linux-kernel - Re: [PATCH 09/19] kvm: x86: Prepare reallocation check

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Date:   Tue, 14 Dec 2021 11:16:12 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Zhong, Yang" <yang.zhong@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Cc:     "Christopherson,, Sean" <seanjc@...gle.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        "jing2.liu@...ux.intel.com" <jing2.liu@...ux.intel.com>,
        "Liu, Jing2" <jing2.liu@...el.com>
Subject: Re: [PATCH 09/19] kvm: x86: Prepare reallocation check

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