RE: [v2 17/25] KVM: kvm-vfio: User API for VT-d Posted-Interrupts

From: Wu, Feng
Date: Thu Dec 11 2014 - 00:55:29 EST

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In reply to: Wu, Feng: "RE: [v2 17/25] KVM: kvm-vfio: User API for VT-d Posted-Interrupts"
Next in thread: Alex Williamson: "Re: [v2 17/25] KVM: kvm-vfio: User API for VT-d Posted-Interrupts"
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> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: Monday, December 08, 2014 1:21 PM
> To: Wu, Feng
> Cc: Eric Auger; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx;
> x86@xxxxxxxxxx; gleb@xxxxxxxxxx; pbonzini@xxxxxxxxxx;
> dwmw2@xxxxxxxxxxxxx; joro@xxxxxxxxxx; jiang.liu@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx
> Subject: Re: [v2 17/25] KVM: kvm-vfio: User API for VT-d Posted-Interrupts
>
> On Mon, 2014-12-08 at 04:58 +0000, Wu, Feng wrote:
> >
> > > -----Original Message-----
> > > From: kvm-owner@xxxxxxxxxxxxxxx [mailto:kvm-owner@xxxxxxxxxxxxxxx]
> On
> > > Behalf Of Eric Auger
> > > Sent: Thursday, December 04, 2014 10:05 PM
> > > To: Wu, Feng; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx;
> > > x86@xxxxxxxxxx; gleb@xxxxxxxxxx; pbonzini@xxxxxxxxxx;
> > > dwmw2@xxxxxxxxxxxxx; joro@xxxxxxxxxx; alex.williamson@xxxxxxxxxx;
> > > jiang.liu@xxxxxxxxxxxxxxx
> > > Cc: linux-kernel@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> > > kvm@xxxxxxxxxxxxxxx
> > > Subject: Re: [v2 17/25] KVM: kvm-vfio: User API for VT-d Posted-Interrupts
> > >
> > > Hi Feng,
> > > On 12/03/2014 08:39 AM, Feng Wu wrote:
> > > > This patch adds and documents a new attribute
> > > > KVM_DEV_VFIO_DEVICE_POSTING_IRQ in KVM_DEV_VFIO_DEVICE
> group.
> > > > This new attribute is used for VT-d Posted-Interrupts.
> > > >
> > > > When guest OS changes the interrupt configuration for an
> > > > assigned device, such as, MSI/MSIx data/address fields,
> > > > QEMU will use this IRQ attribute to tell KVM to update the
> > > > related IRTE according the VT-d Posted-Interrrupts Specification,
> > > > such as, the guest vector should be updated in the related IRTE.
> > > >
> > > > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > > > ---
> > > > Documentation/virtual/kvm/devices/vfio.txt | 9 +++++++++
> > > > include/uapi/linux/kvm.h | 10 ++++++++++
> > > > 2 files changed, 19 insertions(+), 0 deletions(-)
> > > >
> > > > diff --git a/Documentation/virtual/kvm/devices/vfio.txt
> > > b/Documentation/virtual/kvm/devices/vfio.txt
> > > > index f7aff29..41e12b7 100644
> > > > --- a/Documentation/virtual/kvm/devices/vfio.txt
> > > > +++ b/Documentation/virtual/kvm/devices/vfio.txt
> > > > @@ -42,3 +42,12 @@ activated before VFIO_DEVICE_SET_IRQS has
> been
> > > called to trigger the IRQ
> > > > or associate an eventfd to it. Unforwarding can only be called while the
> > > > signaling has been disabled with VFIO_DEVICE_SET_IRQS. If this
> condition
> > > is
> > > > not satisfied, the command returns an -EBUSY.
> > > > +
> > > > + KVM_DEV_VFIO_DEVICE_POSTING_IRQ: Use posted interrtups
> > > mechanism to post
> > > typo
> > > > + the IRQ to guests.
> > > > +For this attribute, kvm_device_attr.addr points to a kvm_vfio_dev_irq
> > > struct.
> > > > +
> > > > +When guest OS changes the interrupt configuration for an assigned
> device,
> > > > +such as, MSI/MSIx data/address fields, QEMU will use this IRQ attribute
> > > > +to tell KVM to update the related IRTE according the VT-d
> > > Posted-Interrrupts
> > > > +Specification, such as, the guest vector should be updated in the related
> > > IRTE.
> > > For my curiosity are there any restrictions about the instant at which
> > > the change can be done?
> > > I do not get here how you deactivate the posting?
> >
> > The current method is if the hardware supports interrupts posting, we will
> > use it instead of interrupts remapping, since it has good performance. Why
> > do I need deactivate interrupts posting?
> >
> > Here is the reply to Alex for the same question:
> > "In fact, I don't think we need to stop the posted-interrupts. For setting
> > posted interrupts, we update the related IRTE according to the new
> > format. If the guest reboots, or unload the drivers, or some other
> > operations, the msi/msix will be disabled first, in this path, the irq
> > will be disabled the related IRTE is not used anymore."
>
> Right, and I'm still not sure I agree with that reasoning. We need to
> build the kernel interface to be generic, not tailored for a specific
> userspace. I don't really feel comfortable having something that can't
> be disabled via a similar path to it being enabled. For instance, what
> about a dynamic debug interface where we want to enable tracing and see
> each interrupt injected into the guest. At that point we'd want to
> disabled posted interrupts and direct KVM injection and route via QEMU.
> Thanks,
>
> Alex

