[v1] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

[PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

Posted by Pierre Morel 3 years, 7 months ago

We have a cross dependency between KVM and VFIO.
To be able to keep both subsystem modular we add a registering
hook inside the S390 core code.

This fixes a build problem when VFIO is built-in and KVM is built
as a module or excluded.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
Cc: <stable@vger.kernel.org>
---
 arch/s390/include/asm/kvm_host.h | 17 ++++++-----------
 arch/s390/kvm/pci.c              | 10 ++++++----
 arch/s390/pci/Makefile           |  2 ++
 arch/s390/pci/pci_kvm_hook.c     | 11 +++++++++++
 drivers/vfio/pci/vfio_pci_zdev.c |  8 ++++++--
 5 files changed, 31 insertions(+), 17 deletions(-)
 create mode 100644 arch/s390/pci/pci_kvm_hook.c

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index f39092e0ceaa..8312ed9d1937 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -1038,16 +1038,11 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
 #define __KVM_HAVE_ARCH_VM_FREE
 void kvm_arch_free_vm(struct kvm *kvm);
 
-#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
-int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
-void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
-#else
-static inline int kvm_s390_pci_register_kvm(struct zpci_dev *dev,
-					    struct kvm *kvm)
-{
-	return -EPERM;
-}
-static inline void kvm_s390_pci_unregister_kvm(struct zpci_dev *dev) {}
-#endif
+struct kvm_register_hook {
+	int (*kvm_register)(void *opaque, struct kvm *kvm);
+	void (*kvm_unregister)(void *opaque);
+};
+
+extern struct kvm_register_hook kvm_pci_hook;
 
 #endif
diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
index 4946fb7757d6..e173fce64c4f 100644
--- a/arch/s390/kvm/pci.c
+++ b/arch/s390/kvm/pci.c
@@ -431,8 +431,9 @@ static void kvm_s390_pci_dev_release(struct zpci_dev *zdev)
  * available, enable them and let userspace indicate whether or not they will
  * be used (specify SHM bit to disable).
  */
-int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
+static int kvm_s390_pci_register_kvm(void *opaque, struct kvm *kvm)
 {
+	struct zpci_dev *zdev = opaque;
 	int rc;
 
 	if (!zdev)
@@ -510,10 +511,10 @@ int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
 	kvm_put_kvm(kvm);
 	return rc;
 }
-EXPORT_SYMBOL_GPL(kvm_s390_pci_register_kvm);
 
-void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
+static void kvm_s390_pci_unregister_kvm(void *opaque)
 {
+	struct zpci_dev *zdev = opaque;
 	struct kvm *kvm;
 
 	if (!zdev)
@@ -566,7 +567,6 @@ void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
 
 	kvm_put_kvm(kvm);
 }
-EXPORT_SYMBOL_GPL(kvm_s390_pci_unregister_kvm);
 
 void kvm_s390_pci_init_list(struct kvm *kvm)
 {
@@ -678,6 +678,8 @@ int kvm_s390_pci_init(void)
 
 	spin_lock_init(&aift->gait_lock);
 	mutex_init(&aift->aift_lock);
+	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
+	kvm_pci_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
 
 	return 0;
 }
diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
index bf557a1b789c..c02dbfb415d9 100644
--- a/arch/s390/pci/Makefile
+++ b/arch/s390/pci/Makefile
@@ -7,3 +7,5 @@ obj-$(CONFIG_PCI)	+= pci.o pci_irq.o pci_dma.o pci_clp.o pci_sysfs.o \
 			   pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
 			   pci_bus.o
 obj-$(CONFIG_PCI_IOV)	+= pci_iov.o
+
+obj-y += pci_kvm_hook.o
diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
new file mode 100644
index 000000000000..9d8799b72dbf
--- /dev/null
+++ b/arch/s390/pci/pci_kvm_hook.c
@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * VFIO ZPCI devices support
+ *
+ * Copyright (C) IBM Corp. 2022.  All rights reserved.
+ *	Author(s): Pierre Morel <pmorel@linux.ibm.com>
+ */
+#include <linux/kvm_host.h>
+
+struct kvm_register_hook kvm_pci_hook;
+EXPORT_SYMBOL_GPL(kvm_pci_hook);
diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
index e163aa9f6144..3b7a707e2fe5 100644
--- a/drivers/vfio/pci/vfio_pci_zdev.c
+++ b/drivers/vfio/pci/vfio_pci_zdev.c
@@ -151,7 +151,10 @@ int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
 	if (!vdev->vdev.kvm)
 		return 0;
 
-	return kvm_s390_pci_register_kvm(zdev, vdev->vdev.kvm);
+	if (kvm_pci_hook.kvm_register)
+		return kvm_pci_hook.kvm_register(zdev, vdev->vdev.kvm);
+
+	return -ENOENT;
 }
 
 void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
@@ -161,5 +164,6 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
 	if (!zdev || !vdev->vdev.kvm)
 		return;
 
-	kvm_s390_pci_unregister_kvm(zdev);
+	if (kvm_pci_hook.kvm_unregister)
+		return kvm_pci_hook.kvm_unregister(zdev);
 }
-- 
2.31.1

Re: [PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

Posted by Matthew Rosato 3 years, 7 months ago

On 8/18/22 6:23 AM, Pierre Morel wrote:
> We have a cross dependency between KVM and VFIO.

maybe add something like 'when using s390 vfio_pci_zdev extensions for PCI passthrough'

> To be able to keep both subsystem modular we add a registering
> hook inside the S390 core code.
> 
> This fixes a build problem when VFIO is built-in and KVM is built
> as a module or excluded.

s/or excluded//

There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.

