Subject: Re: [PATCH V6 1/6] powerpc/powernv: don't enable SRIOV when VF BAR has non 64bit-prefetchable BAR

From: Wei Yang <[email-masked]>
Date: Wed, 21 Oct 2015 14:38:55 +0800

On Wed, Oct 21, 2015 at 11:44:26AM +1100, Gavin Shan wrote:
>On Tue, Oct 20, 2015 at 05:03:00PM +0800, Wei Yang wrote:
>>On PHB_IODA2, we enable SRIOV devices by mapping IOV BAR with M64 BARs. If
>    ^^^^^^^^^
>
>s/PHB_IODA2/PHB3 or s/PHB_IODA2/IODA2 PHB
>
>>a SRIOV device's IOV BAR is not 64bit-prefetchable, this is not assigned
>>from 64bit prefetchable window, which means M64 BAR can't work on it.
>>
>>The reason is PCI bridges support only 2 windows and the kernel code
>                                        ^^^^^^^^^
>
>It would be more accurate: "2 memory windows".
>

Thanks, will change in next version.

>>programs bridges in the way that one window is 32bit-nonprefetchable and
>>the other one is 64bit-prefetchable. So if devices' IOV BAR is 64bit and
>>non-prefetchable, it will be mapped into 32bit space and therefore M64
>>cannot be used for it.
>>
>>This patch makes this explicit and truncate IOV resource in this case to
>                                    ^^^^^^^^
>>save MMIO space.
>>
>>Signed-off-by: Wei Yang <[email-masked]>
>>Reviewed-by: Gavin Shan <[email-masked]>
>>Acked-by: Alexey Kardashevskiy <[email-masked]>
>>---
>> arch/powerpc/platforms/powernv/pci-ioda.c | 34 ++++++++++++++++---------------
>> 1 file changed, 18 insertions(+), 16 deletions(-)
>>
>>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>>index 85cbc96..f042fed 100644
>>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
>>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>>@@ -908,9 +908,6 @@ static int pnv_pci_vf_resource_shift(struct pci_dev *dev, int offset)
>> 		if (!res->flags || !res->parent)
>> 			continue;
>>
>>-		if (!pnv_pci_is_mem_pref_64(res->flags))
>>-			continue;
>>-
>> 		/*
>> 		 * The actual IOV BAR range is determined by the start address
>> 		 * and the actual size for num_vfs VFs BAR.  This check is to
>>@@ -939,9 +936,6 @@ static int pnv_pci_vf_resource_shift(struct pci_dev *dev, int offset)
>> 		if (!res->flags || !res->parent)
>> 			continue;
>>
>>-		if (!pnv_pci_is_mem_pref_64(res->flags))
>>-			continue;
>>-
>> 		size = pci_iov_resource_size(dev, i + PCI_IOV_RESOURCES);
>> 		res2 = *res;
>> 		res->start += size * offset;
>>@@ -1221,9 +1215,6 @@ static int pnv_pci_vf_assign_m64(struct pci_dev *pdev, u16 num_vfs)
>> 		if (!res->flags || !res->parent)
>> 			continue;
>>
>>-		if (!pnv_pci_is_mem_pref_64(res->flags))
>>-			continue;
>>-
>> 		for (j = 0; j < vf_groups; j++) {
>> 			do {
>> 				win = find_next_zero_bit(&phb->ioda.m64_bar_alloc,
>>@@ -1510,6 +1501,12 @@ int pnv_pci_sriov_enable(struct pci_dev *pdev, u16 num_vfs)
>> 	pdn = pci_get_pdn(pdev);
>>
>> 	if (phb->type == PNV_PHB_IODA2) {
>>+		if (!pdn->vfs_expanded) {
>>+			dev_info(&pdev->dev, "don't support this SRIOV device"
>>+				" with non 64bit-prefetchable IOV BAR\n");
>>+			return -ENOSPC;
>>+		}
>>+
>> 		/* Calculate available PE for required VFs */
>> 		mutex_lock(&phb->ioda.pe_alloc_mutex);
>> 		pdn->offset = bitmap_find_next_zero_area(
>>@@ -2775,9 +2772,10 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
>> 		if (!res->flags || res->parent)
>> 			continue;
>> 		if (!pnv_pci_is_mem_pref_64(res->flags)) {
>>-			dev_warn(&pdev->dev, " non M64 VF BAR%d: %pR\n",
>>+			dev_warn(&pdev->dev, "Don't support SR-IOV with"
>>+					" non M64 VF BAR%d: %pR. \n",
>> 				 i, res);
>>-			continue;
>>+			goto truncate_iov;
>> 		}
>>
>> 		size = pci_iov_resource_size(pdev, i + PCI_IOV_RESOURCES);
>>@@ -2796,11 +2794,6 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
>> 		res = &pdev->resource[i + PCI_IOV_RESOURCES];
>> 		if (!res->flags || res->parent)
>> 			continue;
>>-		if (!pnv_pci_is_mem_pref_64(res->flags)) {
>>-			dev_warn(&pdev->dev, "Skipping expanding VF BAR%d: %pR\n",
>>-				 i, res);
>>-			continue;
>>-		}
>>
>> 		dev_dbg(&pdev->dev, " Fixing VF BAR%d: %pR to\n", i, res);
>> 		size = pci_iov_resource_size(pdev, i + PCI_IOV_RESOURCES);
>>@@ -2810,6 +2803,15 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
>> 			 i, res, mul);
>> 	}
>> 	pdn->vfs_expanded = mul;
>>+
>>+	return;
>>+
>>+truncate_iov:
>>+	/* To save MMIO space, IOV BAR is truncated. */
>>+	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {
>>+		res = &pdev->resource[i + PCI_IOV_RESOURCES];
>>+		res->end = res->start - 1;
>>+	}
>
>res->flags isn't cleared out, the IOV BAR will be counted in the optional list
>in resource sizing stage. However, the size has became zero. It's obvious not
>necessary to do that. I doubt this piece of code has been really testified on
>real PCI adapter or one with emulated M32 IOV BAR?
>

