Re: [PATCH v3 14/16] resource: Move devmem revoke code to resource framework

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Wed, Oct 21, 2020 at 8:59 PM Dan Williams <dan.j.williams@intel.com> wrote:
>
> On Wed, Oct 21, 2020 at 1:57 AM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> >
> > We want all iomem mmaps to consistently revoke ptes when the kernel
> > takes over and CONFIG_IO_STRICT_DEVMEM is enabled. This includes the
> > pci bar mmaps available through procfs and sysfs, which currently do
> > not revoke mappings.
> >
> > To prepare for this, move the code from the /dev/kmem driver to
> > kernel/resource.c.
> >
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: John Hubbard <jhubbard@nvidia.com>
> > Cc: Jérôme Glisse <jglisse@redhat.com>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: linux-mm@kvack.org
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-samsung-soc@vger.kernel.org
> > Cc: linux-media@vger.kernel.org
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: David Hildenbrand <david@redhat.com>
> > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.com>
> > --
> > v3:
> > - add barrier for consistency and document why we don't have to check
> >   for NULL (Jason)
> > ---
> >  drivers/char/mem.c     |  85 +---------------------------------
> >  include/linux/ioport.h |   6 +--
> >  kernel/resource.c      | 101 ++++++++++++++++++++++++++++++++++++++++-
> >  3 files changed, 102 insertions(+), 90 deletions(-)
> >
> > diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> > index 5502f56f3655..53338aad8d28 100644
> > --- a/drivers/char/mem.c
> > +++ b/drivers/char/mem.c
> > @@ -31,9 +31,6 @@
> >  #include <linux/uio.h>
> >  #include <linux/uaccess.h>
> >  #include <linux/security.h>
> > -#include <linux/pseudo_fs.h>
> > -#include <uapi/linux/magic.h>
> > -#include <linux/mount.h>
> >
> >  #ifdef CONFIG_IA64
> >  # include <linux/efi.h>
> > @@ -809,42 +806,6 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
> >         return ret;
> >  }
> >
> > -static struct inode *devmem_inode;
> > -
> > -#ifdef CONFIG_IO_STRICT_DEVMEM
> > -void revoke_devmem(struct resource *res)
> > -{
> > -       /* pairs with smp_store_release() in devmem_init_inode() */
> > -       struct inode *inode = smp_load_acquire(&devmem_inode);
> > -
> > -       /*
> > -        * Check that the initialization has completed. Losing the race
> > -        * is ok because it means drivers are claiming resources before
> > -        * the fs_initcall level of init and prevent /dev/mem from
> > -        * establishing mappings.
> > -        */
> > -       if (!inode)
> > -               return;
> > -
> > -       /*
> > -        * The expectation is that the driver has successfully marked
> > -        * the resource busy by this point, so devmem_is_allowed()
> > -        * should start returning false, however for performance this
> > -        * does not iterate the entire resource range.
> > -        */
> > -       if (devmem_is_allowed(PHYS_PFN(res->start)) &&
> > -           devmem_is_allowed(PHYS_PFN(res->end))) {
> > -               /*
> > -                * *cringe* iomem=relaxed says "go ahead, what's the
> > -                * worst that can happen?"
> > -                */
> > -               return;
> > -       }
> > -
> > -       unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
> > -}
> > -#endif
> > -
> >  static int open_port(struct inode *inode, struct file *filp)
> >  {
> >         int rc;
> > @@ -864,7 +825,7 @@ static int open_port(struct inode *inode, struct file *filp)
> >          * revocations when drivers want to take over a /dev/mem mapped
> >          * range.
> >          */
> > -       filp->f_mapping = inode->i_mapping;
> > +       filp->f_mapping = iomem_get_mapping();
> >
> >         return 0;
> >  }
