RE: [PATCH] PCI: Make SR-IOV capable GPU working on the SR-IOV incapable platform

From: Zytaruk, Kelly
Date: Sat May 20 2017 - 06:28:12 EST

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>-----Original Message-----
>From: Cheng, Collins
>Sent: Saturday, May 20, 2017 12:53 AM
>To: Alexander Duyck; Alex Williamson
>Cc: Bjorn Helgaas; linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>Deucher, Alexander; Zytaruk, Kelly; Yinghai Lu
>Subject: RE: [PATCH] PCI: Make SR-IOV capable GPU working on the SR-IOV
>incapable platform
>
>Hi Alex,
>
>Yes, I hope kernel can disable SR-IOV and related VF resource allocation if the
>system BIOS is not SR-IOV capable.
>
>Adding the parameter "pci=nosriov" sounds a doable solution, but it would need
>user to add this parameter manually, right? I think an automatic detection would
>be better. My patch is trying to auto detect and bypass VF resource allocation.
>
>
>-Collins Cheng
>

Collins, be careful about this. I don't think that this is what we want. If you add "pci=nosriov" then you are globally disabling SRIOV for all devices. This is not the solution that we are looking for.
Remember that there are 3 types of SBIOS;
"not SR-IOV capable",
"SR-IOV capable but does not support large resources",
"Complete SR-IOV support".

The problem is that we are trying to find a fix for "broken" SBIOS that does support SR-IOV but does not support the full SR-IOV capabilities that devices with large resources require.

