diff mbox

[1/6] pmem: add force casts to avoid __iomem annotation

Message ID 1432852553-24865-2-git-send-email-ross.zwisler@linux.intel.com
State Superseded
Headers show

Commit Message

Ross Zwisler May 28, 2015, 10:35 p.m. UTC
Even though we use ioremap_nocache() to map our persistent memory in the
pmem driver, the memory we are mapping behaves like normal memory and
not I/O memory in that it can be accessed using regular memcpy()
operations and doesn't need to go through memcpy_toio() and
memcpy_fromio().  Force casting the pointers received from
ioremap_nocache() and given to iounmap() gives us the correct behavior
and makes sparse happy.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: linux-nvdimm@lists.01.org
---
 drivers/block/nd/pmem.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Comments

Dan Williams May 28, 2015, 10:47 p.m. UTC | #1
On Thu, May 28, 2015 at 3:35 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> Even though we use ioremap_nocache() to map our persistent memory in the
> pmem driver, the memory we are mapping behaves like normal memory and
> not I/O memory in that it can be accessed using regular memcpy()
> operations and doesn't need to go through memcpy_toio() and
> memcpy_fromio().  Force casting the pointers received from
> ioremap_nocache() and given to iounmap() gives us the correct behavior
> and makes sparse happy.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: linux-nvdimm@lists.01.org
> ---
>  drivers/block/nd/pmem.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/nd/pmem.c b/drivers/block/nd/pmem.c
> index 5e8c9c629f22..a8712e41e7f5 100644
> --- a/drivers/block/nd/pmem.c
> +++ b/drivers/block/nd/pmem.c
> @@ -163,7 +163,8 @@ static struct pmem_device *pmem_alloc(struct device *dev, struct resource *res,
>          * of the CPU caches in case of a crash.
>          */
>         err = -ENOMEM;
> -       pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem->size);
> +       pmem->virt_addr = (__force void *)ioremap_nocache(pmem->phys_addr,
> +                       pmem->size);

I think I'd rather see casting when ->virt_addr is used (the
__io_virt() helper can be used to make this a tad cleaner), or provide
ioremap apis that don't attach __iomem to their return value.  Because
in this and other cases ioremap() is being on non "i/o" memory.
Ross Zwisler May 29, 2015, 11:39 a.m. UTC | #2
On Thu, 2015-05-28 at 15:47 -0700, Dan Williams wrote:
> On Thu, May 28, 2015 at 3:35 PM, Ross Zwisler
> <ross.zwisler@linux.intel.com> wrote:
> > Even though we use ioremap_nocache() to map our persistent memory 
> > in the
> > pmem driver, the memory we are mapping behaves like normal memory 
> > and
> > not I/O memory in that it can be accessed using regular memcpy()
> > operations and doesn't need to go through memcpy_toio() and
> > memcpy_fromio().  Force casting the pointers received from
> > ioremap_nocache() and given to iounmap() gives us the correct 
> > behavior
> > and makes sparse happy.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: linux-nvdimm@lists.01.org
> > ---
> >  drivers/block/nd/pmem.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/block/nd/pmem.c b/drivers/block/nd/pmem.c
> > index 5e8c9c629f22..a8712e41e7f5 100644
> > --- a/drivers/block/nd/pmem.c
> > +++ b/drivers/block/nd/pmem.c
> > @@ -163,7 +163,8 @@ static struct pmem_device *pmem_alloc(struct 
> > device *dev, struct resource *res,
> >          * of the CPU caches in case of a crash.
> >          */
> >         err = -ENOMEM;
> > -       pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem
> > ->size);
> > +       pmem->virt_addr = (__force void *)ioremap_nocache(pmem
> > ->phys_addr,
> > +                       pmem->size);
> 
> I think I'd rather see casting when ->virt_addr is used (the
> __io_virt() helper can be used to make this a tad cleaner), or 
> provide
> ioremap apis that don't attach __iomem to their return value. 
>  Because
> in this and other cases ioremap() is being on non "i/o" memory.

