Re: [PATCH v8 8/8] vpci/msix: Free MSIX resources when init_msix() fails

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2025/7/24 23:59, Roger Pau Monné wrote:
> On Thu, Jul 24, 2025 at 01:50:06PM +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.
> 
> The text here is a bit convoluted IMO.  It would be clearer as:
> 
> When MSI-X initialization fails vPCI will hide the capability, but
> remove of handlers and data won't be performed until the device is
> deassigned.  Introduce a MSI-X cleanup hook that will be called when
> initialization fails to cleanup MSI-X related hooks and free it's
> associated data.
> 
> As all supported capabilities have been switched to use the cleanup
> hooks call those from vpci_deassign_device() instead of open-code the
> capability specific cleanup in there.
Thanks, will change.

> 
> (see below for the reasoning behind the last paragrpah).
> 
>> To do that, implement cleanup function for MSIX.
>>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>> ---
>> cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
>> ---
>> v7->v8 changes:
>> * Given the code in vpci_remove_registers() an error in the removal of
>>   registers would likely imply memory corruption, at which point it's
>>   best to fully disable the device. So, Rollback the last two modifications 
>> of v7.
>>
>> 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 | 44 ++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 43 insertions(+), 1 deletion(-)
>>
>> diff --git a/xen/drivers/vpci/msix.c b/xen/drivers/vpci/msix.c
>> index eb3e7dcd1068..8ab159969da6 100644
>> --- a/xen/drivers/vpci/msix.c
>> +++ b/xen/drivers/vpci/msix.c
>> @@ -655,6 +655,48 @@ 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_ERR "%pd %pp: fail to remove MSIX handlers rc=%d\n",
>> +               pdev->domain, &pdev->sbdf, rc);
>> +        ASSERT_UNREACHABLE();
>> +        return rc;
>> +    }
>> +
>> +    if ( vpci->msix )
>> +    {
>> +        for ( unsigned int i = 0; i < ARRAY_SIZE(vpci->msix->table); i++ )
>> +            if ( vpci->msix->table[i] )
>> +                iounmap(vpci->msix->table[i]);
>> +
>> +        list_del(&vpci->msix->next);
Should I need to move this line above " for ( unsigned int i = 0; i < 
ARRAY_SIZE(vpci->msix->table); i++ )" ?
Because I noticed that is what it be in vpci_deassign_device.

>> +        XFREE(vpci->msix);
>> +    }
>> +
>> +    /*
>> +     * The driver may not traverse the capability list and think device
>> +     * supports MSIX by default. So here let the control register of MSIX
>> +     * be Read-Only is to ensure MSIX disabled.
>> +     */
>> +    rc = vpci_add_register(vpci, vpci_hw_read16, NULL,
>> +                           msix_control_reg(msix_pos), 2, NULL);
>> +    if ( rc )
>> +        printk(XENLOG_ERR "%pd %pp: fail to add MSIX ctrl handler rc=%d\n",
>> +               pdev->domain, &pdev->sbdf, rc);
>> +
>> +    return rc;
>> +}
>> +
>>  static int cf_check init_msix(struct pci_dev *pdev)
>>  {
>>      struct domain *d = pdev->domain;
>> @@ -714,7 +756,7 @@ static int cf_check init_msix(struct pci_dev *pdev)
>>  
>>      return rc;
>>  }
>> -REGISTER_VPCI_CAP(MSIX, init_msix, NULL);
>> +REGISTER_VPCI_CAP(MSIX, init_msix, cleanup_msix);
> 
> Don't you need to also call the cleanup hooks in
> vpci_deassign_device() and remove the open-coded cleaning of MSI-X
> done there?
Oh, will do.
How do I process the return value of cleanup_msix in vpci_deassign_device?
Just print an error when it fails and continue to do other deassign actions?

> 
> Otherwise the code here is duplicated with the code in
> vpci_deassign_device() for MSI-X cleanup (apart from it being a bit of
> a layering violation to open-code the MSI-X cleanup in there).
> 
> Thanks, Roger.

-- 
Best regards,
Jiqian Chen.