Re: [Qemu-devel] [PATCH v2] msix: don't mask already masked vectors on reset

[Marcel Apfelbaum <marcel@redhat.com>]

----- Original Message -----
> From: "Ladi Prosek" <lprosek@redhat.com>
> To: qemu-devel@nongnu.org
> Cc: marcel@redhat.com, geoff@hostfission.com, mst@redhat.com, "alex williamson" <alex.williamson@redhat.com>
> Sent: Friday, December 8, 2017 8:31:13 AM
> Subject: [PATCH v2] msix: don't mask already masked vectors on reset
> 
> msix_mask_all() is supposed to invoke the release vector notifier if the
> state of the
> respective vector changed from unmasked to masked. The way it's currently
> called from
> msix_reset(), though, may result in calling the release notifier even if the
> vector
> is already masked.
> 
> 1) msix_reset() clears out the msix_cap field and the msix_table.
> 2) msix_mask_all() runs with was_masked=false for all vectors because of 1),
> which
>    results in calling the release notifier on all vectors.
> 3) if msix_reset() is subsequently called again, it goes through the same
> steps and
>    calls the release notifier on all vectors again.
> 
> This commit moves msix_mask_all() up so it runs before the device state is
> lost. And
> it adds an assignment to msix_function_masked so that the device remembers
> that
> MSI-X is masked.
> 
> This is likely a low impact issue, found while debugging an already broken
> device. It
> is however easy to fix and the expectation that the use and release notifier
> invocations
> are always balanced is very natural.
> 
> Signed-off-by: Ladi Prosek <lprosek@redhat.com>
> ---
> 
> v1->v2:
> * fixed typo in commit message "or" -> "to" (Marcel)
> * directly set msix_function_masked to true instead of calling
>   msix_update_function_masked() (Marcel)
> 
> 
>  hw/pci/msix.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/pci/msix.c b/hw/pci/msix.c
> index c944c02135..d6a4dbdb6b 100644
> --- a/hw/pci/msix.c
> +++ b/hw/pci/msix.c
> @@ -500,11 +500,12 @@ void msix_reset(PCIDevice *dev)
>          return;
>      }
>      msix_clear_all_vectors(dev);
> +    msix_mask_all(dev, dev->msix_entries_nr);
>      dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] &=
>  	    ~dev->wmask[dev->msix_cap + MSIX_CONTROL_OFFSET];
>      memset(dev->msix_table, 0, dev->msix_entries_nr * PCI_MSIX_ENTRY_SIZE);
>      memset(dev->msix_pba, 0, QEMU_ALIGN_UP(dev->msix_entries_nr, 64) / 8);
> -    msix_mask_all(dev, dev->msix_entries_nr);
> +    dev->msix_function_masked = true;
>  }
>  
>  /* PCI spec suggests that devices make it possible for software to configure
> --
> 2.13.6
> 
> 

Thanks Ladi!

Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>