Thanks,
Kelly

>
>-----Original Message-----
>From: Alexander Duyck [mailto:alexander.duyck@xxxxxxxxx]
>Sent: Friday, May 19, 2017 11:44 PM
>To: Alex Williamson <alex.williamson@xxxxxxxxxx>
>Cc: Cheng, Collins <Collins.Cheng@xxxxxxx>; Bjorn Helgaas
><bhelgaas@xxxxxxxxxx>; linux-pci@xxxxxxxxxxxxxxx; linux-
>kernel@xxxxxxxxxxxxxxx; Deucher, Alexander <Alexander.Deucher@xxxxxxx>;
>Zytaruk, Kelly <Kelly.Zytaruk@xxxxxxx>; Yinghai Lu <yinghai@xxxxxxxxxx>
>Subject: Re: [PATCH] PCI: Make SR-IOV capable GPU working on the SR-IOV
>incapable platform
>
>On Mon, May 15, 2017 at 10:53 AM, Alex Williamson
><alex.williamson@xxxxxxxxxx> wrote:
>> On Mon, 15 May 2017 08:19:28 +0000
>> "Cheng, Collins" <Collins.Cheng@xxxxxxx> wrote:
>>
>>> Hi Williamson,
>>>
>>> We cannot assume BIOS supports SR-IOV, actually only newer server
>motherboard BIOS supports SR-IOV. Normal desktop motherboard BIOS or older
>server motherboard BIOS doesn't support SR-IOV. This issue would happen if an
>user plugs our AMD SR-IOV capable GPU card to a normal desktop motherboard.
>>
>> Servers should be supporting SR-IOV for a long time now. What really
>> is there to a BIOS supporting SR-IOV anyway, it's simply reserving
>> sufficient bus number and MMIO resources such that we can enable the
>> VFs. This process isn't exclusively reserved for the BIOS. Some
>> platforms may choose to only initialize boot devices, leaving the rest
>> for the OS to program. The initial proposal here to disable SR-IOV if
>> not programmed at OS hand-off disables even the possibility of the OS
>> reallocating resources for this device.
>
>There are differences between supporting SR-IOV and supporting SR-IOV on
>devices with massive resources. I know I have seen NICs that will keep a system
>from completing POST if SR-IOV is enabled, and MMIO beyond 4G is not. My
>guess would be that the issues being seen are probably that they disable SR-IOV in
>the BIOS in such a setup and end up running into issues when they try to boot into
>the Linux kernel as it goes through and tries to allocate resources for SR-IOV even
>though it was disabled in the BIOS.
>
>It might make sense to add a kernel parameter something like a "pci=nosriov"
>that would allow for disabling SR-IOV and related resource allocation if that is
>what we are talking about. That way you could plug in these types of devices into
>a system with a legacy bios or that doesn't wan to allocate addresses above 32b
>for MMIO, and this parameter would be all that is needed to disable SR-IOV so
>you could plug in a NIC that has SR-IOV associated with it.
>
>>> I agree that failure to allocate VF resources should leave the device in no
>worse condition than before it tried. I hope kernel could allocate PF device
>resource before allocating VF device resource, and keep PF device resource valid
>and functional if failed to allocate VF device resource.
>>>
>>> I will send out dmesg log lspci info tomorrow. Thanks.
>>
>> Thanks,
>> Alex
>>
>>> -----Original Message-----
>>> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
>>> Sent: Friday, May 12, 2017 10:43 PM
>>> To: Cheng, Collins <Collins.Cheng@xxxxxxx>
>>> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; linux-pci@xxxxxxxxxxxxxxx;
>>> linux-kernel@xxxxxxxxxxxxxxx; Deucher, Alexander
>>> <Alexander.Deucher@xxxxxxx>; Zytaruk, Kelly <Kelly.Zytaruk@xxxxxxx>;
>>> Yinghai Lu <yinghai@xxxxxxxxxx>
>>> Subject: Re: [PATCH] PCI: Make SR-IOV capable GPU working on the
>>> SR-IOV incapable platform
>>>
>>> On Fri, 12 May 2017 04:51:43 +0000
>>> "Cheng, Collins" <Collins.Cheng@xxxxxxx> wrote:
>>>
>>> > Hi Williamson,
>>> >
>>> > I verified the patch is working for both AMD SR-IOV GPU and Intel SR-IOV
>NIC. I don't think it is redundant to check the VF BAR valid before call sriov_init(),
>it is safe and saving boot time, also there is no a better method to know if system
>BIOS has correctly initialized the SR-IOV capability or not.
>>>
>>> It also masks an underlying bug and creates a maintenance issue that we won't
>know when it's safe to remove this workaround. I don't think faster boot is valid
>rationale, in one case SR-IOV is completely disabled, the other we attempt to
>allocate the resources the BIOS failed to provide. I expect this is also a corner
>case, the BIOS should typically support SR-IOV, therefore this situation should be
>an exception.
>>>
>>> > I did not try to fix the issue from the kernel resource allocation perspective,
>it is because:
>>> > 1. I am not very familiar with the PCI resource allocation scheme in kernel.
>For example, in sriov_init(), kernel will re-assign the PCI resource for both VF and
>PF. I don't understand why kernel allocates resource for VF firstly, then PF. If it is
>PF firstly, then this issue could be avoided.
