linux-kernel - Re: [PATCH 3/3] KVM: Move coalesced MMIO initialization (back) into kvm_create

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Message-ID: <YvvcHitVaf2EDAj0@google.com>
Date:   Tue, 16 Aug 2022 18:04:14 +0000
From:   Oliver Upton <oliver.upton@...ux.dev>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+744e173caec2e1627ee0@...kaller.appspotmail.com,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH 3/3] KVM: Move coalesced MMIO initialization (back) into
 kvm_create_vm()

On Tue, Aug 16, 2022 at 05:39:37AM +0000, Sean Christopherson wrote:
> Invoke kvm_coalesced_mmio_init() from kvm_create_vm() now that allocating
> and initializing coalesced MMIO objects is separate from registering any
> associated devices.  Moving coalesced MMIO cleans up the last oddity
> where KVM does VM creation/initialization after kvm_create_vm(), and more
> importantly after kvm_arch_post_init_vm() is called and the VM is added
> to the global vm_list, i.e. after the VM is fully created as far as KVM
> is concerned.
> 
> Originally, kvm_coalesced_mmio_init() was called by kvm_create_vm(), but
> the original implementation was completely devoid of error handling.
> Commit 6ce5a090a9a0 ("KVM: coalesced_mmio: fix kvm_coalesced_mmio_init()'s
> error handling" fixed the various bugs, and in doing so rightly moved the
> call to after kvm_create_vm() because kvm_coalesced_mmio_init() also
> registered the coalesced MMIO device.  Commit 2b3c246a682c ("KVM: Make
> coalesced mmio use a device per zone") cleaned up that mess by having
> each zone register a separate device, i.e. moved device registration to
> its logical home in kvm_vm_ioctl_register_coalesced_mmio().  As a result,
> kvm_coalesced_mmio_init() is now a "pure" initialization helper and can
> be safely called from kvm_create_vm().
> 
> Opportunstically drop the #ifdef, KVM provides stubs for
> kvm_coalesced_mmio_{init,free}() when CONFIG_KVM_MMIO=n (arm).
							   ^^^
We have CONFIG_KVM_MMIO=y on arm64. Is it actually s390?

--
Thanks,
Oliver