.o.v there is nothing wrong with its setting?

No memory is a tricky one, if possible it should propagate -ENOMEM up to 
KVM_RUN or KVM_SET_MSR.  But it's basically an impossible case anyway, 
because even with 8K TILEDATA we're within the limit of 
PAGE_ALLOC_COSTLY_ORDER.

So, since it's not easy to do it right now, we can look at it later.

Paolo