Re: [PATCH V3 11/22] vfio-pci: refactor for cpr

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 21 May 2021 09:33:13 -0400
Steven Sistare <steven.sistare@oracle.com> wrote:

> On 5/19/2021 6:38 PM, Alex Williamson wrote:
> > On Fri,  7 May 2021 05:25:09 -0700
> > Steve Sistare <steven.sistare@oracle.com> wrote:
> >   
> >> Export vfio_address_spaces and vfio_listener_skipped_section.
> >> Add optional eventfd arg to vfio_add_kvm_msi_virq.
> >> Refactor vector use into a helper vfio_vector_init.
> >> All for use by cpr in a subsequent patch.  No functional change.
> >>
> >> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> >> ---
> >>  hw/vfio/common.c              |  4 ++--
> >>  hw/vfio/pci.c                 | 36 +++++++++++++++++++++++++-----------
> >>  include/hw/vfio/vfio-common.h |  3 +++
> >>  3 files changed, 30 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> >> index ae5654f..9220e64 100644
> >> --- a/hw/vfio/common.c
> >> +++ b/hw/vfio/common.c
> >> @@ -42,7 +42,7 @@
> >>  
> >>  VFIOGroupList vfio_group_list =
> >>      QLIST_HEAD_INITIALIZER(vfio_group_list);
> >> -static QLIST_HEAD(, VFIOAddressSpace) vfio_address_spaces =
> >> +VFIOAddressSpaceList vfio_address_spaces =
> >>      QLIST_HEAD_INITIALIZER(vfio_address_spaces);
> >>  
> >>  #ifdef CONFIG_KVM
> >> @@ -534,7 +534,7 @@ static int vfio_host_win_del(VFIOContainer *container, hwaddr min_iova,
> >>      return -1;
> >>  }
> >>  
> >> -static bool vfio_listener_skipped_section(MemoryRegionSection *section)
> >> +bool vfio_listener_skipped_section(MemoryRegionSection *section)
> >>  {
> >>      return (!memory_region_is_ram(section->mr) &&
> >>              !memory_region_is_iommu(section->mr)) ||
> >> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> >> index 5c65aa0..7a4fb6c 100644
> >> --- a/hw/vfio/pci.c
> >> +++ b/hw/vfio/pci.c
> >> @@ -411,7 +411,7 @@ static int vfio_enable_vectors(VFIOPCIDevice *vdev, bool msix)
> >>  }
> >>  
> >>  static void vfio_add_kvm_msi_virq(VFIOPCIDevice *vdev, VFIOMSIVector *vector,
> >> -                                  int vector_n, bool msix)
> >> +                                  int vector_n, bool msix, int eventfd)
> >>  {
> >>      int virq;
> >>  
> >> @@ -419,7 +419,9 @@ static void vfio_add_kvm_msi_virq(VFIOPCIDevice *vdev, VFIOMSIVector *vector,
> >>          return;
> >>      }
> >>  
> >> -    if (event_notifier_init(&vector->kvm_interrupt, 0)) {
> >> +    if (eventfd >= 0) {
> >> +        event_notifier_init_fd(&vector->kvm_interrupt, eventfd);
> >> +    } else if (event_notifier_init(&vector->kvm_interrupt, 0)) {
> >>          return;
> >>      }  
> > 
> > This seems very obfuscated.  The "active" arg of event_notifier_init()
> > just seems to preload the eventfd with a signal.  What does that have
> > to do with an eventfd arg to this function?  What if the first branch
> > returns failure?  
> 
> Perhaps you mis-read the code?  The function called in the first branch is different than
> the function called in the second branch.  And event_notifier_init_fd is void and never fails.
> 
> Eschew obfuscation.
> 
> Gesundheit.

D'oh!  I looked at that so many times trying to figure out what I was
missing and still didn't spot the "_fd" on the first function.  The
fact that @active is an int used as a bool in the non-fd version didn't
help.  Maybe we need our own wrapper just to spread the code out a
bit...

/* Create new or reuse existing eventfd */
static int vfio_event_notifier_init(EventNotifier *e, int fd)
{
    if (fd < 0) {
        return event_notifier_init(e, 0);
    }

    event_notifier_init_fd(e, fd);
    return 0;
}

Or I should just user bigger fonts, but that's somehow more apparent to
me and can be reused below.

> >> @@ -455,6 +457,22 @@ static void vfio_update_kvm_msi_virq(VFIOMSIVector *vector, MSIMessage msg,
> >>      kvm_irqchip_commit_routes(kvm_state);
> >>  }
> >>  
> >> +static void vfio_vector_init(VFIOPCIDevice *vdev, int nr, int eventfd)
> >> +{
> >> +    VFIOMSIVector *vector = &vdev->msi_vectors[nr];
> >> +    PCIDevice *pdev = &vdev->pdev;
> >> +
> >> +    vector->vdev = vdev;
> >> +    vector->virq = -1;
> >> +    if (eventfd >= 0) {
> >> +        event_notifier_init_fd(&vector->interrupt, eventfd);
> >> +    } else if (event_notifier_init(&vector->interrupt, 0)) {
> >> +        error_report("vfio: Error: event_notifier_init failed");
> >> +    }  
> > 
> > Gak, here's that same pattern.
> >   
> >> +    vector->use = true;
> >> +    msix_vector_use(pdev, nr);
> >> +}
> >> +
> >>  static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr,
> >>                                     MSIMessage *msg, IOHandler *handler)
> >>  {
> >> @@ -466,14 +484,10 @@ static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr,
> >>  
> >>      vector = &vdev->msi_vectors[nr];
> >>  
> >> +    vfio_vector_init(vdev, nr, -1);
> >> +
> >>      if (!vector->use) {
> >> -        vector->vdev = vdev;
> >> -        vector->virq = -1;
> >> -        if (event_notifier_init(&vector->interrupt, 0)) {
> >> -            error_report("vfio: Error: event_notifier_init failed");
> >> -        }
> >> -        vector->use = true;
> >> -        msix_vector_use(pdev, nr);
> >> +        vfio_vector_init(vdev, nr, -1);
> >>      }  
> > 
> > Huh?  That's not at all "no functional change".  Also the branch is
> > entirely dead code now.  
> 
> Good catch, thank you.  This is a rebase error.  The unconditional call to vfio_vector_init
> should not be there.  With that fix, we have:
> 
>     if (!vector->use) {
>         vfio_vector_init(vdev, nr, -1);
>     }
> 
> and there is no functional change; the actions performed in vfio_vector_init are identical to 
> those deleted here.

Yup.

> >>      qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
> >> @@ -491,7 +505,7 @@ static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr,
> >>          }
> >>      } else {
> >>          if (msg) {
> >> -            vfio_add_kvm_msi_virq(vdev, vector, nr, true);
> >> +            vfio_add_kvm_msi_virq(vdev, vector, nr, true, -1);
> >>          }
> >>      }
> >>  
> >> @@ -641,7 +655,7 @@ retry:
> >>           * Attempt to enable route through KVM irqchip,
> >>           * default to userspace handling if unavailable.
> >>           */
> >> -        vfio_add_kvm_msi_virq(vdev, vector, i, false);
> >> +        vfio_add_kvm_msi_virq(vdev, vector, i, false, -1);
> >>      }  
> > 
> > And then we're not really passing an eventfd anyway :-\  I'm so
> > confused...  
> 
> This patch just adds the eventfd arg.  The next few patches pass valid eventfd's from the
> cpr code paths.

Yeah, I couldn't put the pieces together though after repeatedly
misreading eventfd being used as a bool in event_notifier_init(), even
though -1 here should have clued me in too.  Thanks,

Alex