Re: [Intel-wired-lan] [PATCH] PCI: Check/Set ARI capability before setting numVFs

[Bjorn Helgaas]

On Wed, Oct 04, 2017 at 04:29:14PM -0700, Alexander Duyck wrote:
> On Wed, Oct 4, 2017 at 4:01 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > On Wed, Oct 04, 2017 at 08:52:58AM -0700, Tony Nguyen wrote:
> >> This fixes a bug that can occur if an AER error is encountered while SRIOV
> >> devices are present.
> >>
> >> This issue was seen by doing the following. Inject an AER error to a device
> >> that has SRIOV devices.  After the device has recovered, remove the driver.
> >> Reload the driver and enable SRIOV which causes the following crash to
> >> occur:
> >>
> >> kernel BUG at drivers/pci/iov.c:157!
> >> invalid opcode: 0000 [#1] SMP
> >> CPU: 36 PID: 2295 Comm: bash Not tainted 4.14.0-rc1+ #74
> >> Hardware name: Supermicro X9DAi/X9DAi, BIOS 3.0a 04/29/2014
> >> task: ffff9fa41cd45a00 task.stack: ffffb4b2036e8000
> >> RIP: 0010:pci_iov_add_virtfn+0x2eb/0x350
> >> RSP: 0018:ffffb4b2036ebcb8 EFLAGS: 00010286
> >> RAX: 00000000fffffff0 RBX: ffff9fa42c1c8800 RCX: ffff9fa421ce2388
> >> RDX: 00000000df900000 RSI: ffff9fa8214fb388 RDI: 00000000df903fff
> >> RBP: ffffb4b2036ebd18 R08: ffff9fa421ce23b8 R09: ffffb4b2036ebc2c
> >> R10: ffff9fa42c1a5548 R11: 000000000000058e R12: ffff9fa8214fb000
> >> R13: ffff9fa42c1a5000 R14: ffff9fa8214fb388 R15: 0000000000000000
> >> FS:  00007f60724b6700(0000) GS:ffff9fa82f300000(0000)
> >> knlGS:0000000000000000
> >> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> CR2: 0000559eca8b0f40 CR3: 0000000864146000 CR4: 00000000001606e0
> >> Call Trace:
> >>  pci_enable_sriov+0x353/0x440
> >>  ixgbe_pci_sriov_configure+0xd5/0x1f0 [ixgbe]
> >>  sriov_numvfs_store+0xf7/0x170
> >>  dev_attr_store+0x18/0x30
> >>  sysfs_kf_write+0x37/0x40
> >>  kernfs_fop_write+0x120/0x1b0
> >>  __vfs_write+0x37/0x170
> >>  ? __alloc_fd+0x3f/0x170
> >>  ? set_close_on_exec+0x30/0x70
> >>  vfs_write+0xb5/0x1a0
> >>  SyS_write+0x55/0xc0
> >>  entry_SYSCALL_64_fastpath+0x1a/0xa5
> >> RIP: 0033:0x7f6071bafc20
> >> RSP: 002b:00007ffe7d42ba48 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> >> RAX: ffffffffffffffda RBX: 0000559eca8b0f30 RCX: 00007f6071bafc20
> >> RDX: 0000000000000002 RSI: 0000559eca961f60 RDI: 0000000000000001
> >> RBP: 00007f6071e78ae0 R08: 00007f6071e7a740 R09: 00007f60724b6700
> >> R10: 0000000000000073 R11: 0000000000000246 R12: 0000000000000000
> >> R13: 0000000000000000 R14: 0000000000000000 R15: 0000559eca892170
> >> RIP: pci_iov_add_virtfn+0x2eb/0x350 RSP: ffffb4b2036ebcb8
> >>
> >> The occurs since during AER recovery the ARI Capable Hierarchy bit,
> >> which can affect the values for First VF Offset and VF Stride, is not set
> >> until after pci_iov_set_numvfs() is called.
> >
> > Can you elaborate on where exactly this happens?  The only place we
> > explicitly set PCI_SRIOV_CTRL_ARI is in sriov_init(), which is only
> > called at enumeration-time.  So I'm guessing you're talking about this
> > path:
> >
> >   ixgbe_io_slot_reset
> >     pci_restore_state
> >       pci_restore_iov_state
> >         sriov_restore_state
> >           pci_iov_set_numvfs
> >
> > where we don't set PCI_SRIOV_CTRL_ARI at all.  The fact that you say
> > PCI_SRIOV_CTRL_ARI isn't set until *after* pci_iov_set_numvfs() is
> > called suggests that it is being set *somewhere*, but I don't know
> > where.
> 
> The ARI bit is initialized in sriov_init, stored in iov->ctrl, and
> restored in sriov_restore_state, but it occurs in the line after the
> call to pci_iov_set_numvfs.
> 
> The problem is you don't want to write the full iov->ctrl value until
> after you have reset the the number of VFs since it will set VFE so
> pulling out and configuring the ARI value separately is needed.