> 
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
> Cc: <stable@vger.kernel.org>
> ---
>  arch/s390/include/asm/kvm_host.h | 17 ++++++-----------
>  arch/s390/kvm/pci.c              | 10 ++++++----
>  arch/s390/pci/Makefile           |  2 ++
>  arch/s390/pci/pci_kvm_hook.c     | 11 +++++++++++
>  drivers/vfio/pci/vfio_pci_zdev.c |  8 ++++++--
>  5 files changed, 31 insertions(+), 17 deletions(-)
>  create mode 100644 arch/s390/pci/pci_kvm_hook.c
> 
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index f39092e0ceaa..8312ed9d1937 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -1038,16 +1038,11 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
>  #define __KVM_HAVE_ARCH_VM_FREE
>  void kvm_arch_free_vm(struct kvm *kvm);
>  
> -#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
> -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
> -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
> -#else
> -static inline int kvm_s390_pci_register_kvm(struct zpci_dev *dev,
> -					    struct kvm *kvm)
> -{
> -	return -EPERM;
> -}
> -static inline void kvm_s390_pci_unregister_kvm(struct zpci_dev *dev) {}
> -#endif
> +struct kvm_register_hook {

Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.

> +	int (*kvm_register)(void *opaque, struct kvm *kvm);
> +	void (*kvm_unregister)(void *opaque);
> +};
> +
> +extern struct kvm_register_hook kvm_pci_hook;

Nit: kvm_zpci_hook ?

>  
>  #endif
> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
> index 4946fb7757d6..e173fce64c4f 100644
> --- a/arch/s390/kvm/pci.c
> +++ b/arch/s390/kvm/pci.c
> @@ -431,8 +431,9 @@ static void kvm_s390_pci_dev_release(struct zpci_dev *zdev)
>   * available, enable them and let userspace indicate whether or not they will
>   * be used (specify SHM bit to disable).
>   */
> -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
> +static int kvm_s390_pci_register_kvm(void *opaque, struct kvm *kvm)
>  {
> +	struct zpci_dev *zdev = opaque;
>  	int rc;
>  
>  	if (!zdev)
> @@ -510,10 +511,10 @@ int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
>  	kvm_put_kvm(kvm);
>  	return rc;
>  }
> -EXPORT_SYMBOL_GPL(kvm_s390_pci_register_kvm);
>  
> -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
> +static void kvm_s390_pci_unregister_kvm(void *opaque)
>  {
> +	struct zpci_dev *zdev = opaque;
>  	struct kvm *kvm;
>  
>  	if (!zdev)
> @@ -566,7 +567,6 @@ void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
>  
>  	kvm_put_kvm(kvm);
>  }
> -EXPORT_SYMBOL_GPL(kvm_s390_pci_unregister_kvm);
>  
>  void kvm_s390_pci_init_list(struct kvm *kvm)
>  {
> @@ -678,6 +678,8 @@ int kvm_s390_pci_init(void)
>  
>  	spin_lock_init(&aift->gait_lock);
>  	mutex_init(&aift->aift_lock);
> +	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
> +	kvm_pci_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
>  
>  	return 0;
>  }
> diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
> index bf557a1b789c..c02dbfb415d9 100644
> --- a/arch/s390/pci/Makefile
> +++ b/arch/s390/pci/Makefile
> @@ -7,3 +7,5 @@ obj-$(CONFIG_PCI)	+= pci.o pci_irq.o pci_dma.o pci_clp.o pci_sysfs.o \
>  			   pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
>  			   pci_bus.o
>  obj-$(CONFIG_PCI_IOV)	+= pci_iov.o
> +
> +obj-y += pci_kvm_hook.o

I guess it doesn't harm anything to add this unconditionally, but I think it would also be OK to just include this in the CONFIG_PCI list - vfio_pci_zdev and arch/s390/kvm/pci all rely on CONFIG_PCI via CONFIG_VFIO_PCI_ZDEV_KVM which implies PCI via VFIO_PCI.

> diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
> new file mode 100644
> index 000000000000..9d8799b72dbf
> --- /dev/null
> +++ b/arch/s390/pci/pci_kvm_hook.c
> @@ -0,0 +1,11 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * VFIO ZPCI devices support
> + *
> + * Copyright (C) IBM Corp. 2022.  All rights reserved.
> + *	Author(s): Pierre Morel <pmorel@linux.ibm.com>
> + */
> +#include <linux/kvm_host.h>
> +
> +struct kvm_register_hook kvm_pci_hook;
> +EXPORT_SYMBOL_GPL(kvm_pci_hook);

Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?

I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.

> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
> index e163aa9f6144..3b7a707e2fe5 100644
> --- a/drivers/vfio/pci/vfio_pci_zdev.c
> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
> @@ -151,7 +151,10 @@ int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
>  	if (!vdev->vdev.kvm)
>  		return 0;
>  
> -	return kvm_s390_pci_register_kvm(zdev, vdev->vdev.kvm);
> +	if (kvm_pci_hook.kvm_register)
> +		return kvm_pci_hook.kvm_register(zdev, vdev->vdev.kvm);
> +
> +	return -ENOENT;
>  }
>  
>  void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
> @@ -161,5 +164,6 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>  	if (!zdev || !vdev->vdev.kvm)
>  		return;
>  
> -	kvm_s390_pci_unregister_kvm(zdev);
> +	if (kvm_pci_hook.kvm_unregister)
> +		return kvm_pci_hook.kvm_unregister(zdev);

No need for the return here, this is a void function calling a void function.


Overall, this looks good to me and survives a series of compile and device passthrough tests on my end, just a matter of a few of these minor comments above.  Thanks for tackling this Pierre!

Re: [PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

Posted by Niklas Schnelle 3 years, 7 months ago

On Thu, 2022-08-18 at 09:33 -0400, Matthew Rosato wrote:
> On 8/18/22 6:23 AM, Pierre Morel wrote:
> > We have a cross dependency between KVM and VFIO.
> 
> maybe add something like 'when using s390 vfio_pci_zdev extensions for PCI passthrough'
> 
> > To be able to keep both subsystem modular we add a registering
> > hook inside the S390 core code.
> > 
> > This fixes a build problem when VFIO is built-in and KVM is built
> > as a module or excluded.
> 
> s/or excluded//
> 
> There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.
> 
> > Reported-by: Randy Dunlap <rdunlap@infradead.org>
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> > Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
> > Cc: <stable@vger.kernel.org>
> > ---
> >  arch/s390/include/asm/kvm_host.h | 17 ++++++-----------
> >  arch/s390/kvm/pci.c              | 10 ++++++----
> >  arch/s390/pci/Makefile           |  2 ++
> >  arch/s390/pci/pci_kvm_hook.c     | 11 +++++++++++
> >  drivers/vfio/pci/vfio_pci_zdev.c |  8 ++++++--
> >  5 files changed, 31 insertions(+), 17 deletions(-)
> >  create mode 100644 arch/s390/pci/pci_kvm_hook.c
> > 
> > diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> > index f39092e0ceaa..8312ed9d1937 100644
> > --- a/arch/s390/include/asm/kvm_host.h
> > +++ b/arch/s390/include/asm/kvm_host.h

I added Janosch as second S390 KVM maintainer in case he wants to chime
in.

> > @@ -1038,16 +1038,11 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
> >  #define __KVM_HAVE_ARCH_VM_FREE
> >  void kvm_arch_free_vm(struct kvm *kvm);
> >  
> > -#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
> > -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
> > -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
> > -#else
> > -static inline int kvm_s390_pci_register_kvm(struct zpci_dev *dev,
> > -					    struct kvm *kvm)
> > -{
> > -	return -EPERM;
> > -}
> > -static inline void kvm_s390_pci_unregister_kvm(struct zpci_dev *dev) {}
> > -#endif
> > +struct kvm_register_hook {
> 
> Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.

Hmm, I guess one could re-use the same struct for another such KVM
dependency but I lean towards the same thinking as Matt, for now this
is for zpci so stay specific we can always generalize later.

Nit: For me hook and register together sound a bit redudant, maybe
"zpci_kvm_register"? Also question for Matt as a native speaker, should
it rather be "registration" when used as a noun here?


> 
> > +	int (*kvm_register)(void *opaque, struct kvm *kvm);
> > +	void (*kvm_unregister)(void *opaque);

I do wonder if this needs to be opague "struct zpci_dev" should be
defined even if CONFIG_PCI is unset.


> > +};
> > +
> > +extern struct kvm_register_hook kvm_pci_hook;
> 
> Nit: kvm_zpci_hook ?

Analogous to zpci_kvm_regist(er|ration) I would call the variable
simply zpci_kvm i.e. the type is a registration and the variable is the
instance of it that links zpci and kvm.