> > @@ -995,48 +956,6 @@ static char *mem_devnode(struct device *dev, umode_t *mode)
> >
> >  static struct class *mem_class;
> >
> > -static int devmem_fs_init_fs_context(struct fs_context *fc)
> > -{
> > -       return init_pseudo(fc, DEVMEM_MAGIC) ? 0 : -ENOMEM;
> > -}
> > -
> > -static struct file_system_type devmem_fs_type = {
> > -       .name           = "devmem",
> > -       .owner          = THIS_MODULE,
> > -       .init_fs_context = devmem_fs_init_fs_context,
> > -       .kill_sb        = kill_anon_super,
> > -};
> > -
> > -static int devmem_init_inode(void)
> > -{
> > -       static struct vfsmount *devmem_vfs_mount;
> > -       static int devmem_fs_cnt;
> > -       struct inode *inode;
> > -       int rc;
> > -
> > -       rc = simple_pin_fs(&devmem_fs_type, &devmem_vfs_mount, &devmem_fs_cnt);
> > -       if (rc < 0) {
> > -               pr_err("Cannot mount /dev/mem pseudo filesystem: %d\n", rc);
> > -               return rc;
> > -       }
> > -
> > -       inode = alloc_anon_inode(devmem_vfs_mount->mnt_sb);
> > -       if (IS_ERR(inode)) {
> > -               rc = PTR_ERR(inode);
> > -               pr_err("Cannot allocate inode for /dev/mem: %d\n", rc);
> > -               simple_release_fs(&devmem_vfs_mount, &devmem_fs_cnt);
> > -               return rc;
> > -       }
> > -
> > -       /*
> > -        * Publish /dev/mem initialized.
> > -        * Pairs with smp_load_acquire() in revoke_devmem().
> > -        */
> > -       smp_store_release(&devmem_inode, inode);
> > -
> > -       return 0;
> > -}
> > -
> >  static int __init chr_dev_init(void)
> >  {
> >         int minor;
> > @@ -1058,8 +977,6 @@ static int __init chr_dev_init(void)
> >                  */
> >                 if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
> >                         continue;
> > -               if ((minor == DEVMEM_MINOR) && devmem_init_inode() != 0)
> > -                       continue;
> >
> >                 device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
> >                               NULL, devlist[minor].name);
> > diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> > index 6c2b06fe8beb..8ffb61b36606 100644
> > --- a/include/linux/ioport.h
> > +++ b/include/linux/ioport.h
> > @@ -302,11 +302,7 @@ struct resource *devm_request_free_mem_region(struct device *dev,
> >  struct resource *request_free_mem_region(struct resource *base,
> >                 unsigned long size, const char *name);
> >
> > -#ifdef CONFIG_IO_STRICT_DEVMEM
> > -void revoke_devmem(struct resource *res);
> > -#else
> > -static inline void revoke_devmem(struct resource *res) { };
> > -#endif
> > +extern struct address_space *iomem_get_mapping(void);
> >
> >  #endif /* __ASSEMBLY__ */
> >  #endif /* _LINUX_IOPORT_H */
> > diff --git a/kernel/resource.c b/kernel/resource.c
> > index 841737bbda9e..a92fed5b9997 100644
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> > @@ -18,12 +18,15 @@
> >  #include <linux/spinlock.h>
> >  #include <linux/fs.h>
> >  #include <linux/proc_fs.h>
> > +#include <linux/pseudo_fs.h>
> >  #include <linux/sched.h>
> >  #include <linux/seq_file.h>
> >  #include <linux/device.h>
> >  #include <linux/pfn.h>
> >  #include <linux/mm.h>
> > +#include <linux/mount.h>
> >  #include <linux/resource_ext.h>
> > +#include <uapi/linux/magic.h>
> >  #include <asm/io.h>
> >
> >
> > @@ -1112,6 +1115,58 @@ resource_size_t resource_alignment(struct resource *res)
> >
> >  static DECLARE_WAIT_QUEUE_HEAD(muxed_resource_wait);
> >
> > +static struct inode *iomem_inode;
> > +
> > +#ifdef CONFIG_IO_STRICT_DEVMEM
> > +static void revoke_iomem(struct resource *res)
> > +{
> > +       /* pairs with smp_store_release() in iomem_init_inode() */
> > +       struct inode *inode = smp_load_acquire(&iomem_inode);
> > +
> > +       /*
