linux-kernel - Re: [PATCH RESEND v2 03/17] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP

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Message-ID: <851bd9ed-3ff3-6aef-725c-b586d819211c@redhat.com>
Date:   Mon, 23 Dec 2019 18:59:01 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Christophe de Dinechin <dinechin@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH RESEND v2 03/17] KVM: X86: Don't track dirty for
 KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]

On 23/12/19 18:27, Peter Xu wrote:
> Yes.  Though it is a bit tricky in that then we'll also need to make
> sure to take slots_lock or srcu to protect that hva (say, we must drop
> that hva reference before we release the locks, otherwise the hva
> could gone under us, iiuc).

Yes, kvm->slots_lock is taken by x86_set_memory_region.  We need to move
that to the callers, of which several are already taking the lock (all
except vmx_set_tss_addr and kvm_arch_destroy_vm).

Paolo

> So if we want to do that we'd better
> comment on that hva value very explicitly, just in case some future
> callers of __x86_set_memory_region could cache it somewhere.