Date:   Mon, 18 Dec 2017 09:32:47 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Cao Zou <cao.zou@...driver.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     jingoohan1@...il.com, Joao.Pinto@...opsys.com, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: designware: add a check of msi_desc in irqchip

On 18/12/17 02:02, Cao Zou wrote:
> 
> 
> On 12/16/2017 01:20 AM, Marc Zyngier wrote:
>> On 15/12/17 16:17, Lorenzo Pieralisi wrote:
>>> [+Marc]
>>>
>>> On Thu, Dec 14, 2017 at 10:21:23AM +0800, cao.zou@...driver.com wrote:
>>>> From: Zou Cao <cao.zou@...driver.com>
>>>>
>>>> When PCIE host setup, 32 MSI irq descriptions are created, but its
>>>> msi_desc is NULL, msi_desc is bound in MSI irq requested by PCI device,
>>>> normally just part of MSI are used, for others not used MSI irqs, its
>>>> msi_desc is NULL, it is dangerous for MSI irq mask when MSI irq mask use
>>>> the msi_desc to mask irq without checking, normally not used MSI irqs are
>>>> never masked, it looks fine, but in some specified case, such as kdump,
>>>> machine_kexec_mask_interrupts will force to mask these not used MSI irqs,
>>>> than a crash will happen with NULL msi_desc. it is necessary to add check
>>>> of msi_desc in irqchip, if we still bind the msi_desc only in irqs request
>>>> and mask MSI irq by msi_desc.
>>>>
>>>> Add dwc_pci_msi_mask/unmask_irq, so we can get a chance to check the
>>>> msi_desc.
>>>>
>>>> here is reproduced crash log in IMX7-SABER board with Intel 1030 PCI,
>>>> when running kdump by "echo c > /proc/sysrq-trigger":
>>>>
>>>> sysrq: SysRq : Trigger a crash
>>>> Unable to handle kernel NULL pointer dereference at virtual address 00000000
>>>> pgd = 98ee1839
>>>> [00000000] *pgd=00000000
>>>> Internal error: Oops: 805 [#1] SMP ARM
>>>> Modules linked in:
>>>> CPU: 0 PID: 1370 Comm: sh Not tainted 4.15.0-rc3-00033-ga638349 #1
>>>> Hardware name: Freescale i.MX7 Dual (Device Tree)
>>>> PC is at sysrq_handle_crash+0x50/0x98
>>>> LR is at sysrq_handle_crash+0x50/0x98
>>>> <snip>
>>>> Backtrace:
>>>> [<c047a15c>] (msi_set_mask_bit) from [<c047a1f0>] (pci_msi_mask_irq+0x14/0x18)
>>>> [<c047a1dc>] (pci_msi_mask_irq) from [<c011142c>] (machine_crash_shutdown+0xd8/0x190)
>>>> [<c0111354>] (machine_crash_shutdown) from [<c01b2924>] (__crash_kexec+0x5c/0xa0)
>>>> [<c01b28c8>] (__crash_kexec) from [<c01b29dc>] (crash_kexec+0x74/0x80)
>>>> [<c01b2968>] (crash_kexec) from [<c010cfa4>] (die+0x220/0x358)
>>>> [<c010cd84>] (die) from [<c01169f0>] (__do_kernel_fault.part.0+0x5c/0x7c)
>>>> [<c0116994>] (__do_kernel_fault.part.0) from [<c0116784>] (do_page_fault+0x2cc/0x37c)
>>>> [<c01164b8>] (do_page_fault) from [<c0116970>] (do_translation_fault+0xb0/0xbc)
>>>> [<c01168c0>] (do_translation_fault) from [<c010138c>] (do_DataAbort+0x3c/0xbc)
>>>> [<c0101350>] (do_DataAbort) from [<c010d944>] (__dabt_svc+0x64/0xa0)
>>>> Exception stack(0xec08bdf8 to 0xec08be40)
>>>> bde0:                                                       00000000 ec08be10
>>>> be00: 00000000 00000000 00000000 00000001 00000063 00000000 00000007 ec08a000
>>>> be20: 00000000 ec08be5c ec08be48 ec08be48 c04c46b8 c04c46b8 60060013 ffffffff
>>>> [<c04c4668>] (sysrq_handle_crash) from [<c04c4900>] (__handle_sysrq+0xe0/0x254)
>>>> [<c04c4820>] (__handle_sysrq) from [<c04c4aec>] (write_sysrq_trigger+0x78/0x90)
>>>> [<c04c4a74>] (write_sysrq_trigger) from [<c029148c>] (proc_reg_write+0x68/0x90)
>>>> [<c0291424>] (proc_reg_write) from [<c0229ef8>] (__vfs_write+0x34/0x12c)
>>>> [<c0229ec4>] (__vfs_write) from [<c022a16c>] (vfs_write+0xa8/0x16c)
>>>> [<c022a0c4>] (vfs_write) from [<c022a340>] (SyS_write+0x44/0x90)
>>>> [<c022a2fc>] (SyS_write) from [<c0108220>] (ret_fast_syscall+0x0/0x28)
>>>>
>>>> Signed-off-by: Zou Cao <cao.zou@...driver.com>
>>>> ---
>>>>   drivers/pci/dwc/pcie-designware-host.c | 24 ++++++++++++++++++++----
>>>>   1 file changed, 20 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/dwc/pcie-designware-host.c b/drivers/pci/dwc/pcie-designware-host.c
>>>> index 81e2157..485c4df 100644
>>>> --- a/drivers/pci/dwc/pcie-designware-host.c
