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

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

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.

> 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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