The reason that I thought this was cleaner was that now when you look
at the pmem->virt_addr definition it is just a clean void* with no
annotations.  This correctly describes the memory to the user (it's
usable as regular memory, it's in the kernel address space, etc.).

Having the pointer itself annotated with __iomem feels weird to me
because a random well meaning user could incorrectly try to use it as
I/O memory.
Dan Williams May 29, 2015, 12:53 p.m. UTC | #3
On Fri, May 29, 2015 at 4:39 AM, Ross Zwisler <zwisler@gmail.com> wrote:
> On Thu, 2015-05-28 at 15:47 -0700, Dan Williams wrote:
>> On Thu, May 28, 2015 at 3:35 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
>> > Even though we use ioremap_nocache() to map our persistent memory
>> > in the
>> > pmem driver, the memory we are mapping behaves like normal memory
>> > and
>> > not I/O memory in that it can be accessed using regular memcpy()
>> > operations and doesn't need to go through memcpy_toio() and
>> > memcpy_fromio().  Force casting the pointers received from
>> > ioremap_nocache() and given to iounmap() gives us the correct
>> > behavior
>> > and makes sparse happy.
>> >
>> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
>> > Cc: Dan Williams <dan.j.williams@intel.com>
>> > Cc: linux-nvdimm@lists.01.org
>> > ---
>> >  drivers/block/nd/pmem.c | 7 ++++---
>> >  1 file changed, 4 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/drivers/block/nd/pmem.c b/drivers/block/nd/pmem.c
>> > index 5e8c9c629f22..a8712e41e7f5 100644
>> > --- a/drivers/block/nd/pmem.c
>> > +++ b/drivers/block/nd/pmem.c
>> > @@ -163,7 +163,8 @@ static struct pmem_device *pmem_alloc(struct
>> > device *dev, struct resource *res,
>> >          * of the CPU caches in case of a crash.
>> >          */
>> >         err = -ENOMEM;
>> > -       pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem
>> > ->size);
>> > +       pmem->virt_addr = (__force void *)ioremap_nocache(pmem
>> > ->phys_addr,
>> > +                       pmem->size);
>>
>> I think I'd rather see casting when ->virt_addr is used (the
>> __io_virt() helper can be used to make this a tad cleaner), or
>> provide
>> ioremap apis that don't attach __iomem to their return value.
>>  Because
>> in this and other cases ioremap() is being on non "i/o" memory.
>
> The reason that I thought this was cleaner was that now when you look
> at the pmem->virt_addr definition it is just a clean void* with no
> annotations.  This correctly describes the memory to the user (it's
> usable as regular memory, it's in the kernel address space, etc.).
>
> Having the pointer itself annotated with __iomem feels weird to me
> because a random well meaning user could incorrectly try to use it as
> I/O memory.