Below is the log during my test:

[    0.436209] pci 0001:08:00.0: reg 0x10: [mem 0x3fe080820000-0x3fe08082ffff 64bit]
[    0.436230] pci 0001:08:00.0: reg 0x18: [mem 0x3fe080830000-0x3fe08083ffff 64bit]
[    0.436268] pci 0001:08:00.0: reg 0x30: [mem 0x00000000-0x0001ffff pref]
[    0.436333] pci 0001:08:00.0: PME# supported from D0 D3hot D3cold
[    0.436402] pci 0001:08:00.0: reg 0x16c: [mem 0x00000000-0x0000ffff 64bit]
[    0.436404] pci 0001:08:00.0: VF(n) BAR0 space: [mem 0x00000000-0x001fffff 64bit] (contains BAR0 for 32 VFs)
[    0.436515] pci 0001:08:00.0: reg 0x174: [mem 0x00000000-0x0000ffff 64bit]
[    0.436517] pci 0001:08:00.0: VF(n) BAR2 space: [mem 0x00000000-0x001fffff 64bit] (contains BAR2 for 32 VFs)

IOV BAR not truncated:

[root@tian-lp1 ~]# grep 0001:08:00.0 /proc/iomem
        3fe080800000-3fe08081ffff : 0001:08:00.0
        3fe080820000-3fe08082ffff : 0001:08:00.0
        3fe080830000-3fe08083ffff : 0001:08:00.0
        3fe080840000-3fe080a3ffff : 0001:08:00.0
        3fe080a40000-3fe080c3ffff : 0001:08:00.0

IOV BAR truncated:

[ywywyang@tian-lp1 ~]$ grep 0001:08:00.0 /proc/iomem 
        3fe080800000-3fe08081ffff : 0001:08:00.0
        3fe080820000-3fe08082ffff : 0001:08:00.0
        3fe080830000-3fe08083ffff : 0001:08:00.0

We could see, after applying this patch, the 2 IOV BAR will not be allocated
in iomem range.

While I think your proposal is reasonable. By clearing the flag, IOV BAR will
not be involved in the sizing/assign stage. Will change this in next version.

>> }
>> #endif /* CONFIG_PCI_IOV */
>>
>>-- 
>>2.5.0
>>

-- 
Richard Yang
Help you, Help me