On Fri, May 29, 2015 at 5:53 AM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > On Fri, May 29, 2015 at 4:39 AM, Ross Zwisler <zwisler@xxxxxxxxx> 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@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> >>> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> >>> > Cc: linux-nvdimm@xxxxxxxxxxxx >>> > --- >>> > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