pmem->virt_addr does not leak outside the driver to random well
meaning users.  I think we have two options, provide physical address
remap helpers from the outset (memremap()?) that don't attach __iomem,
or put the casts on the non-iomem usages.
Dan Williams May 29, 2015, 1:22 p.m. UTC | #4
On Fri, May 29, 2015 at 5:53 AM, Dan Williams <dan.j.williams@intel.com> wrote:
> On Fri, May 29, 2015 at 4:39 AM, Ross Zwisler <zwisler@gmail.com> wrote:
>> On Thu, 2015-05-28 at 15:47 -0700, Dan Williams wrote:
>>> On Thu, May 28, 2015 at 3:35 PM, Ross Zwisler
>>> <ross.zwisler@linux.intel.com> wrote:
>>> > Even though we use ioremap_nocache() to map our persistent memory
>>> > in the
>>> > pmem driver, the memory we are mapping behaves like normal memory
>>> > and
>>> > not I/O memory in that it can be accessed using regular memcpy()
>>> > operations and doesn't need to go through memcpy_toio() and
>>> > memcpy_fromio().  Force casting the pointers received from
>>> > ioremap_nocache() and given to iounmap() gives us the correct
>>> > behavior
>>> > and makes sparse happy.
>>> >
>>> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
>>> > Cc: Dan Williams <dan.j.williams@intel.com>
>>> > Cc: linux-nvdimm@lists.01.org
>>> > ---
>>> >  drivers/block/nd/pmem.c | 7 ++++---
>>> >  1 file changed, 4 insertions(+), 3 deletions(-)
>>> >
>>> > diff --git a/drivers/block/nd/pmem.c b/drivers/block/nd/pmem.c
>>> > index 5e8c9c629f22..a8712e41e7f5 100644
>>> > --- a/drivers/block/nd/pmem.c
>>> > +++ b/drivers/block/nd/pmem.c
>>> > @@ -163,7 +163,8 @@ static struct pmem_device *pmem_alloc(struct
>>> > device *dev, struct resource *res,
>>> >          * of the CPU caches in case of a crash.
>>> >          */
>>> >         err = -ENOMEM;
>>> > -       pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem
>>> > ->size);
>>> > +       pmem->virt_addr = (__force void *)ioremap_nocache(pmem
>>> > ->phys_addr,
>>> > +                       pmem->size);
>>>
>>> I think I'd rather see casting when ->virt_addr is used (the
>>> __io_virt() helper can be used to make this a tad cleaner), or
>>> provide
>>> ioremap apis that don't attach __iomem to their return value.
>>>  Because
>>> in this and other cases ioremap() is being on non "i/o" memory.
>>
>> The reason that I thought this was cleaner was that now when you look
>> at the pmem->virt_addr definition it is just a clean void* with no
>> annotations.  This correctly describes the memory to the user (it's
>> usable as regular memory, it's in the kernel address space, etc.).
>>
>> Having the pointer itself annotated with __iomem feels weird to me
>> because a random well meaning user could incorrectly try to use it as
>> I/O memory.
>
> pmem->virt_addr does not leak outside the driver to random well
> meaning users.  I think we have two options, provide physical address
> remap helpers from the outset (memremap()?) that don't attach __iomem,
> or put the casts on the non-iomem usages.

In other words, I don't like the fact that we apply a coarse / private
hack to fix a general kernel mis-annotation problem.  Either fix it
for everybody with something like memremap() or use __io_virt() to
document the non-iomem usages of pmem->virt_addr like the other
iomem-to-undecorated pointer helper routines in the kernel.
diff mbox

Patch

diff --git a/drivers/block/nd/pmem.c b/drivers/block/nd/pmem.c
index 5e8c9c629f22..a8712e41e7f5 100644
--- a/drivers/block/nd/pmem.c
+++ b/drivers/block/nd/pmem.c
@@ -163,7 +163,8 @@  static struct pmem_device *pmem_alloc(struct device *dev, struct resource *res,
 	 * of the CPU caches in case of a crash.
 	 */
 	err = -ENOMEM;
-	pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem->size);
+	pmem->virt_addr = (__force void *)ioremap_nocache(pmem->phys_addr,
+			pmem->size);
 	if (!pmem->virt_addr)
 		goto out_release_region;
 
@@ -195,7 +196,7 @@  static struct pmem_device *pmem_alloc(struct device *dev, struct resource *res,
 out_free_queue:
 	blk_cleanup_queue(pmem->pmem_queue);
 out_unmap:
-	iounmap(pmem->virt_addr);
+	iounmap((__force void __iomem *)pmem->virt_addr);
 out_release_region:
 	release_mem_region(pmem->phys_addr, pmem->size);
 out_free_dev:
@@ -209,7 +210,7 @@  static void pmem_free(struct pmem_device *pmem)
 	del_gendisk(pmem->pmem_disk);
 	put_disk(pmem->pmem_disk);
 	blk_cleanup_queue(pmem->pmem_queue);
-	iounmap(pmem->virt_addr);
+	iounmap((__force void __iomem *)pmem->virt_addr);
 	release_mem_region(pmem->phys_addr, pmem->size);
 	kfree(pmem);
 }