Subject: Re: [PATCH] powerpc/pseries/eeh: move pseries_eeh_err_inject() outside CONFIG_DEBUG_FS block

From: Ritesh Harjani (IBM) <[email-masked]>
Date: Thu, 19 Sep 2024 21:11:27 +0530

Vaibhav Jain <[email-masked]> writes:

> Hi Ritesh,
>
> Thanks for looking into this patch. My responses your review inline
> below:
>
> Ritesh Harjani (IBM) <[email-masked]> writes:
>
>> Narayana Murty N <[email-masked]> writes:
>>
>>> Makes pseries_eeh_err_inject() available even when debugfs
>>> is disabled (CONFIG_DEBUG_FS=n). It moves eeh_debugfs_break_device()
>>> and eeh_pe_inject_mmio_error() out of the CONFIG_DEBUG_FS block
>>> and renames it as eeh_break_device().
>>>
>>> Reported-by: kernel test robot <[email-masked]>
>>> Closes: https://lore.kernel.org/oe-kbuild-all/[email-masked]/
>>> Fixes: b0e2b828dfca ("powerpc/pseries/eeh: Fix pseries_eeh_err_inject")
>>> Signed-off-by: Narayana Murty N <[email-masked]>
>>> ---
>>>  arch/powerpc/kernel/eeh.c | 198 +++++++++++++++++++-------------------
>>>  1 file changed, 99 insertions(+), 99 deletions(-)
>>
>> Ok, so in your original patch you implemented eeh_inject ops for pseries
>> using mmio based eeh error injection (eeh_pe_inject_mmio_error()), which
>> uses the functions defined under debugfs -> eeh_debugfs_break_device(). 
>>
>> This was failing when CONFIG_DEBUGFS is not defined, thus referring to
>> undefined function definition. 
>>
>> Minor nit below.
>>
>>>
>>> diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
>>> index 49ab11a287a3..0fe25e907ea6 100644
>>> --- a/arch/powerpc/kernel/eeh.c
>>> +++ b/arch/powerpc/kernel/eeh.c
>>> @@ -1574,6 +1574,104 @@ static int proc_eeh_show(struct seq_file *m, void *v)
>>>  }
>>>  #endif /* CONFIG_PROC_FS */
>>>  
>>> +static int eeh_break_device(struct pci_dev *pdev)
>>> +{
>>> +	struct resource *bar = NULL;
>>> +	void __iomem *mapped;
>>> +	u16 old, bit;
>>> +	int i, pos;
>>> +
>>> +	/* Do we have an MMIO BAR to disable? */
>>> +	for (i = 0; i <= PCI_STD_RESOURCE_END; i++) {
>>> +		struct resource *r = &pdev->resource[i];
>>> +
>>> +		if (!r->flags || !r->start)
>>> +			continue;
>>> +		if (r->flags & IORESOURCE_IO)
>>> +			continue;
>>> +		if (r->flags & IORESOURCE_UNSET)
>>> +			continue;
>>> +
>>> +		bar = r;
>>> +		break;
>>> +	}
>>> +
>>> +	if (!bar) {
>>> +		pci_err(pdev, "Unable to find Memory BAR to cause EEH with\n");
>>> +		return -ENXIO;
>>> +	}
>>> +
>>> +	pci_err(pdev, "Going to break: %pR\n", bar);
>>> +
>>> +	if (pdev->is_virtfn) {
>>> +#ifndef CONFIG_PCI_IOV
>>> +		return -ENXIO;
>>> +#else
>>> +		/*
>>> +		 * VFs don't have a per-function COMMAND register, so the best
>>> +		 * we can do is clear the Memory Space Enable bit in the PF's
>>> +		 * SRIOV control reg.
>>> +		 *
>>> +		 * Unfortunately, this requires that we have a PF (i.e doesn't
>>> +		 * work for a passed-through VF) and it has the potential side
>>> +		 * effect of also causing an EEH on every other VF under the
>>> +		 * PF. Oh well.
>>> +		 */
>>> +		pdev = pdev->physfn;
>>> +		if (!pdev)
>>> +			return -ENXIO; /* passed through VFs have no PF */
>>> +
>>> +		pos  = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_SRIOV);