I am not quite understand why we need to debug the software
delivery path for interrupt when PI is used, in this case, the software
injection code will have no chance to execute. If we don't want the use
PI, we can disable it from kernel command line.

Thanks,
Feng

>
> > > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > > > index a269a42..7d98650 100644
> > > > --- a/include/uapi/linux/kvm.h
> > > > +++ b/include/uapi/linux/kvm.h
> > > > @@ -949,6 +949,7 @@ struct kvm_device_attr {
> > > > #define KVM_DEV_VFIO_DEVICE 2
> > > > #define KVM_DEV_VFIO_DEVICE_FORWARD_IRQ 1
> > > > #define KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ 2
> > > > +#define KVM_DEV_VFIO_DEVICE_POSTING_IRQ 3
> > > Maybe we should align our naming verb vs verbing here?
> > > Best Regards
> > > Eric
> >
> > No problem, I will align my patch in the next version. Thanks!
> >
> > Thanks,
> > Feng
> >
> > > >
> > > > enum kvm_device_type {
> > > > KVM_DEV_TYPE_FSL_MPIC_20 = 1,
> > > > @@ -973,6 +974,15 @@ struct kvm_arch_forwarded_irq {
> > > > __u32 gsi; /* gsi, ie. virtual IRQ number */
> > > > };
> > > >
> > > > +struct kvm_vfio_dev_irq {
> > > > + __u32 argsz;
> > > > + __u32 fd; /* file descriptor of the VFIO device */
> > > > + __u32 index; /* VFIO device IRQ index */
> > > > + __u32 start;
> > > > + __u32 count;
> > > > + __u32 gsi[]; /* gsi, ie. virtual IRQ number */
> > > > +};
> > > > +
> > > > /*
> > > > * ioctls for VM fds
> > > > */
> > > >
> > >
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe kvm" in
> > > the body of a message to majordomo@xxxxxxxxxxxxxxx
> > > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > --
> > To unsubscribe from this list: send the line "unsubscribe kvm" in
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>
>

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Next message: Michael Ellerman: "Re: [GIT PULL] ipmi driver updates"
Previous message: Liu Ying: "Re: [PATCH RFC 04/15] drm/dsi: Do not add DSI devices for the child nodes with input-port property"
In reply to: Wu, Feng: "RE: [v2 17/25] KVM: kvm-vfio: User API for VT-d Posted-Interrupts"
Next in thread: Alex Williamson: "Re: [v2 17/25] KVM: kvm-vfio: User API for VT-d Posted-Interrupts"
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