Re: [Qemu-devel] [PATCH for v1.0 1/3] msix: track function masked in pci device state

[Cam Macdonell]

Based on a git bisect, this patch breaks msi-x interrupt delivery in
the ivshmem device.

On Mon, Nov 21, 2011 at 9:57 AM, Michael S. Tsirkin <address@hidden> wrote:
> Only go over the table when function is masked.
> This is not really important for qemu.git but helps
> fix a bug in qemu-kvm.git.
>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
>  hw/msix.c |   21 ++++++++++++++-------
>  hw/pci.h  |    2 ++
>  2 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/hw/msix.c b/hw/msix.c
> index b15bafc..63b41b9 100644
> --- a/hw/msix.c
> +++ b/hw/msix.c
> @@ -79,6 +79,7 @@ static int msix_add_config(struct PCIDevice *pdev, unsigned 
> short nentries,
>     /* Make flags bit writable. */
>     pdev->wmask[config_offset + MSIX_CONTROL_OFFSET] |= MSIX_ENABLE_MASK |
>            MSIX_MASKALL_MASK;
> +    pdev->msix_function_masked = true;
>     return 0;

iiuc, this masks the msix by default.

>  }
>
> @@ -117,16 +118,11 @@ static void msix_clr_pending(PCIDevice *dev, int vector)
>     *msix_pending_byte(dev, vector) &= ~msix_pending_mask(vector);
>  }
>
> -static int msix_function_masked(PCIDevice *dev)
> -{
> -    return dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] & 
> MSIX_MASKALL_MASK;
> -}
> -
>  static int msix_is_masked(PCIDevice *dev, int vector)
>  {
>     unsigned offset =
>         vector * PCI_MSIX_ENTRY_SIZE + PCI_MSIX_ENTRY_VECTOR_CTRL;
> -    return msix_function_masked(dev) ||
> +    return dev->msix_function_masked ||
>           dev->msix_table_page[offset] & PCI_MSIX_ENTRY_CTRL_MASKBIT;
>  }
>
> @@ -138,24 +134,34 @@ static void msix_handle_mask_update(PCIDevice *dev, int 
> vector)
>     }
>  }
>
> +static void msix_update_function_masked(PCIDevice *dev)
> +{
> +    dev->msix_function_masked = !msix_enabled(dev) ||
> +        (dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] & 
> MSIX_MASKALL_MASK);
> +}
> +
>  /* Handle MSI-X capability config write. */
>  void msix_write_config(PCIDevice *dev, uint32_t addr,
>                        uint32_t val, int len)
>  {
>     unsigned enable_pos = dev->msix_cap + MSIX_CONTROL_OFFSET;
>     int vector;
> +    bool was_masked;
>
>     if (!range_covers_byte(addr, len, enable_pos)) {
>         return;
>     }
>
> +    was_masked = dev->msix_function_masked;
> +    msix_update_function_masked(dev);
> +
>     if (!msix_enabled(dev)) {
>         return;
>     }
>
>     pci_device_deassert_intx(dev);
>
> -    if (msix_function_masked(dev)) {
> +    if (dev->msix_function_masked == was_masked) {
>         return;
>     }

So I believe my bug is due to the fact the new logic included in this
patch requires msix_write_config() to be called to unmask the vectors.
 Virtio-pci calls msix_write_config(), but ivshmem does not (nor does
PCIe so I'm not sure if it's also affected).

I haven't been able to fix the bug yet, but I wanted to make sure I
was looking in the correct place.  Any help of further explanation of
this patch would be greatly appreciated.

Sincerely,
Cam

>
> @@ -300,6 +306,7 @@ void msix_load(PCIDevice *dev, QEMUFile *f)
>     msix_free_irq_entries(dev);
>     qemu_get_buffer(f, dev->msix_table_page, n * PCI_MSIX_ENTRY_SIZE);
>     qemu_get_buffer(f, dev->msix_table_page + MSIX_PAGE_PENDING, (n + 7) / 8);
> +    msix_update_function_masked(dev);
>  }
>
>  /* Does device support MSI-X? */
> diff --git a/hw/pci.h b/hw/pci.h
> index 4b2e785..625e717 100644
> --- a/hw/pci.h
> +++ b/hw/pci.h
> @@ -178,6 +178,8 @@ struct PCIDevice {
>     unsigned *msix_entry_used;
>     /* Region including the MSI-X table */
>     uint32_t msix_bar_size;
> +    /* MSIX function mask set or MSIX disabled */
> +    bool msix_function_masked;
>     /* Version id needed for VMState */
>     int32_t version_id;
>
> --
> 1.7.5.53.gc233e
>
>