> 
> >  
> >  #endif
> > diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
> > index 4946fb7757d6..e173fce64c4f 100644
> > --- a/arch/s390/kvm/pci.c
> > +++ b/arch/s390/kvm/pci.c
> > @@ -431,8 +431,9 @@ static void kvm_s390_pci_dev_release(struct zpci_dev *zdev)
> >   * available, enable them and let userspace indicate whether or not they will
> >   * be used (specify SHM bit to disable).
> >   */
> > -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
> > +static int kvm_s390_pci_register_kvm(void *opaque, struct kvm *kvm)
> >  {
> > +	struct zpci_dev *zdev = opaque;
> >  	int rc;
> >  
> >  	if (!zdev)
> > @@ -510,10 +511,10 @@ int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
> >  	kvm_put_kvm(kvm);
> >  	return rc;
> >  }
> > -EXPORT_SYMBOL_GPL(kvm_s390_pci_register_kvm);
> >  
> > -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
> > +static void kvm_s390_pci_unregister_kvm(void *opaque)
> >  {
> > +	struct zpci_dev *zdev = opaque;
> >  	struct kvm *kvm;
> >  
> >  	if (!zdev)
> > @@ -566,7 +567,6 @@ void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
> >  
> >  	kvm_put_kvm(kvm);
> >  }
> > -EXPORT_SYMBOL_GPL(kvm_s390_pci_unregister_kvm);
> >  
> >  void kvm_s390_pci_init_list(struct kvm *kvm)
> >  {
> > @@ -678,6 +678,8 @@ int kvm_s390_pci_init(void)
> >  
> >  	spin_lock_init(&aift->gait_lock);
> >  	mutex_init(&aift->aift_lock);
> > +	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
> > +	kvm_pci_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
> >  
> >  	return 0;
> >  }
> > diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
> > index bf557a1b789c..c02dbfb415d9 100644
> > --- a/arch/s390/pci/Makefile
> > +++ b/arch/s390/pci/Makefile
> > @@ -7,3 +7,5 @@ obj-$(CONFIG_PCI)	+= pci.o pci_irq.o pci_dma.o pci_clp.o pci_sysfs.o \
> >  			   pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
> >  			   pci_bus.o
> >  obj-$(CONFIG_PCI_IOV)	+= pci_iov.o
> > +
> > +obj-y += pci_kvm_hook.o
> 
> I guess it doesn't harm anything to add this unconditionally, but I think it would also be OK to just include this in the CONFIG_PCI list - vfio_pci_zdev and arch/s390/kvm/pci all rely on CONFIG_PCI via CONFIG_VFIO_PCI_ZDEV_KVM which implies PCI via VFIO_PCI.
> 
> > diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
> > new file mode 100644
> > index 000000000000..9d8799b72dbf
> > --- /dev/null
> > +++ b/arch/s390/pci/pci_kvm_hook.c
> > @@ -0,0 +1,11 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * VFIO ZPCI devices support
> > + *
> > + * Copyright (C) IBM Corp. 2022.  All rights reserved.
> > + *	Author(s): Pierre Morel <pmorel@linux.ibm.com>
> > + */
> > +#include <linux/kvm_host.h>
> > +
> > +struct kvm_register_hook kvm_pci_hook;
> > +EXPORT_SYMBOL_GPL(kvm_pci_hook);
> 
> Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?
> 
> I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.

I'm fine with a separate file, pci.c is long enough as it is. I also
don't have a problem with having it maintained as part of S390 PCI but
logically I think it does fall more under arch/kvm/pci* so one could
argue it should be added in the MAINTAINERS file in that section.
If you change the struct name as I proposed above I would probably go
with "pci_kvm_register.c"

> 
> > diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
> > index e163aa9f6144..3b7a707e2fe5 100644
> > --- a/drivers/vfio/pci/vfio_pci_zdev.c
> > +++ b/drivers/vfio/pci/vfio_pci_zdev.c
> > @@ -151,7 +151,10 @@ int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
> >  	if (!vdev->vdev.kvm)
> >  		return 0;
> >  
> > -	return kvm_s390_pci_register_kvm(zdev, vdev->vdev.kvm);
> > +	if (kvm_pci_hook.kvm_register)
> > +		return kvm_pci_hook.kvm_register(zdev, vdev->vdev.kvm);
> > +
> > +	return -ENOENT;
> >  }
> >  
> >  void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
> > @@ -161,5 +164,6 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
> >  	if (!zdev || !vdev->vdev.kvm)
> >  		return;
> >  
> > -	kvm_s390_pci_unregister_kvm(zdev);
> > +	if (kvm_pci_hook.kvm_unregister)
> > +		return kvm_pci_hook.kvm_unregister(zdev);
> 
> No need for the return here, this is a void function calling a void function.
> 
> 
> Overall, this looks good to me and survives a series of compile and device passthrough tests on my end, just a matter of a few of these minor comments above.  Thanks for tackling this Pierre!

Yes I agree, overall this looks good to me though I'm admittedly not
very knowledgable about how to best handle module dependencies like
this. It does look cleaner than  the symbol_get() alternative we
discussed.

Re: [PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

Posted by Matthew Rosato 3 years, 7 months ago

On 8/18/22 10:20 AM, Niklas Schnelle wrote:
> On Thu, 2022-08-18 at 09:33 -0400, Matthew Rosato wrote:
>> On 8/18/22 6:23 AM, Pierre Morel wrote:
>>> We have a cross dependency between KVM and VFIO.
>>
>> maybe add something like 'when using s390 vfio_pci_zdev extensions for PCI passthrough'
>>
>>> To be able to keep both subsystem modular we add a registering
>>> hook inside the S390 core code.
>>>
>>> This fixes a build problem when VFIO is built-in and KVM is built
>>> as a module or excluded.
>>
>> s/or excluded//
>>
>> There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.
>>
>>> Reported-by: Randy Dunlap <rdunlap@infradead.org>
>>> Reported-by: kernel test robot <lkp@intel.com>
>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>> Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
>>> Cc: <stable@vger.kernel.org>
>>> ---
>>>  arch/s390/include/asm/kvm_host.h | 17 ++++++-----------
>>>  arch/s390/kvm/pci.c              | 10 ++++++----
>>>  arch/s390/pci/Makefile           |  2 ++
>>>  arch/s390/pci/pci_kvm_hook.c     | 11 +++++++++++
>>>  drivers/vfio/pci/vfio_pci_zdev.c |  8 ++++++--
>>>  5 files changed, 31 insertions(+), 17 deletions(-)
>>>  create mode 100644 arch/s390/pci/pci_kvm_hook.c
>>>
>>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>>> index f39092e0ceaa..8312ed9d1937 100644
>>> --- a/arch/s390/include/asm/kvm_host.h
>>> +++ b/arch/s390/include/asm/kvm_host.h
> 
> I added Janosch as second S390 KVM maintainer in case he wants to chime
> in.
> 
>>> @@ -1038,16 +1038,11 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
>>>  #define __KVM_HAVE_ARCH_VM_FREE
>>>  void kvm_arch_free_vm(struct kvm *kvm);
>>>  
>>> -#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
>>> -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
>>> -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
>>> -#else
>>> -static inline int kvm_s390_pci_register_kvm(struct zpci_dev *dev,
>>> -					    struct kvm *kvm)
>>> -{
>>> -	return -EPERM;
>>> -}
>>> -static inline void kvm_s390_pci_unregister_kvm(struct zpci_dev *dev) {}
>>> -#endif
>>> +struct kvm_register_hook {
>>
>> Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.
> 
> Hmm, I guess one could re-use the same struct for another such KVM
> dependency but I lean towards the same thinking as Matt, for now this
> is for zpci so stay specific we can always generalize later.

