On 3/14/23 3:08 AM, Ganapatrao Kulkarni wrote:
>
>
> On 14-03-2023 04:00 am, Sathyanarayanan Kuppuswamy wrote:
>> Hi Kulkarni,
>>
>> On 3/13/23 2:12 PM, Bjorn Helgaas wrote:
>>> On Mon, Feb 27, 2023 at 08:21:36PM -0800, Ganapatrao Kulkarni wrote:
>>>> As per PCI specification (PCI Express Base Specification Revision
>>>> 6.0, Section 10.5) both PF and VFs of a PCI EP are permitted to be enabled
>>>> independently for ATS capability, however the STU(Smallest Translation
>>>> Unit) is shared between PF and VFs. For VFs, it is hardwired to Zero and
>>>> the associated PF's value applies to VFs.
>>>>
>>>> In the current code, the STU is being configured while enabling the PF ATS.
>>>> Hence, it is not able to enable ATS for VFs, if it is not enabled on the
>>>> associated PF already.
>>>>
>>>> Adding a function pci_ats_stu_configure(), which can be called to
>>>> configure the STU during PF enumeration.
>>>> Latter enumerations of VFs can successfully enable ATS independently.
>>>
>>> s/STU(Smallest/STU (Smallest/ (add space before paren)
>>> s/Adding a function pci_ats_stu_configure()/Add pci_ats_stu_configure()/
>>> s/Latter/Subsequent/
>>>
>>> Add blank line between paragraphs (it looks like "Latter enumerations"
>>> is intended to start a new paragraph).
>>>
>>>> Signed-off-by: Ganapatrao Kulkarni <gankulkarni@xxxxxxxxxxxxxxxxxxxxxx>
>>>
>>> Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>>>
>>> Given an ack for the IOMMU patch, I'd be happy to merge both (and I
>>> can do the commit log tweaks); just let me know.
>>>
>>> One comment/question below.
>>>
>>>> ---
>>>> drivers/pci/ats.c | 33 +++++++++++++++++++++++++++++++--
>>>> include/linux/pci-ats.h | 3 +++
>>>> 2 files changed, 34 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
>>>> index f9cc2e10b676..1611bfa1d5da 100644
>>>> --- a/drivers/pci/ats.c
>>>> +++ b/drivers/pci/ats.c
>>>> @@ -46,6 +46,35 @@ bool pci_ats_supported(struct pci_dev *dev)
>>>> }
>>>> EXPORT_SYMBOL_GPL(pci_ats_supported);
>>>> +/**
>>>> + * pci_ats_stu_configure - Configure STU of a PF.
>>>> + * @dev: the PCI device
>>>> + * @ps: the IOMMU page shift
>>>> + *
>>>> + * Returns 0 on success, or negative on failure.
>>>> + */
>>>> +int pci_ats_stu_configure(struct pci_dev *dev, int ps)
>>>> +{
>>>> + u16 ctrl;
>>>> +
>>>> + if (dev->ats_enabled || dev->is_virtfn)
>>>> + return 0;
>>>
>>> I might return an error for the VF case on the assumption that it's
>>> likely an error in the caller. I guess one could argue that it
>>> simplifies the caller if it doesn't have to check for PF vs VF. But
>>> the fact that STU is shared between PF and VFs is an important part of
>>> understanding how ATS works, so the caller should be aware of the
>>> distinction anyway.
>>
>> I have already asked this question. But let me repeat it.
>>
>> We don't have any checks for the PF case here. That means you can re-configure
>> the STU as many times as you want until ATS is enabled in PF. So, if there are
>> active VFs which uses this STU, can PF re-configure the STU at will?
>>
>
> IMO, Since STU is shared, programming it multiple times is not expected from callers code do it, however we can add below check to allow to program STU once from a PF.
>
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index 1611bfa1d5da..f7bb01068e18 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -60,6 +60,10 @@ int pci_ats_stu_configure(struct pci_dev *dev, int ps)
> if (dev->ats_enabled || dev->is_virtfn)
> return 0;
>
> + /* Configured already */
> + if (dev->ats_stu)
> + return 0;
> +
Theoretically, you can re-configure STU as long as no one is using it. Instead of this check, is
there a way to check whether there are active VMs which enables ATS?
> if (!pci_ats_supported(dev))
> return -EINVAL;
>>>
>>>> +
>>>> + if (!pci_ats_supported(dev))
>>>> + return -EINVAL;
>>>> +
>>>> + if (ps < PCI_ATS_MIN_STU)
>>>> + return -EINVAL;
>>>> +
>>>> + dev->ats_stu = ps;
>>>> + pci_read_config_word(dev, dev->ats_cap + PCI_ATS_CTRL, &ctrl);
>>>> + ctrl |= PCI_ATS_CTRL_STU(dev->ats_stu - PCI_ATS_MIN_STU);
>>>> + pci_write_config_word(dev, dev->ats_cap + PCI_ATS_CTRL, ctrl);
>>>> +
>>>> + return 0;
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(pci_ats_stu_configure);
>>>> +
>>>> /**
>>>> * pci_enable_ats - enable the ATS capability
>>>> * @dev: the PCI device
>>>> @@ -68,8 +97,8 @@ int pci_enable_ats(struct pci_dev *dev, int ps)
>>>> return -EINVAL;
>>>> /*
>>>> - * Note that enabling ATS on a VF fails unless it's already enabled
>>>> - * with the same STU on the PF.
>>>> + * Note that enabling ATS on a VF fails unless it's already
>>>> + * configured with the same STU on the PF.
>>>> */
>>>> ctrl = PCI_ATS_CTRL_ENABLE;
>>>> if (dev->is_virtfn) {
>>>> diff --git a/include/linux/pci-ats.h b/include/linux/pci-ats.h
>>>> index df54cd5b15db..7d62a92aaf23 100644
>>>> --- a/include/linux/pci-ats.h
>>>> +++ b/include/linux/pci-ats.h
>>>> @@ -8,6 +8,7 @@
>>>> /* Address Translation Service */
>>>> bool pci_ats_supported(struct pci_dev *dev);
>>>> int pci_enable_ats(struct pci_dev *dev, int ps);
>>>> +int pci_ats_stu_configure(struct pci_dev *dev, int ps);
>>>> void pci_disable_ats(struct pci_dev *dev);
>>>> int pci_ats_queue_depth(struct pci_dev *dev);
>>>> int pci_ats_page_aligned(struct pci_dev *dev);
>>>> @@ -16,6 +17,8 @@ static inline bool pci_ats_supported(struct pci_dev *d)
>>>> { return false; }
>>>> static inline int pci_enable_ats(struct pci_dev *d, int ps)
>>>> { return -ENODEV; }
>>>> +static inline int pci_ats_stu_configure(struct pci_dev *d, int ps)
>>>> +{ return -ENODEV; }
>>>> static inline void pci_disable_ats(struct pci_dev *d) { }
>>>> static inline int pci_ats_queue_depth(struct pci_dev *d)
>>>> { return -ENODEV; }
>>>> --
>>>> 2.38.1
>>>>
>>>>
>>>> _______________________________________________
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>>>> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
>
> Thanks,
> Ganapat
>
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