Doh, that should have been obvious to me ;)

> >> This can cause the iov
> >> structure to be populated with values that are incorrect if the bit is
> >> later set.   Check and set this bit, if needed, before calling
> >> pci_iov_set_numvfs() so that the values being populated properly take
> >> the ARI bit into account.
> >>
> >> CC: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
> >> CC: Emil Tantilov <emil.s.tantilov@xxxxxxxxx>
> >> Signed-off-by: Tony Nguyen <anthony.l.nguyen@xxxxxxxxx>
> >> ---
> >>  drivers/pci/iov.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> >> index 7492a65..a8896c7 100644
> >> --- a/drivers/pci/iov.c
> >> +++ b/drivers/pci/iov.c
> >> @@ -497,6 +497,10 @@ static void sriov_restore_state(struct pci_dev *dev)
> >>       if (ctrl & PCI_SRIOV_CTRL_VFE)
> >>               return;
> >>
> >> +     if ((iov->ctrl & PCI_SRIOV_CTRL_ARI) && !(ctrl & PCI_SRIOV_CTRL_ARI))
> >> +             pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL,
> >> +                                   ctrl | PCI_SRIOV_CTRL_ARI);

This looks a little fiddly and also assumes that we only ever need to
*set* PCI_SRIOV_CTRL_ARI.  That's likely the case because it's
probably cleared after reset and during resume.  But I'm not *sure*
that's always the case, so what do you think about the proposal below?

> >>       for (i = PCI_IOV_RESOURCES; i <= PCI_IOV_RESOURCE_END; i++)
> >>               pci_update_resource(dev, i);
> >>


commit 95594dedd443e42ab0c16b9fba0109e955e7be13
Author: Tony Nguyen <anthony.l.nguyen@xxxxxxxxx>
Date:   Wed Oct 4 08:52:58 2017 -0700

    PCI: Restore "ARI Capable Hierarchy" before setting numVFs
    
    In the restore path, we previously read PCI_SRIOV_VF_OFFSET and
    PCI_SRIOV_VF_STRIDE before restoring PCI_SRIOV_CTRL_ARI, which
    affects the offset and stride:
    
      pci_restore_state
        pci_restore_iov_state
          sriov_restore_state
            pci_iov_set_numvfs
              pci_read_config_word(... PCI_SRIOV_VF_OFFSET, &iov->offset)
            pci_write_config_word(... PCI_SRIOV_CTRL, iov->ctrl)
    
    The effect is that suspend/resume and AER recovery, which use
    pci_restore_state(), may corrupt iov->offset and iov->stride.  The iov
    state is associated with the device, not the driver, so if we reload the
    driver, it will use the the corrupted data, which may cause crashes like
    this:
    
      kernel BUG at drivers/pci/iov.c:157!
      RIP: 0010:pci_iov_add_virtfn+0x2eb/0x350
      Call Trace:
       pci_enable_sriov+0x353/0x440
       ixgbe_pci_sriov_configure+0xd5/0x1f0 [ixgbe]
       sriov_numvfs_store+0xf7/0x170
       dev_attr_store+0x18/0x30
       sysfs_kf_write+0x37/0x40
       kernfs_fop_write+0x120/0x1b0
       vfs_write+0xb5/0x1a0
       SyS_write+0x55/0xc0
    
    The occurs since during AER recovery the ARI Capable Hierarchy bit, which
    can affect the values for First VF Offset and VF Stride, is not set until
    after pci_iov_set_numvfs() is called.  This can cause the iov structure to
    be populated with values that are incorrect if the bit is later set.
    Check and set this bit, if needed, before calling pci_iov_set_numvfs() so
    that the values being populated properly take the ARI bit into account.
    
    Signed-off-by: Tony Nguyen <anthony.l.nguyen@xxxxxxxxx>
    [bhelgaas: changelog, add comment, also clear ARI if necessary]
    Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
    CC: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
    CC: Emil Tantilov <emil.s.tantilov@xxxxxxxxx>

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index ce24cf235f01..6bacb8995e96 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -498,6 +498,14 @@ static void sriov_restore_state(struct pci_dev *dev)
 	if (ctrl & PCI_SRIOV_CTRL_VFE)
 		return;
 
+	/*
+	 * Restore PCI_SRIOV_CTRL_ARI before pci_iov_set_numvfs() because
+	 * it reads offset & stride, which depend on PCI_SRIOV_CTRL_ARI.
+	 */
+	ctrl &= ~PCI_SRIOV_CTRL_ARI;
+	ctrl |= iov->ctrl & PCI_SRIOV_CTRL_ARI;
+	pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, ctrl);
+
 	for (i = PCI_IOV_RESOURCES; i <= PCI_IOV_RESOURCE_END; i++)
 		pci_update_resource(dev, i);