Yes, let's keep this zpci-specific. 

> 
> Nit: For me hook and register together sound a bit redudant, maybe
> "zpci_kvm_register"? Also question for Matt as a native speaker, should
> it rather be "registration" when used as a noun here?
> 

Maybe just drop the 'register'.  If there is a need for a 3rd function later, for example, it might not be related to registration.

e.g. struct kvm_zpci_hook {
   ...
};

extern struct kvm_zpci_hook zpci_kvm;

> 
>>
>>> +	int (*kvm_register)(void *opaque, struct kvm *kvm);
>>> +	void (*kvm_unregister)(void *opaque);
> 
> I do wonder if this needs to be opague "struct zpci_dev" should be
> defined even if CONFIG_PCI is unset.
> 
> 
>>> +};
>>> +
>>> +extern struct kvm_register_hook kvm_pci_hook;
>>
>> Nit: kvm_zpci_hook ?
> 
> Analogous to zpci_kvm_regist(er|ration) I would call the variable
> simply zpci_kvm i.e. the type is a registration and the variable is the
> instance of it that links zpci and kvm.
> 

Yeah, see above.

>>
>>>  
>>>  #endif
>>> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
>>> index 4946fb7757d6..e173fce64c4f 100644
>>> --- a/arch/s390/kvm/pci.c
>>> +++ b/arch/s390/kvm/pci.c
>>> @@ -431,8 +431,9 @@ static void kvm_s390_pci_dev_release(struct zpci_dev *zdev)
>>>   * available, enable them and let userspace indicate whether or not they will
>>>   * be used (specify SHM bit to disable).
>>>   */
>>> -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
>>> +static int kvm_s390_pci_register_kvm(void *opaque, struct kvm *kvm)
>>>  {
>>> +	struct zpci_dev *zdev = opaque;
>>>  	int rc;
>>>  
>>>  	if (!zdev)
>>> @@ -510,10 +511,10 @@ int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
>>>  	kvm_put_kvm(kvm);
>>>  	return rc;
>>>  }
>>> -EXPORT_SYMBOL_GPL(kvm_s390_pci_register_kvm);
>>>  
>>> -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
>>> +static void kvm_s390_pci_unregister_kvm(void *opaque)
>>>  {
>>> +	struct zpci_dev *zdev = opaque;
>>>  	struct kvm *kvm;
>>>  
>>>  	if (!zdev)
>>> @@ -566,7 +567,6 @@ void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
>>>  
>>>  	kvm_put_kvm(kvm);
>>>  }
>>> -EXPORT_SYMBOL_GPL(kvm_s390_pci_unregister_kvm);
>>>  
>>>  void kvm_s390_pci_init_list(struct kvm *kvm)
>>>  {
>>> @@ -678,6 +678,8 @@ int kvm_s390_pci_init(void)
>>>  
>>>  	spin_lock_init(&aift->gait_lock);
>>>  	mutex_init(&aift->aift_lock);
>>> +	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
>>> +	kvm_pci_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
>>>  
>>>  	return 0;
>>>  }
>>> diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
>>> index bf557a1b789c..c02dbfb415d9 100644
>>> --- a/arch/s390/pci/Makefile
>>> +++ b/arch/s390/pci/Makefile
>>> @@ -7,3 +7,5 @@ obj-$(CONFIG_PCI)	+= pci.o pci_irq.o pci_dma.o pci_clp.o pci_sysfs.o \
>>>  			   pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
>>>  			   pci_bus.o
>>>  obj-$(CONFIG_PCI_IOV)	+= pci_iov.o
>>> +
>>> +obj-y += pci_kvm_hook.o
>>
>> I guess it doesn't harm anything to add this unconditionally, but I think it would also be OK to just include this in the CONFIG_PCI list - vfio_pci_zdev and arch/s390/kvm/pci all rely on CONFIG_PCI via CONFIG_VFIO_PCI_ZDEV_KVM which implies PCI via VFIO_PCI.
>>
>>> diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
>>> new file mode 100644
>>> index 000000000000..9d8799b72dbf
>>> --- /dev/null
>>> +++ b/arch/s390/pci/pci_kvm_hook.c
>>> @@ -0,0 +1,11 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +/*
>>> + * VFIO ZPCI devices support
>>> + *
>>> + * Copyright (C) IBM Corp. 2022.  All rights reserved.
>>> + *	Author(s): Pierre Morel <pmorel@linux.ibm.com>
>>> + */
>>> +#include <linux/kvm_host.h>
>>> +
>>> +struct kvm_register_hook kvm_pci_hook;
>>> +EXPORT_SYMBOL_GPL(kvm_pci_hook);
>>
>> Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?
>>
>> I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.
> 
> I'm fine with a separate file, pci.c is long enough as it is. I also
> don't have a problem with having it maintained as part of S390 PCI but
> logically I think it does fall more under arch/kvm/pci* so one could
> argue it should be added in the MAINTAINERS file in that section.
> If you change the struct name as I proposed above I would probably go
> with "pci_kvm_register.c"

