Message-ID: <20171219162027.GC21501@red-moon>
Date:   Tue, 19 Dec 2017 16:20:27 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Cao Zou <cao.zou@...driver.com>
Cc:     Marc Zyngier <marc.zyngier@....com>, 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 Mon, Dec 18, 2017 at 10:02:20AM +0800, 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 one warning as Marc said. Mind testing Marc's patch
and reporting the result on the mailing list please if you want
the issue fixed ?

Thanks,
Lorenzo

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