qemu-devel.nongnu.org archive mirror
 help / color / mirror / Atom feed
From: Alex Williamson <alex.williamson@redhat.com>
To: aliguori@us.ibm.com
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, qemu-stable@nongnu.org
Subject: [Qemu-devel] [PATCH 1/2] vfio-pci: Make host MSI-X enable track guest
Date: Wed, 09 Jan 2013 12:19:29 -0700	[thread overview]
Message-ID: <20130109191929.906.36284.stgit@bling.home> (raw)
In-Reply-To: <20130109191807.906.7307.stgit@bling.home>

Guests typically enable MSI-X with all of the vectors in the MSI-X
vector table masked.  Only when the vector is enabled does the vector
get unmasked, resulting in a vector_use callback.  These two points,
enable and unmask, correspond to pci_enable_msix() and request_irq()
for Linux guests.  Some drivers rely on VF/PF or PF/fw communication
channels that expect the physical state of the device to match the
guest visible state of the device.  They don't appreciate lazily
enabling MSI-X on the physical device.

To solve this, enable MSI-X with a single vector when the MSI-X
capability is enabled and immediate disable the vector.  This leaves
the physical device in exactly the same state between host and guest.
Furthermore, the brief gap where we enable vector 0, it fires into
userspace, not KVM, so the guest doesn't get spurious interrupts.
Ideally we could call VFIO_DEVICE_SET_IRQS with the right parameters
to enable MSI-X with zero vectors, but this will currently return an
error as the Linux MSI-X interfaces do not allow it.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Cc: qemu-stable@nongnu.org
---
 hw/vfio_pci.c |   30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/hw/vfio_pci.c b/hw/vfio_pci.c
index 28c8303..8ec1faf 100644
--- a/hw/vfio_pci.c
+++ b/hw/vfio_pci.c
@@ -562,8 +562,8 @@ static int vfio_enable_vectors(VFIODevice *vdev, bool msix)
     return ret;
 }
 
-static int vfio_msix_vector_use(PCIDevice *pdev,
-                                unsigned int nr, MSIMessage msg)
+static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr,
+                                   MSIMessage *msg, IOHandler *handler)
 {
     VFIODevice *vdev = DO_UPCAST(VFIODevice, pdev, pdev);
     VFIOMSIVector *vector;
@@ -587,7 +587,7 @@ static int vfio_msix_vector_use(PCIDevice *pdev,
      * Attempt to enable route through KVM irqchip,
      * default to userspace handling if unavailable.
      */
-    vector->virq = kvm_irqchip_add_msi_route(kvm_state, msg);
+    vector->virq = msg ? kvm_irqchip_add_msi_route(kvm_state, *msg) : -1;
     if (vector->virq < 0 ||
         kvm_irqchip_add_irqfd_notifier(kvm_state, &vector->interrupt,
                                        vector->virq) < 0) {
@@ -596,7 +596,7 @@ static int vfio_msix_vector_use(PCIDevice *pdev,
             vector->virq = -1;
         }
         qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
-                            vfio_msi_interrupt, NULL, vector);
+                            handler, NULL, vector);
     }
 
     /*
@@ -639,6 +639,12 @@ static int vfio_msix_vector_use(PCIDevice *pdev,
     return 0;
 }
 
+static int vfio_msix_vector_use(PCIDevice *pdev,
+                                unsigned int nr, MSIMessage msg)
+{
+    return vfio_msix_vector_do_use(pdev, nr, &msg, vfio_msi_interrupt);
+}
+
 static void vfio_msix_vector_release(PCIDevice *pdev, unsigned int nr)
 {
     VFIODevice *vdev = DO_UPCAST(VFIODevice, pdev, pdev);
@@ -697,6 +703,22 @@ static void vfio_enable_msix(VFIODevice *vdev)
 
     vdev->interrupt = VFIO_INT_MSIX;
 
+    /*
+     * Some communication channels between VF & PF or PF & fw rely on the
+     * physical state of the device and expect that enabling MSI-X from the
+     * guest enables the same on the host.  When our guest is Linux, the
+     * guest driver call to pci_enable_msix() sets the enabling bit in the
+     * MSI-X capability, but leaves the vector table masked.  We therefore
+     * can't rely on a vector_use callback (from request_irq() in the guest)
+     * to switch the physical device into MSI-X mode because that may come a
+     * long time after pci_enable_msix().  This code enables vector 0 with
+     * triggering to userspace, then immediately release the vector, leaving
+     * the physical device with no vectors enabled, but MSI-X enabled, just
+     * like the guest view.
+     */
+    vfio_msix_vector_do_use(&vdev->pdev, 0, NULL, NULL);
+    vfio_msix_vector_release(&vdev->pdev, 0);
+
     if (msix_set_vector_notifiers(&vdev->pdev, vfio_msix_vector_use,
                                   vfio_msix_vector_release, NULL)) {
         error_report("vfio: msix_set_vector_notifiers failed\n");

  reply	other threads:[~2013-01-09 20:46 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-09 19:19 [Qemu-devel] [PULL 0/2] vfio-pci: Fixes for 1.4 & stable Alex Williamson
2013-01-09 19:19 ` Alex Williamson [this message]
2013-01-09 19:19 ` [Qemu-devel] [PATCH 2/2] vfio-pci: Loosen sanity checks to allow future features Alex Williamson
2013-01-10 20:57 ` [Qemu-devel] [PULL 0/2] vfio-pci: Fixes for 1.4 & stable Anthony Liguori

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20130109191929.906.36284.stgit@bling.home \
    --to=alex.williamson@redhat.com \
    --cc=aliguori@us.ibm.com \
    --cc=kvm@vger.kernel.org \
    --cc=qemu-devel@nongnu.org \
    --cc=qemu-stable@nongnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).