OK, no problem with me for a separate file then, or maintaining said file.  But I guess not pci_kvm_register.c per my comments above

> 
>>
>>> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
>>> index e163aa9f6144..3b7a707e2fe5 100644
>>> --- a/drivers/vfio/pci/vfio_pci_zdev.c
>>> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
>>> @@ -151,7 +151,10 @@ int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
>>>  	if (!vdev->vdev.kvm)
>>>  		return 0;
>>>  
>>> -	return kvm_s390_pci_register_kvm(zdev, vdev->vdev.kvm);
>>> +	if (kvm_pci_hook.kvm_register)
>>> +		return kvm_pci_hook.kvm_register(zdev, vdev->vdev.kvm);
>>> +
>>> +	return -ENOENT;
>>>  }
>>>  
>>>  void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>>> @@ -161,5 +164,6 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>>>  	if (!zdev || !vdev->vdev.kvm)
>>>  		return;
>>>  
>>> -	kvm_s390_pci_unregister_kvm(zdev);
>>> +	if (kvm_pci_hook.kvm_unregister)
>>> +		return kvm_pci_hook.kvm_unregister(zdev);
>>
>> No need for the return here, this is a void function calling a void function.
>>
>>
>> Overall, this looks good to me and survives a series of compile and device passthrough tests on my end, just a matter of a few of these minor comments above.  Thanks for tackling this Pierre!
> 
> Yes I agree, overall this looks good to me though I'm admittedly not
> very knowledgable about how to best handle module dependencies like
> this. It does look cleaner than  the symbol_get() alternative we
> discussed. 
> 
>

Re: [PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

Posted by Niklas Schnelle 3 years, 7 months ago

On Thu, 2022-08-18 at 11:13 -0400, Matthew Rosato wrote:
> On 8/18/22 10:20 AM, Niklas Schnelle wrote:
> > On Thu, 2022-08-18 at 09:33 -0400, Matthew Rosato wrote:
> > > On 8/18/22 6:23 AM, Pierre Morel wrote:
> > > > We have a cross dependency between KVM and VFIO.
> > > 
> > > maybe add something like 'when using s390 vfio_pci_zdev extensions for PCI passthrough'
> > > 
> > > > To be able to keep both subsystem modular we add a registering
> > > > hook inside the S390 core code.
> > > > 
> > > > This fixes a build problem when VFIO is built-in and KVM is built
> > > > as a module or excluded.
> > > 
> > > s/or excluded//
> > > 
> > > There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.
> > > 
> > > > Reported-by: Randy Dunlap <rdunlap@infradead.org>
> > > > Reported-by: kernel test robot <lkp@intel.com>
> > > > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> > > > Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
> > > > Cc: <stable@vger.kernel.org>
> > > > ---
> > > >  arch/s390/include/asm/kvm_host.h | 17 ++++++-----------
> > > >  arch/s390/kvm/pci.c              | 10 ++++++----
> > > >  arch/s390/pci/Makefile           |  2 ++
> > > >  arch/s390/pci/pci_kvm_hook.c     | 11 +++++++++++
> > > >  drivers/vfio/pci/vfio_pci_zdev.c |  8 ++++++--
> > > >  5 files changed, 31 insertions(+), 17 deletions(-)
> > > >  create mode 100644 arch/s390/pci/pci_kvm_hook.c
> > > > 
> > > > diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> > > > index f39092e0ceaa..8312ed9d1937 100644
> > > > --- a/arch/s390/include/asm/kvm_host.h
> > > > +++ b/arch/s390/include/asm/kvm_host.h
> > 
> > I added Janosch as second S390 KVM maintainer in case he wants to chime
> > in.
> > 
> > > > @@ -1038,16 +1038,11 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
> > > >  #define __KVM_HAVE_ARCH_VM_FREE
> > > >  void kvm_arch_free_vm(struct kvm *kvm);
> > > >  
> > > > -#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
> > > > -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
> > > > -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
> > > > -#else
> > > > -static inline int kvm_s390_pci_register_kvm(struct zpci_dev *dev,
> > > > -					    struct kvm *kvm)
> > > > -{
> > > > -	return -EPERM;
> > > > -}
> > > > -static inline void kvm_s390_pci_unregister_kvm(struct zpci_dev *dev) {}
> > > > -#endif
> > > > +struct kvm_register_hook {
> > > 
> > > Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.
> > 
> > Hmm, I guess one could re-use the same struct for another such KVM
> > dependency but I lean towards the same thinking as Matt, for now this
> > is for zpci so stay specific we can always generalize later.
> 
> Yes, let's keep this zpci-specific. 
> 
> > Nit: For me hook and register together sound a bit redudant, maybe
> > "zpci_kvm_register"? Also question for Matt as a native speaker, should
> > it rather be "registration" when used as a noun here?
> > 
> 
> Maybe just drop the 'register'.  If there is a need for a 3rd function later, for example, it might not be related to registration.

Yes, that sounds good and makes sense so "zpci_kvm_hook".

> 
> e.g. struct kvm_zpci_hook {
>    ...
> };
> 
> extern struct kvm_zpci_hook zpci_kvm;
> 
---8<---
> > > 
> > > > diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
> > > > new file mode 100644
> > > > index 000000000000..9d8799b72dbf
> > > > --- /dev/null
> > > > +++ b/arch/s390/pci/pci_kvm_hook.c
> > > > @@ -0,0 +1,11 @@
> > > > +// SPDX-License-Identifier: GPL-2.0-only
> > > > +/*
> > > > + * VFIO ZPCI devices support
> > > > + *
> > > > + * Copyright (C) IBM Corp. 2022.  All rights reserved.
> > > > + *	Author(s): Pierre Morel <pmorel@linux.ibm.com>
> > > > + */
> > > > +#include <linux/kvm_host.h>
> > > > +
> > > > +struct kvm_register_hook kvm_pci_hook;
> > > > +EXPORT_SYMBOL_GPL(kvm_pci_hook);
> > > 
> > > Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?
> > > 
> > > I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.
> > 
> > I'm fine with a separate file, pci.c is long enough as it is. I also
> > don't have a problem with having it maintained as part of S390 PCI but
> > logically I think it does fall more under arch/kvm/pci* so one could
> > argue it should be added in the MAINTAINERS file in that section.
> > If you change the struct name as I proposed above I would probably go
> > with "pci_kvm_register.c"
> 
> OK, no problem with me for a separate file then, or maintaining said file.  But I guess not pci_kvm_register.c per my comments above

Yes, let's go with pci_kvm_hook.c then

>

Re: [PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO

Posted by Pierre Morel 3 years, 7 months ago


On 8/18/22 15:33, Matthew Rosato wrote:
> On 8/18/22 6:23 AM, Pierre Morel wrote:
>> We have a cross dependency between KVM and VFIO.
> 
> maybe add something like 'when using s390 vfio_pci_zdev extensions for PCI passthrough'
> 
>> To be able to keep both subsystem modular we add a registering
>> hook inside the S390 core code.
>>
>> This fixes a build problem when VFIO is built-in and KVM is built
>> as a module or excluded.
> 
> s/or excluded//
> 
> There's no problem when KVM is excluded, that forces CONFIG_VFIO_PCI_ZDEV_KVM=n because of the 'depends on S390 && KVM'.

OK

> 
>>
>> Reported-by: Randy Dunlap <rdunlap@infradead.org>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
>> Cc: <stable@vger.kernel.org>
>> ---
>>   arch/s390/include/asm/kvm_host.h | 17 ++++++-----------
>>   arch/s390/kvm/pci.c              | 10 ++++++----
>>   arch/s390/pci/Makefile           |  2 ++
>>   arch/s390/pci/pci_kvm_hook.c     | 11 +++++++++++
>>   drivers/vfio/pci/vfio_pci_zdev.c |  8 ++++++--
>>   5 files changed, 31 insertions(+), 17 deletions(-)
>>   create mode 100644 arch/s390/pci/pci_kvm_hook.c
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index f39092e0ceaa..8312ed9d1937 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -1038,16 +1038,11 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
>>   #define __KVM_HAVE_ARCH_VM_FREE
>>   void kvm_arch_free_vm(struct kvm *kvm);
>>   
>> -#ifdef CONFIG_VFIO_PCI_ZDEV_KVM
>> -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm);
>> -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev);
>> -#else
>> -static inline int kvm_s390_pci_register_kvm(struct zpci_dev *dev,
>> -					    struct kvm *kvm)
>> -{
>> -	return -EPERM;
>> -}
>> -static inline void kvm_s390_pci_unregister_kvm(struct zpci_dev *dev) {}
>> -#endif
>> +struct kvm_register_hook {
> 
> Nit: zpci_kvm_register_hook ?  Just to make it clear it's for zpci.

OK


> 
>> +	int (*kvm_register)(void *opaque, struct kvm *kvm);
>> +	void (*kvm_unregister)(void *opaque);
>> +};
>> +
>> +extern struct kvm_register_hook kvm_pci_hook;
> 
> Nit: kvm_zpci_hook ?

