Re: [RFC PATCH kernel 5/5] vfio_pci: Add NVIDIA GV100GL [Tesla V100 SXM2] [10de:1db1] subdriver

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 8 Jun 2018 13:09:13 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> On 8/6/18 3:04 am, Alex Williamson wrote:
> > On Thu,  7 Jun 2018 18:44:20 +1000
> > Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> >> index 7bddf1e..38c9475 100644
> >> --- a/drivers/vfio/pci/vfio_pci.c
> >> +++ b/drivers/vfio/pci/vfio_pci.c
> >> @@ -306,6 +306,15 @@ static int vfio_pci_enable(struct vfio_pci_device *vdev)
> >>  		}
> >>  	}
> >>  
> >> +	if (pdev->vendor == PCI_VENDOR_ID_NVIDIA &&
> >> +	    pdev->device == 0x1db1 &&
> >> +	    IS_ENABLED(CONFIG_VFIO_PCI_NVLINK2)) {  
> > 
> > Can't we do better than check this based on device ID?  Perhaps PCIe
> > capability hints at this?  
> 
> A normal PCI pluggable device looks like this:
> 
> root@fstn3:~# sudo lspci -vs 0000:03:00.0
> 0000:03:00.0 3D controller: NVIDIA Corporation GK210GL [Tesla K80] (rev a1)
> 	Subsystem: NVIDIA Corporation GK210GL [Tesla K80]
> 	Flags: fast devsel, IRQ 497
> 	Memory at 3fe000000000 (32-bit, non-prefetchable) [disabled] [size=16M]
> 	Memory at 200000000000 (64-bit, prefetchable) [disabled] [size=16G]
> 	Memory at 200400000000 (64-bit, prefetchable) [disabled] [size=32M]
> 	Capabilities: [60] Power Management version 3
> 	Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
> 	Capabilities: [78] Express Endpoint, MSI 00
> 	Capabilities: [100] Virtual Channel
> 	Capabilities: [128] Power Budgeting <?>
> 	Capabilities: [420] Advanced Error Reporting
> 	Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 <?>
> 	Capabilities: [900] #19
> 
> 
> This is a NVLink v1 machine:
> 
> aik@garrison1:~$ sudo lspci -vs 000a:01:00.0
> 000a:01:00.0 3D controller: NVIDIA Corporation Device 15fe (rev a1)
> 	Subsystem: NVIDIA Corporation Device 116b
> 	Flags: bus master, fast devsel, latency 0, IRQ 457
> 	Memory at 3fe300000000 (32-bit, non-prefetchable) [size=16M]
> 	Memory at 260000000000 (64-bit, prefetchable) [size=16G]
> 	Memory at 260400000000 (64-bit, prefetchable) [size=32M]
> 	Capabilities: [60] Power Management version 3
> 	Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
> 	Capabilities: [78] Express Endpoint, MSI 00
> 	Capabilities: [100] Virtual Channel
> 	Capabilities: [250] Latency Tolerance Reporting
> 	Capabilities: [258] L1 PM Substates
> 	Capabilities: [128] Power Budgeting <?>
> 	Capabilities: [420] Advanced Error Reporting
> 	Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 <?>
> 	Capabilities: [900] #19
> 	Kernel driver in use: nvidia
> 	Kernel modules: nvidiafb, nouveau, nvidia_384_drm, nvidia_384
> 
> 
> This is the one the patch is for:
> 
> [aik@yc02goos ~]$ sudo lspci -vs 0035:03:00.0
> 0035:03:00.0 3D controller: NVIDIA Corporation GV100GL [Tesla V100 SXM2]
> (rev a1)
> 	Subsystem: NVIDIA Corporation Device 1212
> 	Flags: fast devsel, IRQ 82, NUMA node 8
> 	Memory at 620c280000000 (32-bit, non-prefetchable) [disabled] [size=16M]
> 	Memory at 6228000000000 (64-bit, prefetchable) [disabled] [size=16G]
> 	Memory at 6228400000000 (64-bit, prefetchable) [disabled] [size=32M]
> 	Capabilities: [60] Power Management version 3
> 	Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
> 	Capabilities: [78] Express Endpoint, MSI 00
> 	Capabilities: [100] Virtual Channel
> 	Capabilities: [250] Latency Tolerance Reporting
> 	Capabilities: [258] L1 PM Substates
> 	Capabilities: [128] Power Budgeting <?>
> 	Capabilities: [420] Advanced Error Reporting
> 	Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 <?>
> 	Capabilities: [900] #19
> 	Capabilities: [ac0] #23
> 	Kernel driver in use: vfio-pci
> 
> 
> I can only see a new capability #23 which I have no idea about what it
> actually does - my latest PCIe spec is
> PCI_Express_Base_r3.1a_December7-2015.pdf and that only knows capabilities
> till #21, do you have any better spec? Does not seem promising anyway...

You could just look in include/uapi/linux/pci_regs.h and see that 23
(0x17) is a TPH Requester capability and google for that...  It's a TLP
processing hint related to cache processing for requests from system
specific interconnects.  Sounds rather promising.  Of course there's
also the vendor specific capability that might be probed if NVIDIA will
tell you what to look for and the init function you've implemented
looks for specific devicetree nodes, that I imagine you could test for
in a probe as well.

> > Is it worthwhile to continue with assigning the device in the !ENABLED
> > case?  For instance, maybe it would be better to provide a weak
> > definition of vfio_pci_nvlink2_init() that would cause us to fail here
> > if we don't have this device specific support enabled.  I realize
> > you're following the example set forth for IGD, but those regions are
> > optional, for better or worse.  
> 
> 
> The device is supposed to work even without GPU RAM passed through, this
> should look like NVLink v1 in this case (there used to be bugs in the
> driver, may be still are, have not checked for a while but there is a bug
> opened at NVIDIA about this and they were going to fix that), this is why I
> chose not to fail here.

Ok.

> >> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> >> index 24ee260..2725bc8 100644
> >> --- a/drivers/vfio/pci/Kconfig
> >> +++ b/drivers/vfio/pci/Kconfig
> >> @@ -30,3 +30,7 @@ config VFIO_PCI_INTX
> >>  config VFIO_PCI_IGD
> >>  	depends on VFIO_PCI
> >>  	def_bool y if X86
> >> +
> >> +config VFIO_PCI_NVLINK2
> >> +	depends on VFIO_PCI
> >> +	def_bool y if PPC_POWERNV  
> > 
> > As written, this also depends on PPC_POWERNV (or at least TCE), it's not
> > a portable implementation that we could re-use on X86 or ARM or any
> > other platform if hardware appeared for it.  Can we improve that as
> > well to make this less POWER specific?  Thanks,  
> 
> 
> As I said in another mail, every P9 chip in that box has some NVLink2 logic
> on it so it is not even common among P9's in general and I am having hard
> time seeing these V100s used elsewhere in such way.

https://www.redhat.com/archives/vfio-users/2018-May/msg00000.html

Not much platform info, but based on the rpm mentioned, looks like an
x86_64 box.  Thanks,

Alex