Subject: Re: [PATCH v7 27/50] powerpc/powernv: Dynamically release PEs

From: Alexey Kardashevskiy <[email-masked]>
Date: Tue, 24 Nov 2015 11:22:18 +1100

On 11/24/2015 10:06 AM, Gavin Shan wrote:
> On Wed, Nov 18, 2015 at 01:23:05PM +1100, Alexey Kardashevskiy wrote:
>> On 11/05/2015 12:12 AM, Gavin Shan wrote:
>>> This adds a reference count of PE, representing the number of PCI
>>> devices associated with the PE. The reference count is increased
>>> or decreased when PCI devices join or leave the PE. Once it becomes
>>> zero, the PE together with its used resources (IO, MMIO, DMA, PELTM,
>>> PELTV) are released to support PCI hot unplug.
>>
>>
>> The commit log suggest the patch only adds a counter, initializes it, and
>> replaces unconditional release of an object (in this case - PE) with the
>> conditional one. But it is more that that...
>>
>
> Yes, it's more than that as stated in the commit log.

More? The commit log only tells about reference counting.

>>> Signed-off-by: Gavin Shan <[email-masked]>
>>> ---
>>>   arch/powerpc/platforms/powernv/pci-ioda.c | 245 ++++++++++++++++++++++++++----
>>>   arch/powerpc/platforms/powernv/pci.h      |   1 +
>>>   2 files changed, 218 insertions(+), 28 deletions(-)
>>>
>>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>>> index 0bb0056..dcffce5 100644
>>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>>> @@ -129,6 +129,215 @@ static inline bool pnv_pci_is_mem_pref_64(unsigned long flags)
>>>   		(IORESOURCE_MEM_64 | IORESOURCE_PREFETCH));
>>>   }
>>>
>>> +static void pnv_pci_ioda1_release_dma_pe(struct pnv_ioda_pe *pe)
>>> +{
>>> +	struct pnv_phb *phb = pe->phb;
>>> +	struct iommu_table *tbl;
>>> +	int start, count, i;
>>> +	int64_t rc;
>>> +
>>> +	/* Search for the used DMA32 segments */
>>> +	start = -1;
>>> +	count = 0;
>>> +	for (i = 0; i < phb->ioda.dma32_count; i++) {
>>> +		if (phb->ioda.dma32_segmap[i] != pe->pe_number)
>>> +			continue;
>>> +
>>> +		count++;
>>> +		if (start < 0)
>>> +			start = i;
>>> +	}
>>> +
>>> +	if (!count)
>>> +		return;
>>
>>
>> imho checking pe->table_group.tables[0] != NULL is shorter than the loop above.
>>
>
> Will use it in next revision.
>
>>> +
>>> +	/* Unlink IOMMU table from group */
>>> +	tbl = pe->table_group.tables[0];
>>> +	pnv_pci_unlink_table_and_group(tbl, &pe->table_group);
>>> +	if (pe->table_group.group) {
>>> +		iommu_group_put(pe->table_group.group);
>>> +		WARN_ON(pe->table_group.group);
>>> +	}
>>> +
>>> +	/* Release IOMMU table */
>>> +	pnv_pci_ioda2_table_free_pages(tbl);
>>
>>
>> This is IODA2 helper with multilevel support, does IODA1 support multilevel
>> TCE tables? If not, it should WARN_ON on levels!=1.
>>
>> Another thing is you should first unprogram TVEs (via
>> opal_pci_map_pe_dma_window), then invalidate the cache (if required, not sure
>> if this is needed on IODA1), only then free the actual table.
>>
>>
>>> +	iommu_free_table(tbl, of_node_full_name(pci_bus_to_OF_node(pe->pbus)));
>>> +
>>> +	/* Disable TVE */
>>> +	for (i = start; i < start + count; i++) {
>>> +		rc = opal_pci_map_pe_dma_window(phb->opal_id, pe->pe_number,
>>> +						i, 0, 0ul, 0ul, 0ul);
>>> +		if (rc)
>>> +			pe_warn(pe, "Error %ld unmapping DMA32 seg#%d\n",
>>> +				rc, i);
>>> +
>>> +		phb->ioda.dma32_segmap[i] = IODA_INVALID_PE;
>>> +	}
>>
>>
>> You could implement pnv_pci_ioda1_unset_window/pnv_ioda1_table_free as
