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

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