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

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Date:   Tue, 16 Aug 2022 05:39:37 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+744e173caec2e1627ee0@...kaller.appspotmail.com,
        Oliver Upton <oliver.upton@...ux.dev>,
        Sean Christopherson <seanjc@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: [PATCH 3/3] KVM: Move coalesced MMIO initialization (back) into kvm_create_vm()

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).

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/kvm_main.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 15e304e059d4..44b92d773156 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1214,6 +1214,10 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 	if (r)
 		goto out_err_no_mmu_notifier;

+	r = kvm_coalesced_mmio_init(kvm);
+	if (r < 0)
+		goto out_no_coalesced_mmio;
+
 	r = kvm_create_vm_debugfs(kvm, fdname);
 	if (r)
 		goto out_err_no_debugfs;
@@ -1234,6 +1238,8 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 out_err:
 	kvm_destroy_vm_debugfs(kvm);
 out_err_no_debugfs:
+	kvm_coalesced_mmio_free(kvm);
+out_no_coalesced_mmio:
 #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
 	if (kvm->mmu_notifier.ops)
 		mmu_notifier_unregister(&kvm->mmu_notifier, current->mm);
@@ -4907,11 +4913,6 @@ static int kvm_dev_ioctl_create_vm(unsigned long type)
 		goto put_fd;
 	}

-#ifdef CONFIG_KVM_MMIO
-	r = kvm_coalesced_mmio_init(kvm);
-	if (r < 0)
-		goto put_kvm;
-#endif
 	file = anon_inode_getfile("kvm-vm", &kvm_vm_fops, kvm, O_RDWR);
 	if (IS_ERR(file)) {
 		r = PTR_ERR(file);
-- 
2.37.1.595.g718a3a8f04-goog