>> callbacks, change pnv_pci_ioda2_release_dma_pe() to use them (and rename it
>> to reflect that it supports IODA1 and IODA2).
>>
>>
>>> +}
>>> +
>>> +static unsigned int pnv_pci_ioda_pe_dma_weight(struct pnv_ioda_pe *pe);
>>> +static long pnv_pci_ioda2_unset_window(struct iommu_table_group *table_group,
>>> +		int num);
>>> +static void pnv_pci_ioda2_set_bypass(struct pnv_ioda_pe *pe, bool enable);
>>> +
>>> +static void pnv_pci_ioda2_release_dma_pe(struct pnv_ioda_pe *pe)
>>
>>
>> You moved this function and changed it, please do one thing at once (which is
>> "change", not "move").
>>
>>> +{
>>> +	struct iommu_table *tbl;
>>> +	unsigned int weight = pnv_pci_ioda_pe_dma_weight(pe);
>>> +	int64_t rc;
>>> +
>>> +	if (!weight)
>>> +		return;
>>
>>
>> Checking for pe->table_group.group is better because if we ever change the
>> logic of what gets included to an IOMMU group, we will have to do the change
>> where we add devices to a group but we won't have to touch releasing code.
>>
>>
>>> +
>>> +	tbl = pe->table_group.tables[0];
>>> +	rc = pnv_pci_ioda2_unset_window(&pe->table_group, 0);
>>> +	if (rc)
>>> +		pe_warn(pe, "OPAL error %ld release DMA window\n", rc);
>>> +
>>> +	pnv_pci_ioda2_set_bypass(pe, false);
>>> +	if (pe->table_group.group) {
>>> +		iommu_group_put(pe->table_group.group);
>>> +		WARN_ON(pe->table_group.group);
>>> +	}
>>> +
>>> +	pnv_pci_ioda2_table_free_pages(tbl);
>>> +	iommu_free_table(tbl, "pnv");
>>> +}
>>> +
>>> +static void pnv_ioda_release_dma_pe(struct pnv_ioda_pe *pe)
>>
>> Merge this into pnv_ioda_release_pe() - it is small and called just once.
>>
>>
>>> +{
>>> +	struct pnv_phb *phb = pe->phb;
>>> +
>>> +	switch (phb->type) {
>>> +	case PNV_PHB_IODA1:
>>> +		pnv_pci_ioda1_release_dma_pe(pe);
>>> +		break;
>>> +	case PNV_PHB_IODA2:
>>> +		pnv_pci_ioda2_release_dma_pe(pe);
>>> +		break;
>>> +	default:
>>> +		WARN_ON(1);
>>> +	}
>>> +}
>>> +
>>> +static void pnv_ioda_release_window(struct pnv_ioda_pe *pe, int win)
>>> +{
>>> +	struct pnv_phb *phb = pe->phb;
>>> +	int index, *segmap = NULL;
>>> +	int64_t rc;
>>> +
>>> +	switch (win) {
>>> +	case OPAL_IO_WINDOW_TYPE:
>>> +		segmap = phb->ioda.io_segmap;
>>> +		break;
>>> +	case OPAL_M32_WINDOW_TYPE:
>>> +		segmap = phb->ioda.m32_segmap;
>>> +		break;
>>> +	case OPAL_M64_WINDOW_TYPE:
>>> +		if (phb->type != PNV_PHB_IODA1)
>>> +			return;
>>> +		segmap = phb->ioda.m64_segmap;
>>> +		break;
>>> +	default:
>>> +		return;
>>
>> Unnecessary return.
>>
>>
>>> +	}
>>> +
>>> +	for (index = 0; index < phb->ioda.total_pe_num; index++) {
>>> +		if (segmap[index] != pe->pe_number)
>>> +			continue;
>>> +
>>> +		if (win == OPAL_M64_WINDOW_TYPE)
>>> +			rc = opal_pci_map_pe_mmio_window(phb->opal_id,
>>> +					phb->ioda.reserved_pe_idx, win,
>>> +					index / PNV_IODA1_M64_SEGS,
>>> +					index % PNV_IODA1_M64_SEGS);
>>> +		else
>>> +			rc = opal_pci_map_pe_mmio_window(phb->opal_id,
>>> +					phb->ioda.reserved_pe_idx, win,
>>> +					0, index);
>>> +
>>> +		if (rc != OPAL_SUCCESS)
>>> +			pe_warn(pe, "Error %ld unmapping (%d) segment#%d\n",
>>> +				rc, win, index);
>>> +
>>> +		segmap[index] = IODA_INVALID_PE;
>>> +	}
>>> +}
>>> +
>>> +static void pnv_ioda_release_pe_seg(struct pnv_ioda_pe *pe)
>>> +{
>>> +	struct pnv_phb *phb = pe->phb;
>>> +	int win;
>>> +
>>> +	for (win = OPAL_M32_WINDOW_TYPE; win <= OPAL_IO_WINDOW_TYPE; win++) {
