Re: [Xen-devel] [PATCH] fix MSI injection on Xen

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 2 Dec 2015, Michael S. Tsirkin wrote:
> On Wed, Dec 02, 2015 at 04:56:21PM +0000, Stefano Stabellini wrote:
> > On Xen MSIs can be remapped into pirqs, which are a type of event
> > channels. It's mostly for the benefit of PCI passthrough devices, to
> > avoid the overhead of interacting with the emulated lapic.
> > 
> > However remapping interrupts and MSIs is also supported for emulated
> > devices, such as the e1000 and virtio-net.
> > 
> > When an interrupt or an MSI is remapped into a pirq, masking and
> > unmasking is done by masking and unmasking the event channel. The
> > masking bit on the PCI config space or MSI-X table should be ignored,
> > but it isn't at the moment.
> > 
> > As a consequence emulated devices which use MSI or MSI-X, such as
> > virtio-net, don't work properly (the guest doesn't receive any
> > notifications). The mechanism was working properly when xen_apic was
> > introduced, but I haven't narrowed down which commit in particular is
> > causing the regression.
> > 
> > Fix the issue by ignoring the masking bit for MSI and MSI-X which have
> > been remapped into pirqs.
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > 
> 
> Is this a regression?
> If not I'd rather defer this until 2.6 when I can review properly.

Unfortunately it is a regression, but given that probably it has been
broken for multiple releases, I think you can wait until 2.6.


