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

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