>>> +		if (phb->type == PNV_PHB_IODA2 && win == OPAL_IO_WINDOW_TYPE)
>>> +			continue;
>>
>> Move this check to pnv_ioda_release_window() or move case(win ==
>> OPAL_M64_WINDOW_TYPE):if(phb->type != PNV_PHB_IODA1) from that function here.
>>
>>
>>> +
>>> +		pnv_ioda_release_window(pe, win);
>>> +	}
>>> +}
>>
>> This is shorter and cleaner:
>>
>>
>> static void pnv_ioda_release_window(struct pnv_ioda_pe *pe, int win, int
>> *segmap
>> {
>>         struct pnv_phb *phb = pe->phb;
>>         int index;
>>         int64_t rc;
>>
>>         for (index = 0; index < phb->ioda.total_pe_num; index++) {
>>                 if (segmap[index] != pe->pe_number)
>>                         continue;
>>
>>                 if (win == OPAL_M64_WINDOW_TYPE)
>>                         rc = opal_pci_map_pe_mmio_window(phb->opal_id,
>>                                         phb->ioda.reserved_pe_idx, win,
>>                                         index / PNV_IODA1_M64_SEGS,
>>                                         index % PNV_IODA1_M64_SEGS);
>>                 else
>>                         rc = opal_pci_map_pe_mmio_window(phb->opal_id,
>>                                         phb->ioda.reserved_pe_idx, win,
>>                                         0, index);
>>
>>                 if (rc != OPAL_SUCCESS)
>>                         pe_warn(pe, "Error %ld unmapping (%d) segment#%d\n",
>>                                 rc, win, index);
>>
>>                 segmap[index] = IODA_INVALID_PE;
>>         }
>> }
>>
>> static void pnv_ioda_release_pe_seg(struct pnv_ioda_pe *pe)
>> {
>>         pnv_ioda_release_window(pe, OPAL_M32_WINDOW_TYPE,
>> phb->ioda.m32_segmap);
>>         if (phb->type != PNV_PHB_IODA2)
>>                 pnv_ioda_release_window(pe, OPAL_IO_WINDOW_TYPE,
>>                                 phb->ioda.io_segmap);
>> 	else
>>                 pnv_ioda_release_window(pe, OPAL_M64_WINDOW_TYPE,
>>                                 phb->ioda.m64_segmap);
>> }
>>
>>
>> I'd actually merge pnv_ioda_release_pe_seg() into pnv_ioda_release_pe() as
>> well as it is also small and called once.
>>
>>
>>> +
>>> +static int pnv_ioda_deconfigure_pe(struct pnv_phb *phb,
>>> +				   struct pnv_ioda_pe *pe);
>>> +static void pnv_ioda_free_pe(struct pnv_ioda_pe *pe);
>>> +static void pnv_ioda_release_pe(struct pnv_ioda_pe *pe)
>>> +{
>>> +	struct pnv_ioda_pe *tmp, *slave;
>>> +
>>> +	/* Release slave PEs in compound PE */
>>> +	if (pe->flags & PNV_IODA_PE_MASTER) {
>>> +		list_for_each_entry_safe(slave, tmp, &pe->slaves, list)
>>> +			pnv_ioda_release_pe(slave);
>>> +	}
>>> +
>>> +	/* Remove the PE from the list */
>>> +	list_del(&pe->list);
>>> +
>>> +	/* Release resources */
>>> +	pnv_ioda_release_dma_pe(pe);
>>> +	pnv_ioda_release_pe_seg(pe);
>>> +	pnv_ioda_deconfigure_pe(pe->phb, pe);
>>> +
>>> +	pnv_ioda_free_pe(pe);
>>> +}
>>> +
>>> +static inline struct pnv_ioda_pe *pnv_ioda_pe_get(struct pnv_ioda_pe *pe)
>>> +{
>>> +	if (!pe)
>>> +		return NULL;
>>> +
>>> +	pe->device_count++;
>>> +	return pe;
>>> +}
>>> +
>>> +static inline void pnv_ioda_pe_put(struct pnv_ioda_pe *pe)
>>
>>
>> Merge this into pnv_pci_release_device() as it is small and called only once.
>>
>
> I don't think so. The functions pnv_ioda_pe_{get,put}() are paired. I think it's
> good enough to have separate function for the logic included in pnv_ioda_pe_put().

