linux-kernel - Re: [PATCH 4/6] KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET

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Date:   Thu, 1 Apr 2021 19:33:12 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 4/6] KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET_SREGS2

On 01/04/21 19:10, Maxim Levitsky wrote:
> I haven't yet studied in depth the locking that is used in the kvm,
> so I put this to be on the safe side.
> 
> I looked at it a bit and it looks like the pdptr reading code takes
> this lock because it accesses the memslots, which is not done here,
> and therefore the lock is indeed not needed here.
> 
> I need to study in depth how locking is done in kvm to be 100% sure
> about this.

Yes, SRCU protects reading the memslots (and therefore accessing guest 
memory).

>> 195, not 196.
> 
> I am also planning to add KVM_CAP_SET_GUEST_DEBUG2 for which I
> used 195.

Sounds good then.

Paolo