>>> > 2. I am not sure if kernel has error handler if PCI resource allocation failed.
>In this case, kernel cannot allocate enough resource to PF. It should trigger some
>error handler to either just keep original BAR values set by system BIOS, or disable
>this device and log errors.
>>>
>>> I think these are the issues we should be trying to solve and I'm
>>> sure folks on the linux-pci list can help us identify the bug.
>>> Minimally, failure to allocate VF resources should leave the device
>>> in no worse condition than before it tried. Perhaps you could post
>>> more details about the issue, boot with pci=earlydump, post dmesg of
>>> a boot where the PF resources are incorrectly re-allocated, and
>>> include lspci -vvv for the SR-IOV device. Also, please test with the
>>> latest upstream kernel, upstream only patches old kernels through
>>> stable backports of commits to the latest kernel. Adding Yinghai as
>>> a resource allocation expert. Thanks,
>>>
>>> Alex
>>>
>>> > -----Original Message-----
>>> > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
>>> > Sent: Friday, May 12, 2017 12:01 PM
>>> > To: Cheng, Collins <Collins.Cheng@xxxxxxx>
>>> > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; linux-pci@xxxxxxxxxxxxxxx;
>>> > linux-kernel@xxxxxxxxxxxxxxx; Deucher, Alexander
>>> > <Alexander.Deucher@xxxxxxx>; Zytaruk, Kelly <Kelly.Zytaruk@xxxxxxx>
>>> > Subject: Re: [PATCH] PCI: Make SR-IOV capable GPU working on the
>>> > SR-IOV incapable platform
>>> >
>>> > On Fri, 12 May 2017 03:42:46 +0000
>>> > "Cheng, Collins" <Collins.Cheng@xxxxxxx> wrote:
>>> >
>>> > > Hi Williamson,
>>> > >
>>> > > GPU card needs more BAR aperture resource than other PCI devices. For
>example, Intel SR-IOV network card only require 512KB memory resource for all
>VFs. AMD SR-IOV GPU card needs 256MB x16 VF = 4GB memory resource for
>frame buffer BAR aperture.
>>> > >
>>> > > If the system BIOS supports SR-IOV, it will reserve enough resource for all
>VF BARs. If the system BIOS doesn't support SR-IOV or cannot allocate the
>enough resource for VF BARs, only PF BAR will be assigned and VF BARs are
>empty. Then system boots to Linux kernel and kernel doesn't check if the VF BARs
>are empty or valid. Kernel will re-assign the BAR resources for PF and all VFs. The
>problem I saw is that kernel will fail to allocate PF BAR resource because some
>resources are assigned to VF, this is not expected. So kernel might need to do
>some check before re-assign the PF/VF resource, so that PF device will be
>correctly assigned BAR resource and user can use PF device.
>>> >
>>> > So the problem is that something bad happens when the kernel is
>>> > trying to reallocate resources in order to fulfill the requirements
>>> > of the VFs, leaving the PF resources incorrectly programmed? Why
>>> > not just fix that bug rather than creating special handling for
>>> > this vendor/class of device which disables any attempt to fixup
>>> > resources for SR-IOV? IOW, this patch just avoids the problem for
>>> > your devices rather than fixing the bug. I'd suggest fixing the
>>> > bug such that the PF is left in a functional state if the kernel is
>>> > unable to allocate sufficient resources for the VFs. Thanks,
>>> >
>>> > Alex
>>> >
>>> > > -----Original Message-----
>>> > > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
>>> > > Sent: Friday, May 12, 2017 11:21 AM
>>> > > To: Cheng, Collins <Collins.Cheng@xxxxxxx>
>>> > > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>;
>>> > > linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Deucher,
>>> > > Alexander <Alexander.Deucher@xxxxxxx>; Zytaruk, Kelly
>>> > > <Kelly.Zytaruk@xxxxxxx>
>>> > > Subject: Re: [PATCH] PCI: Make SR-IOV capable GPU working on the
>>> > > SR-IOV incapable platform
>>> > >
>>> > > On Fri, 12 May 2017 02:50:32 +0000 "Cheng, Collins"
>>> > > <Collins.Cheng@xxxxxxx> wrote:
>>> > >
>>> > > > Hi Helgaas,
>>> > > >
>>> > > > Some AMD GPUs have hardware support for graphics SR-IOV.
>>> > > > If the SR-IOV capable GPU is plugged into the SR-IOV incapable
>>> > > > platform. It would cause a problem on PCI resource allocation
>>> > > > in current Linux kernel.
>>> > > >
>>> > > > Therefore in order to allow the PF (Physical Function) device
>>> > > > of SR-IOV capable GPU to work on the SR-IOV incapable platform,
>>> > > > it is required to verify conditions for initializing BAR
>>> > > > resources on AMD SR-IOV capable GPUs.
>>> > > >
>>> > > > If the device is an AMD graphics device and it supports SR-IOV
>>> > > > it will require a large amount of resources.
>>> > > > Before calling sriov_init() must ensure that the system BIOS
>>> > > > also supports SR-IOV and that system BIOS has been able to
>>> > > > allocate enough resources.
