On 2025/6/25 18:09, Jan Beulich wrote:
> On 25.06.2025 11:47, Chen, Jiqian wrote:
>> On 2025/6/25 17:15, Jan Beulich wrote:
>>> On 25.06.2025 09:16, Chen, Jiqian wrote:
>>>> On 2025/6/24 18:17, Jan Beulich wrote:
>>>>> On 24.06.2025 11:49, Chen, Jiqian wrote:
>>>>>> On 2025/6/18 22:45, Jan Beulich wrote:
>>>>>>> On 12.06.2025 11:29, Jiqian Chen wrote:
>>>>>>>> --- a/xen/drivers/vpci/msi.c
>>>>>>>> +++ b/xen/drivers/vpci/msi.c
>>>>>>>> @@ -193,6 +193,33 @@ static void cf_check mask_write(
>>>>>>>> msi->mask = val;
>>>>>>>> }
>>>>>>>>
>>>>>>>> +static int cf_check cleanup_msi(struct pci_dev *pdev)
>>>>>>>> +{
>>>>>>>> + int rc;
>>>>>>>> + unsigned int end, size;
>>>>>>>> + struct vpci *vpci = pdev->vpci;
>>>>>>>> + const unsigned int msi_pos = pdev->msi_pos;
>>>>>>>> + const unsigned int ctrl = msi_control_reg(msi_pos);
>>>>>>>> +
>>>>>>>> + if ( !msi_pos || !vpci->msi )
>>>>>>>> + return 0;
>>>>>>>> +
>>>>>>>> + if ( vpci->msi->masking )
>>>>>>>> + end = msi_pending_bits_reg(msi_pos, vpci->msi->address64);
>>>>>>>> + else
>>>>>>>> + end = msi_mask_bits_reg(msi_pos, vpci->msi->address64) - 2;
>>>>>>>> +
>>>>>>>> + size = end - ctrl;
>>>>>>>> +
>>>>>>>> + rc = vpci_remove_registers(vpci, ctrl, size);
>>>>>>>> + if ( rc )
>>>>>>>> + return rc;
>>>>>>>
>>>>>>> This is a difficult one: It's not a good idea to simply return here, yet
>>>>>>> at the same time the handling of the register we're unable to remove may
>>>>>>> still require e.g. ...
>>>>>>>
>>>>>>>> + XFREE(vpci->msi);
>>>>>>>
>>>>>>> ... this. There may therefore be more work required, such that in the
>>>>>>> end we're able to ...
>>>>>>>
>>>>>>>> + return vpci_add_register(pdev->vpci, vpci_hw_read16, NULL, ctrl,
>>>>>>>> 2, NULL);
>>>>>>>
>>>>>>> ... try this at least on a best effort basis.
>>>>>>>
>>>>>>> More generally: I don't think failure here (or in other .cleanup hook
>>>>>>> functions) may go entirely silently.
>>>>>> Does below meet your modification expectations?
>>>>>
>>>>> Not sure, sorry. By "more" I really meant "more" (which may just be code
>>>>> auditing, results of which would need writing down, but which may also
>>>>> involve further code changes; see below).
>>>>>
>>>>>> rc = vpci_remove_registers(vpci, ctrl, size);
>>>>>> if ( rc )
>>>>>> printk(XENLOG_ERR "%pd %pp: remove msi handlers fail rc=%d\n",
>>>>>> pdev->domain, &pdev->sbdf, rc);
>>>>>>
>>>>>> XFREE(vpci->msi);
>>>>>
>>>>> As I tried to indicate in my earlier reply, the freeing of this struct is
>>>>> safe only if the failure above would not leave any register handlers in
>>>>> place which still (without appropriate checking) use this struct.
>>>> Hmm, but all handlers added in init_msi() use this struct.
>>>> So it doesn't exist the case that when above unable to remove all handlers
>>>> and still require xfree this struct.
>>>
>>> Well, in the end you say in different words what I did say, if I understand
>>> correctly. There are several options how to deal with that. One might be to
>>> have those handlers recognize the lack of that pointer, and behave like ...
>>>
>>>>>> /*
>>>>>> * The driver may not traverse the capability list and think device
>>>>>> * supports MSI by default. So here let the control register of MSI
>>>>>> * be Read-Only is to ensure MSI disabled.
>>>>>> */
>>>>>> rc = vpci_add_register(vpci, vpci_hw_read16, NULL, ctrl, 2, NULL);
>>>
>>> ... what is tried to be put in place here (and like "no handler installed"
>>> for other registers).
>> According to your suggest. What I can think of is when
>> vpci_remove_registers() fails,
>> then lookup the MSI related handlers,
>
> What exactly does this mean? Aiui if vpci_remove_registers() ends up failing,
> it may be the lookup which is the problem. Which isn't why this wasn't what
> I suggested. Instead I suggested to make the respective handlers deal with
> the case of vpci->msi being NULL. Which of course in turn would require
> passing pdev->vpci to the respective vpci_add_register(), not pdev->vpci->msi.
Like below?
@@ -37,7 +42,13 @@ static uint32_t cf_check control_read(
static void cf_check control_write(
const struct pci_dev *pdev, unsigned int reg, uint32_t val, void *data)
{
- struct vpci_msi *msi = data;
+ const struct vpci *vpci = data;
+
+ if ( !vpci->msi )
+ return;
+
+ const struct vpci_msi *msi = vpci->msi;
+
unsigned int vectors = min_t(uint8_t,
1u << MASK_EXTR(val, PCI_MSI_FLAGS_QSIZE),
pdev->msi_maxvec);
@@ -239,7 +250,7 @@ static int cf_check init_msi(struct pci_dev *pdev)
return -ENOMEM;
ret = vpci_add_register(pdev->vpci, control_read, control_write,
- msi_control_reg(pos), 2, pdev->vpci->msi);
+ msi_control_reg(pos), 2, pdev->vpci);
>
>> and set the read/write hook to be vpci_ignored_read()/vpci_ignored_write(),
>
> But vpci_hw_read16() != vpci_ignored_read().
>
>> and set the private data to be NULL.
>> Is it acceptable?
>
> Altering already registered handler properties feels pretty fragile to me.
>
> Jan
--
Best regards,
Jiqian Chen.
