RE: [PATCH v3 08/10] vfio/pci: protect cap/ecap_perm bits alloc/free

[Liu, Yi L]

> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: Monday, December 16, 2019 6:47 AM
> To: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Subject: Re: [PATCH v3 08/10] vfio/pci: protect cap/ecap_perm bits alloc/free
> 
> On Thu, 21 Nov 2019 19:23:45 +0800
> Liu Yi L <yi.l.liu@xxxxxxxxx> wrote:
> 
> > This patch add a user numer track for the shared cap/ecap_perms bits,
> > and the alloc/free will hold a semaphore to protect the operations.
> > With the changes, first caller of vfio_pci_init_perm_bits() will
> > initialize the bits. While the last caller of vfio_pci_uninit_perm_bits()
> > will free the bits. This is a preparation to have multiple cap/ecap_perms
> > bits users.
> >
> > Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> > Cc: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > ---
> >  drivers/vfio/pci/vfio_pci_config.c | 33 +++++++++++++++++++++++++++++++--
> >  1 file changed, 31 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> > index f0891bd..274c993 100644
> > --- a/drivers/vfio/pci/vfio_pci_config.c
> > +++ b/drivers/vfio/pci/vfio_pci_config.c
> > @@ -36,6 +36,13 @@
> >  	 (offset >= PCI_ROM_ADDRESS && offset < PCI_ROM_ADDRESS + 4))
> >
> >  /*
> > + * vfio_perm_bits_sem: prorects the shared perm_bits alloc/free
> > + * vfio_pci_perm_bits_users: tracks the user of the shared perm_bits
> > + */
> > +static DEFINE_SEMAPHORE(vfio_perm_bits_sem);
> > +static int vfio_pci_perm_bits_users;
> > +
> > +/*
> >   * Lengths of PCI Config Capabilities
> >   *   0: Removed from the user visible capability list
> >   *   FF: Variable length
> > @@ -995,7 +1002,7 @@ static int __init init_pci_ext_cap_pwr_perm(struct
> perm_bits *perm)
> >  /*
> >   * Initialize the shared permission tables
> >   */
> > -void vfio_pci_uninit_perm_bits(void)
> > +static void vfio_pci_uninit_perm_bits_internal(void)
> >  {
> >  	free_perm_bits(&cap_perms[PCI_CAP_ID_BASIC]);
> >
> > @@ -1009,10 +1016,30 @@ void vfio_pci_uninit_perm_bits(void)
> >  	free_perm_bits(&ecap_perms[PCI_EXT_CAP_ID_PWR]);
> >  }
> >
> > +void vfio_pci_uninit_perm_bits(void)
> > +{
> > +	down(&vfio_perm_bits_sem);
> > +
> > +	if (--vfio_pci_perm_bits_users > 0)
> > +		goto out;
> > +
> > +	vfio_pci_uninit_perm_bits_internal();
> > +
> > +out:
> > +	up(&vfio_perm_bits_sem);
> > +}
> > +
> >  int __init vfio_pci_init_perm_bits(void)
> >  {
> >  	int ret;
> >
> > +	down(&vfio_perm_bits_sem);
> > +
> > +	if (++vfio_pci_perm_bits_users > 1) {
> > +		ret = 0;
> > +		goto out;
> > +	}
> > +
> >  	/* Basic config space */
> >  	ret = init_pci_cap_basic_perm(&cap_perms[PCI_CAP_ID_BASIC]);
> >
> > @@ -1030,8 +1057,10 @@ int __init vfio_pci_init_perm_bits(void)
> >  	ecap_perms[PCI_EXT_CAP_ID_VNDR].writefn = vfio_raw_config_write;
> >
> >  	if (ret)
> > -		vfio_pci_uninit_perm_bits();
> > +		vfio_pci_uninit_perm_bits_internal();
> >
> > +out:
> > +	up(&vfio_perm_bits_sem);
> >  	return ret;
> >  }
> >
> 
> Hi Yi,
> 
> Sorry for slowness in providing feedback on this series.  If we
> provided a vfio-pci-common module that vfio-pci and vfio-mdev-pci
> depend on, doesn't this entire problem go away? 

I checked previous email, export the common functions out of
vfio-pci module was proposed in RFC v2. But at that time, I didn't
propose to have a separate module. So I guess it may be just correct
way. Below is the reply at that time.

https://lkml.org/lkml/2019/3/19/756

> I played a little bit
> with this in the crude patch below, it seems to work.  To finish this,
> I think we'd move the function declarations out of the "private" header
> file and into one under include/linux, then we could also move
> vfio_mdev_pci.c to the samples directory like we intended originally.
> I know you had tried to link things from samples and it didn't work,
> but is the below a better attempt at resolving this?  It commits us to
> exporting a bunch of functions, we'll need to decide whether that's a
> good idea.  Thanks,

I played with your patch and added a crude patch to move
vfio-mdev-pci to samples directory. I can see below errors with
either CONFIG_VFIO_PCI_COMMON=y and
CONFIG_SAMPLE_VFIO_MDEV_PCI=y, or
CONFIG_VFIO_PCI_COMMON=m and
CONFIG_SAMPLE_VFIO_MDEV_PCI=m.

But CONFIG_VFIO_PCI_COMMON works well with CONFIG_VFIO_PCI...

Kernel: arch/x86/boot/bzImage is ready  (#88)
ERROR: "vfio_pci_fill_ids" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_err_handlers" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_reflck_attach" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_write" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_disable" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_reflck_put" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_refresh_config" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_set_power_state" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_enable" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_set_vga_decode" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_probe_power_state" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_mmap" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_ioctl" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
ERROR: "vfio_pci_read" [samples/vfio-mdev-pci/vfio-mdev-pci.ko] undefined!
scripts/Makefile.modpost:93: recipe for target '__modpost' failed

So I'm afraid that it still cannot resolve the problem which we encountered
when trying to place vfio-mdev-pci in samples/.

Regards,
Yi Liu

================= [the crude patch] =================