>>> > > > If the VF BARs are zero then the system BIOS does not support
>>> > > > SR-IOV or it could not allocate the resources and this platform
>>> > > > will not support AMD graphics SR-IOV.
>>> > > > Therefore do not call sriov_init().
>>> > > > If the system BIOS does support SR-IOV then the VF BARs will be
>>> > > > properly initialized to non-zero values.
>>> > > >
>>> > > > Below is the patch against to Kernel 4.8 & 4.9. Please review.
>>> > > >
>>> > > > I checked the drivers/pci/quirks.c, it looks the
>>> > > > workarounds/fixes in quirks.c are for specific devices and one
>>> > > > or more device ID are defined for the specific devices. However
>>> > > > my patch is for all AMD SR-IOV capable GPUs, that includes all existing
>and future AMD server GPUs.
>>> > > > So it doesn't seem like a good fit to put the fix in quirks.c.
>>> > >
>>> > >
>>> > > Why is an AMD graphics card unique here? Doesn't sriov_init()
>>> > > always need to be able to deal with devices of any type where the
>>> > > BIOS hasn't initialized the SR-IOV capability? Some SR-IOV
>>> > > devices can fit their VFs within a minimum bridge aperture, most
>>> > > cannot. I don't understand why the VF resource requirements
>>> > > being exceptionally large dictates that they receive special handling.
>>> > > Thanks,
>>> > >
>>> > > Alex
>>> > >
>>> > > > Signed-off-by: Collins Cheng <collins.cheng@xxxxxxx>
>>> > > > ---
>>> > > > drivers/pci/iov.c | 63
>>> > > > ++++++++++++++++++++++++++++++++++++++++++++++++++++---
>>> > > > 1 file changed, 60 insertions(+), 3 deletions(-)
>>> > > >
>>> > > > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c index
>>> > > > e30f05c..e4f1405 100644
>>> > > > --- a/drivers/pci/iov.c
>>> > > > +++ b/drivers/pci/iov.c
>>> > > > @@ -523,6 +523,45 @@ static void sriov_restore_state(struct pci_dev
>*dev)
>>> > > > msleep(100);
>>> > > > }
>>> > > >
>>> > > > +/*
>>> > > > + * pci_vf_bar_valid - check if VF BARs have resource allocated
>>> > > > + * @dev: the PCI device
>>> > > > + * @pos: register offset of SR-IOV capability in PCI config
>>> > > > +space
>>> > > > + * Returns true any VF BAR has resource allocated, false
>>> > > > + * if all VF BARs are empty.
>>> > > > + */
>>> > > > +static bool pci_vf_bar_valid(struct pci_dev *dev, int pos) {
>>> > > > + int i;
>>> > > > + u32 bar_value;
>>> > > > + u32 bar_size_mask = ~(PCI_BASE_ADDRESS_SPACE |
>>> > > > + PCI_BASE_ADDRESS_MEM_TYPE_64 |
>>> > > > + PCI_BASE_ADDRESS_MEM_PREFETCH);
>>> > > > +
>>> > > > + for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {
>>> > > > + pci_read_config_dword(dev, pos + PCI_SRIOV_BAR + i * 4,
>&bar_value);
>>> > > > + if (bar_value & bar_size_mask)
>>> > > > + return true;
>>> > > > + }
>>> > > > +
>>> > > > + return false;
>>> > > > +}
>>> > > > +
>>> > > > +/*
>>> > > > + * is_amd_display_adapter - check if it is an AMD/ATI GPU
>>> > > > +device
>>> > > > + * @dev: the PCI device
>>> > > > + *
>>> > > > + * Returns true if device is an AMD/ATI display adapter,
>>> > > > + * otherwise return false.
>>> > > > + */
>>> > > > +
>>> > > > +static bool is_amd_display_adapter(struct pci_dev *dev) {
>>> > > > + return (((dev->class >> 16) == PCI_BASE_CLASS_DISPLAY) &&
>>> > > > + (dev->vendor == PCI_VENDOR_ID_ATI ||
>>> > > > + dev->vendor == PCI_VENDOR_ID_AMD)); }
>>> > > > +
>>> > > > /**
>>> > > > * pci_iov_init - initialize the IOV capability
>>> > > > * @dev: the PCI device
>>> > > > @@ -537,9 +576,27 @@ int pci_iov_init(struct pci_dev *dev)
>>> > > > return -ENODEV;
>>> > > >
>>> > > > pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_SRIOV);
>>> > > > - if (pos)
>>> > > > - return sriov_init(dev, pos);
>>> > > > -
>>> > > > + if (pos) {
>>> > > > + /*
>>> > > > + * If the device is an AMD graphics device and it supports
>>> > > > + * SR-IOV it will require a large amount of resources.
>>> > > > + * Before calling sriov_init() must ensure that the system
>>> > > > + * BIOS also supports SR-IOV and that system BIOS has been
>>> > > > + * able to allocate enough resources.
>>> > > > + * If the VF BARs are zero then the system BIOS does not
>>> > > > + * support SR-IOV or it could not allocate the resources
>>> > > > + * and this platform will not support AMD graphics SR-IOV.
>>> > > > + * Therefore do not call sriov_init().
>>> > > > + * If the system BIOS does support SR-IOV then the VF BARs
>>> > > > + * will be properly initialized to non-zero values.
>>> > > > + */
>>> > > > + if (is_amd_display_adapter(dev)) {
>>> > > > + if (pci_vf_bar_valid(dev, pos))
>>> > > > + return sriov_init(dev, pos);
>>> > > > + } else {
>>> > > > + return sriov_init(dev, pos);
>>> > > > + }
>>> > > > + }
>>> > > > return -ENODEV;
>>> > > > }
>>> > > >
>>> > >
>>> >
>>>
>>

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