OK too,

> 
>>   
>>   #endif
>> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
>> index 4946fb7757d6..e173fce64c4f 100644
>> --- a/arch/s390/kvm/pci.c
>> +++ b/arch/s390/kvm/pci.c
>> @@ -431,8 +431,9 @@ static void kvm_s390_pci_dev_release(struct zpci_dev *zdev)
>>    * available, enable them and let userspace indicate whether or not they will
>>    * be used (specify SHM bit to disable).
>>    */
>> -int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
>> +static int kvm_s390_pci_register_kvm(void *opaque, struct kvm *kvm)
>>   {
>> +	struct zpci_dev *zdev = opaque;
>>   	int rc;
>>   
>>   	if (!zdev)
>> @@ -510,10 +511,10 @@ int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm)
>>   	kvm_put_kvm(kvm);
>>   	return rc;
>>   }
>> -EXPORT_SYMBOL_GPL(kvm_s390_pci_register_kvm);
>>   
>> -void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
>> +static void kvm_s390_pci_unregister_kvm(void *opaque)
>>   {
>> +	struct zpci_dev *zdev = opaque;
>>   	struct kvm *kvm;
>>   
>>   	if (!zdev)
>> @@ -566,7 +567,6 @@ void kvm_s390_pci_unregister_kvm(struct zpci_dev *zdev)
>>   
>>   	kvm_put_kvm(kvm);
>>   }
>> -EXPORT_SYMBOL_GPL(kvm_s390_pci_unregister_kvm);
>>   
>>   void kvm_s390_pci_init_list(struct kvm *kvm)
>>   {
>> @@ -678,6 +678,8 @@ int kvm_s390_pci_init(void)
>>   
>>   	spin_lock_init(&aift->gait_lock);
>>   	mutex_init(&aift->aift_lock);
>> +	kvm_pci_hook.kvm_register = kvm_s390_pci_register_kvm;
>> +	kvm_pci_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
>>   
>>   	return 0;
>>   }
>> diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
>> index bf557a1b789c..c02dbfb415d9 100644
>> --- a/arch/s390/pci/Makefile
>> +++ b/arch/s390/pci/Makefile
>> @@ -7,3 +7,5 @@ obj-$(CONFIG_PCI)	+= pci.o pci_irq.o pci_dma.o pci_clp.o pci_sysfs.o \
>>   			   pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
>>   			   pci_bus.o
>>   obj-$(CONFIG_PCI_IOV)	+= pci_iov.o
>> +
>> +obj-y += pci_kvm_hook.o
> 
> I guess it doesn't harm anything to add this unconditionally, but I think it would also be OK to just include this in the CONFIG_PCI list - vfio_pci_zdev and arch/s390/kvm/pci all rely on CONFIG_PCI via CONFIG_VFIO_PCI_ZDEV_KVM which implies PCI via VFIO_PCI.

Right,CONFIG_PCI is a bool so we can put the hook in arch/s390/pci/pci.c 
and use a defined(CONFIG_PCI) to protect the initialization inside KVM.



> 
>> diff --git a/arch/s390/pci/pci_kvm_hook.c b/arch/s390/pci/pci_kvm_hook.c
>> new file mode 100644
>> index 000000000000..9d8799b72dbf
>> --- /dev/null
>> +++ b/arch/s390/pci/pci_kvm_hook.c
>> @@ -0,0 +1,11 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * VFIO ZPCI devices support
>> + *
>> + * Copyright (C) IBM Corp. 2022.  All rights reserved.
>> + *	Author(s): Pierre Morel <pmorel@linux.ibm.com>
>> + */
>> +#include <linux/kvm_host.h>
>> +
>> +struct kvm_register_hook kvm_pci_hook;
>> +EXPORT_SYMBOL_GPL(kvm_pci_hook);
> 
> Following the comments above, zpci_kvm_register_hook, kvm_zpci_hook ?

OK

> 
> I'm not sure if this really needs to be in a separate file or if it could just go into arch/s390/pci.c with the zpci_aipb -- If going the route of a separate file, up to Niklas whether he wants this under the S390 PCI maintainership or added to the list for s390 vfio-pci like arch/kvm/pci* and vfio_pci_zdev.

agreed no need for a separate file, it is much better.

> 
>> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
>> index e163aa9f6144..3b7a707e2fe5 100644
>> --- a/drivers/vfio/pci/vfio_pci_zdev.c
>> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
>> @@ -151,7 +151,10 @@ int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
>>   	if (!vdev->vdev.kvm)
>>   		return 0;
>>   
>> -	return kvm_s390_pci_register_kvm(zdev, vdev->vdev.kvm);
>> +	if (kvm_pci_hook.kvm_register)
>> +		return kvm_pci_hook.kvm_register(zdev, vdev->vdev.kvm);
>> +
>> +	return -ENOENT;
>>   }
>>   
>>   void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>> @@ -161,5 +164,6 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>>   	if (!zdev || !vdev->vdev.kvm)
>>   		return;
>>   
>> -	kvm_s390_pci_unregister_kvm(zdev);
>> +	if (kvm_pci_hook.kvm_unregister)
>> +		return kvm_pci_hook.kvm_unregister(zdev);
> 
> No need for the return here, this is a void function calling a void function.

right.

> 
> 
> Overall, this looks good to me and survives a series of compile and device passthrough tests on my end, just a matter of a few of these minor comments above.  Thanks for tackling this Pierre!
> 

Thanks,
Pierre


-- 
Pierre Morel
IBM Lab Boeblingen