Ok. Another thing - just out of curiosity - is it possible and ok to have 
NULL in pe in these pnv_ioda_pe_put()/pnv_ioda_pe_get()? If it is NULL, 
does not this mean that something went wrong and we want WARN_ON or 
something like this?

>
>>> +{
>>> +	if (!pe)
>>> +		return;
>>> +
>>> +	pe->device_count--;
>>> +	WARN_ON(pe->device_count < 0);
>>> +	if (pe->device_count == 0)
>>> +		pnv_ioda_release_pe(pe);
>>> +}
>>> +
>>> +static void pnv_pci_release_device(struct pci_dev *pdev)
>>> +{
>>> +	struct pci_controller *hose = pci_bus_to_host(pdev->bus);
>>> +	struct pnv_phb *phb = hose->private_data;
>>> +	struct pci_dn *pdn = pci_get_pdn(pdev);
>>> +	struct pnv_ioda_pe *pe;
>>> +
>>> +	if (pdev->is_virtfn)
>>> +		return;
>>> +
>>> +	if (!pdn || pdn->pe_number == IODA_INVALID_PE)
>>> +		return;
>>> +
>>> +	pe = &phb->ioda.pe_array[pdn->pe_number];
>>> +	pnv_ioda_pe_put(pe);
>>> +}
>>> +
>>>   static struct pnv_ioda_pe *pnv_ioda_init_pe(struct pnv_phb *phb, int pe_no)
>>>   {
>>>   	phb->ioda.pe_array[pe_no].phb = phb;
>>> @@ -724,7 +933,6 @@ static int pnv_ioda_set_peltv(struct pnv_phb *phb,
>>>   	return 0;
>>>   }
>>>
>>> -#ifdef CONFIG_PCI_IOV
>>>   static int pnv_ioda_deconfigure_pe(struct pnv_phb *phb, struct pnv_ioda_pe *pe)
>>>   {
>>>   	struct pci_dev *parent;
>>> @@ -759,9 +967,11 @@ static int pnv_ioda_deconfigure_pe(struct pnv_phb *phb, struct pnv_ioda_pe *pe)
>>>   		}
>>>   		rid_end = pe->rid + (count << 8);
>>>   	} else {
>>> +#ifdef CONFIG_PCI_IOV
>>>   		if (pe->flags & PNV_IODA_PE_VF)
>>>   			parent = pe->parent_dev;
>>>   		else
>>> +#endif
>>>   			parent = pe->pdev->bus->self;
>>>   		bcomp = OpalPciBusAll;
>>>   		dcomp = OPAL_COMPARE_RID_DEVICE_NUMBER;
>>> @@ -799,11 +1009,12 @@ static int pnv_ioda_deconfigure_pe(struct pnv_phb *phb, struct pnv_ioda_pe *pe)
>>>
>>>   	pe->pbus = NULL;
>>>   	pe->pdev = NULL;
>>> +#ifdef CONFIG_PCI_IOV
>>>   	pe->parent_dev = NULL;
>>> +#endif
>>
>>
>> These #ifdef movements seem very much unrelated.
>>
>
> It's related: pnv_ioda_deconfigure_pe() was used for VF PE only. Now it's used by all
> types of PEs.

The commit log does not mention either VF or PF.