> > +        * Check that the initialization has completed. Losing the race
> > +        * is ok because it means drivers are claiming resources before
> > +        * the fs_initcall level of init and prevent /dev/mem from
>
> How about:
>
> s,/dev/mem,iomem_get_mapping() users,
>
> ...now that this facility is generalized?
>
> > +        * establishing mappings.
> > +        */
> > +       if (!inode)
> > +               return;
> > +
> > +       /*
> > +        * The expectation is that the driver has successfully marked
> > +        * the resource busy by this point, so devmem_is_allowed()
> > +        * should start returning false, however for performance this
> > +        * does not iterate the entire resource range.
> > +        */
> > +       if (devmem_is_allowed(PHYS_PFN(res->start)) &&
> > +           devmem_is_allowed(PHYS_PFN(res->end))) {
> > +               /*
> > +                * *cringe* iomem=relaxed says "go ahead, what's the
> > +                * worst that can happen?"
> > +                */
> > +               return;
> > +       }
> > +
> > +       unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1);
> > +}
> > +struct address_space *iomem_get_mapping(void)
> > +{
> > +       /*
> > +        * This function is only called from file open paths, hence guaranteed
> > +        * that fs_initcalls have completed and no need to check for NULL. But
> > +        * since revoke_iomem can be called before the initcall we still need
> > +        * the barrier to appease checkers.
> > +        */
> > +       return smp_load_acquire(&iomem_inode)->i_mapping;
> > +}
> > +#else
> > +static void revoke_iomem(struct resource *res) {}
> > +struct address_space *iomem_get_mapping(void)
> > +{
> > +       return NULL;
> > +}
> > +#endif
> > +
> >  /**
> >   * __request_region - create a new busy resource region
> >   * @parent: parent resource descriptor
> > @@ -1179,7 +1234,7 @@ struct resource * __request_region(struct resource *parent,
> >         write_unlock(&resource_lock);
> >
> >         if (res && orig_parent == &iomem_resource)
> > -               revoke_devmem(res);
> > +               revoke_iomem(res);
> >
> >         return res;
> >  }
> > @@ -1713,4 +1768,48 @@ static int __init strict_iomem(char *str)
> >         return 1;
> >  }
> >
> > +static int iomem_fs_init_fs_context(struct fs_context *fc)
> > +{
> > +       return init_pseudo(fc, DEVMEM_MAGIC) ? 0 : -ENOMEM;
> > +}
> > +
> > +static struct file_system_type iomem_fs_type = {
> > +       .name           = "iomem",
> > +       .owner          = THIS_MODULE,
> > +       .init_fs_context = iomem_fs_init_fs_context,
> > +       .kill_sb        = kill_anon_super,
> > +};
> > +
> > +static int __init iomem_init_inode(void)
> > +{
> > +       static struct vfsmount *iomem_vfs_mount;
> > +       static int iomem_fs_cnt;
> > +       struct inode *inode;
> > +       int rc;
> > +
> > +       rc = simple_pin_fs(&iomem_fs_type, &iomem_vfs_mount, &iomem_fs_cnt);
> > +       if (rc < 0) {
> > +               pr_err("Cannot mount iomem pseudo filesystem: %d\n", rc);
> > +               return rc;
> > +       }
> > +
> > +       inode = alloc_anon_inode(iomem_vfs_mount->mnt_sb);
> > +       if (IS_ERR(inode)) {
> > +               rc = PTR_ERR(inode);
> > +               pr_err("Cannot allocate inode for iomem: %d\n", rc);
> > +               simple_release_fs(&iomem_vfs_mount, &iomem_fs_cnt);
> > +               return rc;
> > +       }
> > +
> > +       /*
> > +        * Publish /dev/mem initialized.
>
> Similar potential fixup:
>
> "Publish iomem revocation inode initialized"

Yeah makes sense I fix up the comments, I'll do that in v4. Need to
fix up my mangeld sob line anyway :-)

Thanks for taking a careful look at this!

Cheers, Daniel

> Other than that:
>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch