Re: [PATCH v7 8/8] vpci/msix: Free MSIX resources when init_msix() fails

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Jul 04, 2025 at 03:08:03PM +0800, Jiqian Chen wrote:
> When init_msix() fails, current logic return fail and free MSIX-related
> resources in vpci_deassign_device(). But the previous new changes will
> hide MSIX capability and return success, it can't reach
> vpci_deassign_device() to remove resources if hiding success, so those
> resources must be removed in cleanup function of MSIX.
> 
> To do that, implement cleanup function for MSIX.
> 
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> ---
> cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
> ---
> v6->v7 changes:
> * Change the pointer parameter of cleanup_msix() to be const.
> * When vpci_remove_registers() in cleanup_msix() fails, not to return
>   directly, instead try to free msix and re-add ctrl handler.
> * Pass pdev->vpci into vpci_add_register() instead of pdev->vpci->msix in
>   init_msix() since we need that every handler realize that msix is NULL
>   when msix is freed but handlers are still in there.
> 
> v5->v6 changes:
> * Change the logic to add dummy handler when !vpci->msix in cleanup_msix().
> 
> v4->v5 changes:
> * Change definition "static void cleanup_msix" to "static int cf_check 
> cleanup_msix"
>   since cleanup hook is changed to be int.
> * Add a read-only register for MSIX Control Register in the end of 
> cleanup_msix().
> 
> v3->v4 changes:
> * Change function name from fini_msix() to cleanup_msix().
> * Change to use XFREE to free vpci->msix.
> * In cleanup function, change the sequence of check and remove action 
> according to
>   init_msix().
> 
> v2->v3 changes:
> * Remove unnecessary clean operations in fini_msix().
> 
> v1->v2 changes:
> new patch.
> 
> Best regards,
> Jiqian Chen.
> ---
>  xen/drivers/vpci/msix.c | 54 ++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 50 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/drivers/vpci/msix.c b/xen/drivers/vpci/msix.c
> index a1692b9d9f6a..114280337f3f 100644
> --- a/xen/drivers/vpci/msix.c
> +++ b/xen/drivers/vpci/msix.c
> @@ -36,7 +36,11 @@
>  static uint32_t cf_check control_read(
>      const struct pci_dev *pdev, unsigned int reg, void *data)
>  {
> -    const struct vpci_msix *msix = data;
> +    const struct vpci *vpci = data;
> +    const struct vpci_msix *msix = vpci->msix;
> +
> +    if ( !msix )
> +        return pci_conf_read16(pdev->sbdf, reg);
>  
>      return (msix->max_entries - 1) |
>             (msix->enabled ? PCI_MSIX_FLAGS_ENABLE : 0) |
> @@ -74,12 +78,16 @@ static void update_entry(struct vpci_msix_entry *entry,
>  static void cf_check control_write(
>      const struct pci_dev *pdev, unsigned int reg, uint32_t val, void *data)
>  {
> -    struct vpci_msix *msix = data;
> +    struct vpci *vpci = data;
> +    struct vpci_msix *msix = vpci->msix;
>      bool new_masked = val & PCI_MSIX_FLAGS_MASKALL;
>      bool new_enabled = val & PCI_MSIX_FLAGS_ENABLE;
>      unsigned int i;
>      int rc;
>  
> +    if ( !msix )
> +        return;
> +
>      if ( new_masked == msix->masked && new_enabled == msix->enabled )
>          return;
>  
> @@ -656,6 +664,44 @@ static int vpci_make_msix_hole(const struct pci_dev 
> *pdev)
>      return 0;
>  }
>  
> +static int cf_check cleanup_msix(const struct pci_dev *pdev)
> +{
> +    int rc;
> +    struct vpci *vpci = pdev->vpci;
> +    const unsigned int msix_pos = pdev->msix_pos;
> +
> +    if ( !msix_pos )
> +        return 0;
> +
> +    rc = vpci_remove_registers(vpci, msix_control_reg(msix_pos), 2);
> +    if ( rc )
> +        printk(XENLOG_WARNING "%pd %pp: fail to remove MSIX handlers 
> rc=%d\n",
> +               pdev->domain, &pdev->sbdf, rc);

The same comment as in the previous patch: vpci_remove_registers()
returning an error would likely imply memory corruption, and hence
it's best to just return error and avoid having to modify the
handlers.

Thanks, Roger.