Date:   Thu, 24 Oct 2019 11:35:01 +0800
From:   Jian-Hong Pan <jian-hong@...lessm.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Matthew Wilcox <willy@...ux.intel.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-nvme@...ts.infradead.org, linux-pci@...r.kernel.org,
        Linux Upstreaming Team <linux@...lessm.com>
Subject: Re: [PATCH] PCI/MSI: Fix restoring of MSI-X vector control's mask bit

Bjorn Helgaas <helgaas@...nel.org> 於 2019年10月24日 週四 上午5:43寫道：
>
> On Wed, Oct 23, 2019 at 04:12:35PM -0500, Bjorn Helgaas wrote:
> > On Tue, Oct 08, 2019 at 11:42:39AM +0800, Jian-Hong Pan wrote:
> > > MSI-X vector control's bit 0 is the mask bit, which masks the
> > > corresponding interrupt request, or not. Other reserved bits might be
> > > used for other purpose by device vendors. For example, the values of
> > > Kingston NVMe SSD's MSI-X vector control are neither 0, nor 1, but other
> > > values [1].
> > >
> > > The original restoring logic in system resuming uses the whole MSI-X
> > > vector control value as the flag to set/clear the mask bit. However,
> > > this logic conflicts the idea mentioned above. It may mislead system to
> > > disable the MSI-X vector entries. That makes system get no interrupt
> > > from Kingston NVMe SSD after resume and usually get NVMe I/O timeout
> > > error.
> > >
> > > [  174.715534] nvme nvme0: I/O 978 QID 3 timeout, completion polled
> > >
> > > This patch takes only the mask bit of original MSI-X vector control
> > > value as the flag to fix this issue.
> > >
> > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=204887#c8
> > >
> > > Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=204887
> > > Fixed: f2440d9acbe8 ("PCI MSI: Refactor interrupt masking code")
> > > Signed-off-by: Jian-Hong Pan <jian-hong@...lessm.com>
> > > ---
> > >  drivers/pci/msi.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> > > index 0884bedcfc7a..deae3d5acaf6 100644
> > > --- a/drivers/pci/msi.c
> > > +++ b/drivers/pci/msi.c
> > > @@ -433,6 +433,7 @@ static void __pci_restore_msi_state(struct pci_dev *dev)
> > >  static void __pci_restore_msix_state(struct pci_dev *dev)
> > >  {
> > >     struct msi_desc *entry;
> > > +   u32 flag;
> > >
> > >     if (!dev->msix_enabled)
> > >             return;
> > > @@ -444,8 +445,10 @@ static void __pci_restore_msix_state(struct pci_dev *dev)
> > >                             PCI_MSIX_FLAGS_ENABLE | PCI_MSIX_FLAGS_MASKALL);
> > >
> > >     arch_restore_msi_irqs(dev);
> > > -   for_each_pci_msi_entry(entry, dev)
> > > -           msix_mask_irq(entry, entry->masked);
> > > +   for_each_pci_msi_entry(entry, dev) {
> > > +           flag = entry->masked & PCI_MSIX_ENTRY_CTRL_MASKBIT;
> > > +           msix_mask_irq(entry, flag);
> >
> > This makes good sense: before your patch, when we restore, we set the
> > mask bit if *any* bits in the Vector Control register are set.
> >
> > There are other paths leading to __pci_msix_desc_mask_irq(), so I
> > think it would be better to do the masking there, e.g.,
> >
> >   if (flag & PCI_MSIX_ENTRY_CTRL_MASKBIT)
> >     mask_bits |= PCI_MSIX_ENTRY_CTRL_MASKBIT;
> >
> > I think the other paths all pass either 0 or 1, so they're all safe
> > today.  But doing the masking in __pci_msix_desc_mask_irq() removes
> > that assumption from the callers.
> >
> > I applied the patch below to pci/msi, let me know if it doesn't work
> > for you.
> >
> > > +   }
> > >
> > >     pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_MASKALL, 0);
> > >  }
> >
> > commit 1a828a554650
> > Author: Jian-Hong Pan <jian-hong@...lessm.com>
> > Date:   Tue Oct 8 11:42:39 2019 +0800
> >
> >     PCI/MSI: Fix incorrect MSI-X masking on resume
> >
> >     When a driver enables MSI-X, msix_program_entries() reads the MSI-X Vector
> >     Control register for each vector and saves it in desc->masked.  Each
> >     register is 32 bits and bit 0 is the actual Mask bit.
> >
> >     When we restored these registers during resume, we previously set the Mask
> >     bit if *any* bit in desc->masked was set instead of when the Mask bit
> >     itself was set:
> >
> >       pci_restore_state
> >         pci_restore_msi_state
> >           __pci_restore_msix_state
> >             for_each_pci_msi_entry
> >               msix_mask_irq(entry, entry->masked)   <-- entire u32 word
> >                 __pci_msix_desc_mask_irq(desc, flag)
> >                   mask_bits = desc->masked & ~PCI_MSIX_ENTRY_CTRL_MASKBIT
> >                   if (flag)       <-- testing entire u32, not just bit 0
> >                     mask_bits |= PCI_MSIX_ENTRY_CTRL_MASKBIT
> >                   writel(mask_bits, desc_addr + PCI_MSIX_ENTRY_VECTOR_CTRL)
> >
> >     This means that after resume, MSI-X vectors were masked when they shouldn't
> >     be, which leads to timeouts like this:
> >
> >       nvme nvme0: I/O 978 QID 3 timeout, completion polled
> >
> >     On resume, set the Mask bit only when the saved Mask bit from suspend was
> >     set.
> >
> >     This should remove the need for 19ea025e1d28 ("nvme: Add quirk for Kingston
> >     NVME SSD running FW E8FK11.T").
> >
> >     [bhelgaas: commit log, move fix to __pci_msix_desc_mask_irq()]
> >     Fixes: f2440d9acbe8 ("PCI MSI: Refactor interrupt masking code")
> >     Link: https://bugzilla.kernel.org/show_bug.cgi?id=204887
> >     Link: https://lore.kernel.org/r/20191008034238.2503-1-jian-hong@endlessm.com
> >     Signed-off-by: Jian-Hong Pan <jian-hong@...lessm.com>
> >     Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>

The modified patch also fixes the issue.

> I forgot; this probably should be marked for stable, too.

Oh!  Yes, please!

Thank you,
Jian-Hong Pan

> > diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> > index 0884bedcfc7a..771041784e64 100644
> > --- a/drivers/pci/msi.c
> > +++ b/drivers/pci/msi.c
> > @@ -213,12 +213,13 @@ u32 __pci_msix_desc_mask_irq(struct msi_desc *desc, u32 flag)
> >
> >       if (pci_msi_ignore_mask)
> >               return 0;
> > +
> >       desc_addr = pci_msix_desc_addr(desc);
> >       if (!desc_addr)
> >               return 0;
> >
> >       mask_bits &= ~PCI_MSIX_ENTRY_CTRL_MASKBIT;
> > -     if (flag)
> > +     if (flag & PCI_MSIX_ENTRY_CTRL_MASKBIT)
> >               mask_bits |= PCI_MSIX_ENTRY_CTRL_MASKBIT;
> >
> >       writel(mask_bits, desc_addr + PCI_MSIX_ENTRY_VECTOR_CTRL);
> >
> > _______________________________________________
> > Linux-nvme mailing list
> > Linux-nvme@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-nvme

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