> pe->parent_dev is declared as below:
>
> #ifdef CONFIG_PCI_IOV
>          struct pci_dev          *parent_dev;
> #endif
>
>>
>>>
>>>   	return 0;
>>>   }
>>> -#endif /* CONFIG_PCI_IOV */
>>>
>>>   static int pnv_ioda_configure_pe(struct pnv_phb *phb, struct pnv_ioda_pe *pe)
>>>   {
>>> @@ -985,6 +1196,7 @@ static void pnv_ioda_setup_same_PE(struct pci_bus *bus, struct pnv_ioda_pe *pe)
>>>   			continue;
>>>
>>>   		pdn->pe_number = pe->pe_number;
>>> +		pnv_ioda_pe_get(pe);
>>>   		if ((pe->flags & PNV_IODA_PE_BUS_ALL) && dev->subordinate)
>>>   			pnv_ioda_setup_same_PE(dev->subordinate, pe);
>>>   	}
>>> @@ -1047,9 +1259,8 @@ static struct pnv_ioda_pe *pnv_ioda_setup_bus_PE(struct pci_bus *bus, bool all)
>>>   			bus->busn_res.start, pe->pe_number);
>>>
>>>   	if (pnv_ioda_configure_pe(phb, pe)) {
>>> -		/* XXX What do we do here ? */
>>> -		pnv_ioda_free_pe(pe);
>>>   		pe->pbus = NULL;
>>> +		pnv_ioda_release_pe(pe);
>>
>>
>> This is unrelated unexplained change.
>>
>
> Will drop it in next revision.
>
>>>   		return NULL;
>>>   	}
>>>
>>> @@ -1199,29 +1410,6 @@ m64_failed:
>>>   	return -EBUSY;
>>>   }
>>>
>>> -static long pnv_pci_ioda2_unset_window(struct iommu_table_group *table_group,
>>> -		int num);
>>> -static void pnv_pci_ioda2_set_bypass(struct pnv_ioda_pe *pe, bool enable);
>>> -
>>> -static void pnv_pci_ioda2_release_dma_pe(struct pci_dev *dev, struct pnv_ioda_pe *pe)
>>> -{
>>> -	struct iommu_table    *tbl;
>>> -	int64_t               rc;
>>> -
>>> -	tbl = pe->table_group.tables[0];
>>> -	rc = pnv_pci_ioda2_unset_window(&pe->table_group, 0);
>>> -	if (rc)
>>> -		pe_warn(pe, "OPAL error %ld release DMA window\n", rc);
>>> -
>>> -	pnv_pci_ioda2_set_bypass(pe, false);
>>> -	if (pe->table_group.group) {
>>> -		iommu_group_put(pe->table_group.group);
>>> -		BUG_ON(pe->table_group.group);
>>> -	}
>>> -	pnv_pci_ioda2_table_free_pages(tbl);
>>> -	iommu_free_table(tbl, of_node_full_name(dev->dev.of_node));
>>> -}
>>> -
>>>   static void pnv_ioda_release_vf_PE(struct pci_dev *pdev)
>>>   {
>>>   	struct pci_bus        *bus;
>>> @@ -1242,7 +1430,7 @@ static void pnv_ioda_release_vf_PE(struct pci_dev *pdev)
>>>   		if (pe->parent_dev != pdev)
>>>   			continue;
>>>
>>> -		pnv_pci_ioda2_release_dma_pe(pdev, pe);
>>> +		pnv_pci_ioda2_release_dma_pe(pe);
>>
>>
>> This is unrelated change.
>>
>
>
>>>
>>>   		/* Remove from list */
>>>   		mutex_lock(&phb->ioda.pe_list_mutex);
>>> @@ -3124,6 +3312,7 @@ static const struct pci_controller_ops pnv_pci_ioda_controller_ops = {
>>>   	.teardown_msi_irqs	= pnv_teardown_msi_irqs,
>>>   #endif
>>>   	.enable_device_hook	= pnv_pci_enable_device_hook,
>>> +	.release_device		= pnv_pci_release_device,
>>>   	.window_alignment	= pnv_pci_window_alignment,
>>>   	.setup_bridge		= pnv_pci_setup_bridge,
>>>   	.reset_secondary_bus	= pnv_pci_reset_secondary_bus,
>>> diff --git a/arch/powerpc/platforms/powernv/pci.h b/arch/powerpc/platforms/powernv/pci.h
>>> index ef5271a..3bb10de 100644
>>> --- a/arch/powerpc/platforms/powernv/pci.h
>>> +++ b/arch/powerpc/platforms/powernv/pci.h
>>> @@ -30,6 +30,7 @@ struct pnv_phb;
>>>   struct pnv_ioda_pe {
>>>   	unsigned long		flags;
>>>   	struct pnv_phb		*phb;
>>> +	int			device_count;
>>
>> Not atomic_t, no kref, no additional mutex, just "int"? Sure about it? If so,
>> put a note to the commit log about what provides a guarantee that there is no
>> race.
>>
>>
>
> It was a kref. Something you suggested on v5 as below:
>
> | You do not need kref here. You call kref_put() in a single location and can do
> | stuff directly, without kref. Just have an "unsigned int" counter and that's
> | it (it does not even have to be atomic if you do not have races but I am not
> | sure you do not).

Aaaaand I still do not see any mentioning why there is no race here.

> |
>
>>>
>>>   	/* A PE can be associated with a single device or an
>>>   	 * entire bus (& children). In the former case, pdev
>>>
>
> Thanks,
> Gavin
>
> --
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>

-- 
Alexey