>>>> +++ b/drivers/pci/dwc/pcie-designware-host.c
>>>> @@ -45,12 +45,28 @@ static int dw_pcie_wr_own_conf(struct pcie_port *pp, int where, int size,
>>>>   	return dw_pcie_write(pci->dbi_base + where, size, val);
>>>>   }
>>>>   
>>>> +static void dwc_pci_msi_mask_irq(struct irq_data *data)
>>>> +{
>>>> +	struct msi_desc *desc = irq_data_get_msi_desc(data);
>>>> +
>>>> +	if (desc)
>>>> +		pci_msi_mask_irq(data);
>>>> +}
>>>> +
>>>> +static void dwc_pci_msi_unmask_irq(struct irq_data *data)
>>>> +{
>>>> +	struct msi_desc *desc = irq_data_get_msi_desc(data);
>>>> +
>>>> +	if (desc)
>>>> +		pci_msi_unmask_irq(data);
>>>> +}
>>>> +
>>>>   static struct irq_chip dw_msi_irq_chip = {
>>>>   	.name = "PCI-MSI",
>>>> -	.irq_enable = pci_msi_unmask_irq,
>>>> -	.irq_disable = pci_msi_mask_irq,
>>>> -	.irq_mask = pci_msi_mask_irq,
>>>> -	.irq_unmask = pci_msi_unmask_irq,
>>>> +	.irq_enable = dwc_pci_msi_unmask_irq,
>>>> +	.irq_disable = dwc_pci_msi_mask_irq,
>>>> +	.irq_mask = dwc_pci_msi_mask_irq,
>>>> +	.irq_unmask = dwc_pci_msi_unmask_irq,
>>>>   };
>>> You have to CC me next time please.
>>>
>>> CC'ed Marc since he knows this code ways better than me and will
>>> help us find the right way of fixing it.
>>>
>>> I do not think that's a DWC-only problem - I see no reason why this
>>> would not affect other host bridges still relying on
>>> struct msi_controller (that we have to remove from the kernel).
>>>
>>> I do not think that this code is an actual fix but a plaster to
>>> paper over the issue - I will have a look into this as soon as
>>> possible to come up with an actual fix.
>> Yeah, this looks mad. The problem is that this seems to allocate
>> interrupts upfront, without being bound to an MSI. What could possibly
>> go wrong? And that's definitely not the only one (pci-tegra.c is one
>> fine example too).
>>
>> Until we take msi_controller and co to the backyard, how about the
>> following:
>>
>> >From b4aa5d20ee7b716795ac875e180f564fe0f52de6 Mon Sep 17 00:00:00 2001
>> From: Marc Zyngier <marc.zyngier@....com>
>> Date: Fri, 15 Dec 2017 17:10:14 +0000
>> Subject: [PATCH] PCI/MSI: Don't try to mask/unmask an MSI that doesn't have an
>>   msi_desc
>>
>> There are a lot of MSI drivers out there that preallocate their
>> interrupts but not the corresponding MSIs. That's a prettty
>> naughty behaviour. On a kexec crash, we try to shut down all
>> the interrupts by calling the disable/mask methods.
>>
>> On these drivers, pci_msi_mask_irq() is unconditionnaly called,
>> leading to a crash. You wanted a crash kernel, right?
>>
>> So let's paper over the issue for the time being by detecting
>> the NULL msi_desc in msi_set_mask_bit(). Eventually, these drivers
>> will have to be fixed...
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
>> ---
>>   drivers/pci/msi.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>> index e06607167858..a5042cc8f3fc 100644
>> --- a/drivers/pci/msi.c
>> +++ b/drivers/pci/msi.c
>> @@ -227,6 +227,9 @@ static void msi_set_mask_bit(struct irq_data *data, u32 flag)
>>   {
>>   	struct msi_desc *desc = irq_data_get_msi_desc(data);
>>   
>> +	if (WARN_ONCE(!desc, "NULL MSI descriptor!"))
>> +		return;
>> +
>>   	if (desc->msi_attrib.is_msix) {
>>   		msix_mask_irq(desc, flag);
>>   		readl(desc->mask_base);		/* Flush write to device */
> For "if (WARN_ONCE(!desc, "NULL MSI descriptor!")",  it is a good way,
> just one problem. how to fix the kexec/kdump?  this WARN_ONCE can tell
> the pci dirver to fix the MIS bound problem, but in kexec/kdump, it will 
> force
> to mask all MSI,  it means that there are a lot of WARNINGS when running 
> kexec/kdump.

There will be exactly *one* warning. That's what the _ONCE suffix
indicates. What makes you think that this doesn't solve your issue with
kexec? If this doesn't work for you, please let me know why.

In general, warnings are a good thing. They remind you that the software
you're using is broken and needs fixing.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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