Re: [PATCH] KVM: s390: pci: Hook to access KVM lowlevel from VFIO
From: Pierre Morel
Date: Thu Aug 18 2022 - 10:07:00 EST
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@xxxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
Fixes: 09340b2fca007 ("KVM: s390: pci: add routines to start/stop inter..")
Cc: <stable@xxxxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxx>
+ */
+#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