linux-kernel - Re: [RFC KVM 02/27] KVM: x86: Introduce address_space

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Date:   Mon, 13 May 2019 17:55:44 +0200
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        kvm list <kvm@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        jan.setjeeilers@...cle.com, Liran Alon <liran.alon@...cle.com>,
        Jonathan Adams <jwadams@...gle.com>
Subject: Re: [RFC KVM 02/27] KVM: x86: Introduce address_space_isolation
 module parameter



On 5/13/19 5:46 PM, Andy Lutomirski wrote:
> On Mon, May 13, 2019 at 7:39 AM Alexandre Chartre
> <alexandre.chartre@...cle.com> wrote:
>>
>> From: Liran Alon <liran.alon@...cle.com>
>>
>> Add the address_space_isolation parameter to the kvm module.
>>
>> When set to true, KVM #VMExit handlers run in isolated address space
>> which maps only KVM required code and per-VM information instead of
>> entire kernel address space.
> 
> Does the *entry* also get isolated?  If not, it seems less useful for
> side-channel mitigation.
> 

Yes, context is switched before VM entry. We switch back to kernel address
space if VM-exit handler needs it or when exiting the KVM_RUN ioctl.

alex.