> > diff --git a/hw/pci/msi.c b/hw/pci/msi.c
> > index f9c0484..3998725 100644
> > --- a/hw/pci/msi.c
> > +++ b/hw/pci/msi.c
> > @@ -19,6 +19,7 @@
> >   */
> >  
> >  #include "hw/pci/msi.h"
> > +#include "hw/xen/xen.h"
> >  #include "qemu/range.h"
> >  
> >  /* PCI_MSI_ADDRESS_LO */
> > @@ -253,13 +254,19 @@ void msi_reset(PCIDevice *dev)
> >  static bool msi_is_masked(const PCIDevice *dev, unsigned int vector)
> >  {
> >      uint16_t flags = pci_get_word(dev->config + msi_flags_off(dev));
> > -    uint32_t mask;
> > +    uint32_t mask, data;
> > +    bool msi64bit = flags & PCI_MSI_FLAGS_64BIT;
> >      assert(vector < PCI_MSI_VECTORS_MAX);
> >  
> >      if (!(flags & PCI_MSI_FLAGS_MASKBIT)) {
> >          return false;
> >      }
> >  
> > +    data = pci_get_word(dev->config + msi_data_off(dev, msi64bit));
> > +    if (xen_is_pirq_msi(data)) {
> > +        return false;
> > +    }
> > +
> >      mask = pci_get_long(dev->config +
> >                          msi_mask_off(dev, flags & PCI_MSI_FLAGS_64BIT));
> >      return mask & (1U << vector);
> > diff --git a/hw/pci/msix.c b/hw/pci/msix.c
> > index 7716bf3..96281c2 100644
> > --- a/hw/pci/msix.c
> > +++ b/hw/pci/msix.c
> > @@ -18,6 +18,7 @@
> >  #include "hw/pci/msi.h"
> >  #include "hw/pci/msix.h"
> >  #include "hw/pci/pci.h"
> > +#include "hw/xen/xen.h"
> >  #include "qemu/range.h"
> >  
> >  #define MSIX_CAP_LENGTH 12
> > @@ -77,8 +78,15 @@ static void msix_clr_pending(PCIDevice *dev, int vector)
> >  
> >  static bool msix_vector_masked(PCIDevice *dev, unsigned int vector, bool 
> > fmask)
> >  {
> > -    unsigned offset = vector * PCI_MSIX_ENTRY_SIZE + 
> > PCI_MSIX_ENTRY_VECTOR_CTRL;
> > -    return fmask || dev->msix_table[offset] & PCI_MSIX_ENTRY_CTRL_MASKBIT;
> > +    unsigned offset = vector * PCI_MSIX_ENTRY_SIZE;
> > +    uint32_t *data = (uint32_t *)&dev->msix_table[offset + 
> > PCI_MSIX_ENTRY_DATA];
> > +    /* MSIs on Xen can be remapped into pirqs. In those cases, masking
> > +     * and unmasking go through the PV evtchn path. */
> > +    if (xen_is_pirq_msi(*data)) {
> > +        return false;
> > +    }
> > +    return fmask || dev->msix_table[offset + PCI_MSIX_ENTRY_VECTOR_CTRL] &
> > +        PCI_MSIX_ENTRY_CTRL_MASKBIT;
> >  }
> >  
> >  bool msix_is_masked(PCIDevice *dev, unsigned int vector)
> > diff --git a/hw/xen/xen_pt_msi.c b/hw/xen/xen_pt_msi.c
> > index 82de2bc..375707e 100644
> > --- a/hw/xen/xen_pt_msi.c
> > +++ b/hw/xen/xen_pt_msi.c
> > @@ -113,9 +113,7 @@ static int msi_msix_setup(XenPCIPassthroughState *s,
> >  
> >      assert((!is_msix && msix_entry == 0) || is_msix);
> >  
> > -    if (gvec == 0) {
> > -        /* if gvec is 0, the guest is asking for a particular pirq that
> > -         * is passed as dest_id */
> > +    if (xen_is_pirq_msi(data)) {
> >          *ppirq = msi_ext_dest_id(addr >> 32) | msi_dest_id(addr);
> >          if (!*ppirq) {
> >              /* this probably identifies an misconfiguration of the guest,
> > diff --git a/include/hw/xen/xen.h b/include/hw/xen/xen.h
> > index 4356af4..b15b2f5 100644
> > --- a/include/hw/xen/xen.h
> > +++ b/include/hw/xen/xen.h
> > @@ -32,6 +32,7 @@ int xen_pci_slot_get_pirq(PCIDevice *pci_dev, int 
> > irq_num);
> >  void xen_piix3_set_irq(void *opaque, int irq_num, int level);
> >  void xen_piix_pci_write_config_client(uint32_t address, uint32_t val, int 
> > len);
> >  void xen_hvm_inject_msi(uint64_t addr, uint32_t data);
> > +int xen_is_pirq_msi(uint32_t msi_data);
> >  
> >  qemu_irq *xen_interrupt_controller_init(void);
> >  
> > diff --git a/xen-hvm-stub.c b/xen-hvm-stub.c
> > index 46867d8..ce22a82 100644
> > --- a/xen-hvm-stub.c
> > +++ b/xen-hvm-stub.c
> > @@ -30,6 +30,11 @@ void xen_hvm_inject_msi(uint64_t addr, uint32_t data)
> >  {
> >  }
> >  
> > +int xen_is_pirq_msi(uint32_t msi_data)
> > +{
> > +    return 0;
> > +}
> > +
> >  void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size, MemoryRegion *mr)
> >  {
> >  }
> > diff --git a/xen-hvm.c b/xen-hvm.c
> > index 3371c4e..21dd301 100644
> > --- a/xen-hvm.c
> > +++ b/xen-hvm.c
> > @@ -12,6 +12,7 @@
> >  
> >  #include "hw/pci/pci.h"
> >  #include "hw/i386/pc.h"
> > +#include "hw/i386/apic-msidef.h"
> >  #include "hw/xen/xen_common.h"
> >  #include "hw/xen/xen_backend.h"
> >  #include "qmp-commands.h"
> > @@ -156,6 +157,14 @@ void xen_piix_pci_write_config_client(uint32_t 
> > address, uint32_t val, int len)
> >      }
> >  }
> >  
> > +int xen_is_pirq_msi(uint32_t msi_data)
> > +{
> > +    /* If vector is 0, the msi is remapped into a pirq, passed as
> > +     * dest_id.
> > +     */
> > +    return ((msi_data & MSI_DATA_VECTOR_MASK) >> MSI_DATA_VECTOR_SHIFT) == 
> > 0;
> > +}
> > +
> >  void xen_hvm_inject_msi(uint64_t addr, uint32_t data)
> >  {
> >      xen_xc_hvm_inject_msi(xen_xc, xen_domid, addr, data);
> 

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