>>> +		pos += PCI_SRIOV_CTRL;
>>> +		bit  = PCI_SRIOV_CTRL_MSE;
>>> +#endif /* !CONFIG_PCI_IOV */
>>> +	} else {
>>> +		bit = PCI_COMMAND_MEMORY;
>>> +		pos = PCI_COMMAND;
>>> +	}
>>> +
>>> +	/*
>>> +	 * Process here is:
>>> +	 *
>>> +	 * 1. Disable Memory space.
>>> +	 *
>>> +	 * 2. Perform an MMIO to the device. This should result in an error
>>> +	 *    (CA  / UR) being raised by the device which results in an EEH
>>> +	 *    PE freeze. Using the in_8() accessor skips the eeh detection hook
>>> +	 *    so the freeze hook so the EEH Detection machinery won't be
>>> +	 *    triggered here. This is to match the usual behaviour of EEH
>>> +	 *    where the HW will asynchronously freeze a PE and it's up to
>>> +	 *    the kernel to notice and deal with it.
>>> +	 *
>>> +	 * 3. Turn Memory space back on. This is more important for VFs
>>> +	 *    since recovery will probably fail if we don't. For normal
>>> +	 *    the COMMAND register is reset as a part of re-initialising
>>> +	 *    the device.
>>> +	 *
>>> +	 * Breaking stuff is the point so who cares if it's racy ;)
>>> +	 */
>>> +	pci_read_config_word(pdev, pos, &old);
>>> +
>>> +	mapped = ioremap(bar->start, PAGE_SIZE);
>>> +	if (!mapped) {
>>> +		pci_err(pdev, "Unable to map MMIO BAR %pR\n", bar);
>>> +		return -ENXIO;
>>> +	}
>>> +
>>> +	pci_write_config_word(pdev, pos, old & ~bit);
>>> +	in_8(mapped);
>>> +	pci_write_config_word(pdev, pos, old);
>>> +
>>> +	iounmap(mapped);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +int eeh_pe_inject_mmio_error(struct pci_dev *pdev)
>>> +{
>>> +	return eeh_break_device(pdev);
>>> +}
>>> +
>>
>> Why have an extra eeh_pe_inject_mmio_error() function which only calls
>> eeh_break_device()?
>>
>> Maybe we can rename eeh_break_device() to eeh_mmio_break_device() and use
>> this function itself at both call sites?
>
> Fair suggestion,
>
> However we want to keep the method debugfs interface uses
> to inject EEH (thats ppc platform agonistic), decoupled from what pseries
> uses. Right now to support as initial work VFIO EEH injection on
> pseries, we are piggy backing on eeh_debugfs_break_device().

Right. 

>
> This will change in future as we add more capabilities to pseries EEH
> injection and this will change working of eeh_pe_inject_mmio_error()
> without impacting the semantics of existing eeh_break_device().

Thanks Vaibhav for the context. 

The debugfs interface "eeh_break_device()" is defined here in
"arch/powerpc/kernel/eeh.c". Those "future pseries changes" could remain
in arch/powerpc/platforms/pseries/eeh_pseries.c using the generic
functions defined from <>/kernel/eeh.c, right. And today
eeh_pe_inject_mmio_error() has nothing pseries specific anyway.

But I get it that this is a minor compile fix for the patch that has
already landed in 6.12 now. As I said earlier too, this was just a minor
nit.

Maybe we could get rid of this redundant function later when we add
pseries specific capabilities (if we still find this extra function has
no use).

So - 

Please feel free to add - 
Reviewed-by: Ritesh Harjani (IBM) <[email-masked]>