From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Williams Subject: Re: [PATCH 1/6] pmem: add force casts to avoid __iomem annotation Date: Fri, 29 May 2015 05:53:00 -0700 Message-ID: References: <1432852553-24865-1-git-send-email-ross.zwisler@linux.intel.com> <1432852553-24865-2-git-send-email-ross.zwisler@linux.intel.com> <1432899584.4282.2.camel@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: Received: from mail-wg0-f47.google.com ([74.125.82.47]:33677 "EHLO mail-wg0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753184AbbE2MxB (ORCPT ); Fri, 29 May 2015 08:53:01 -0400 Received: by wgez8 with SMTP id z8so61852490wge.0 for ; Fri, 29 May 2015 05:53:00 -0700 (PDT) In-Reply-To: <1432899584.4282.2.camel@gmail.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Ross Zwisler Cc: Ross Zwisler , Linux ACPI , "linux-kernel@vger.kernel.org" , "linux-nvdimm@lists.01.org" On Fri, May 29, 2015 at 4:39 AM, Ross Zwisler wrote: > On Thu, 2015-05-28 at 15:47 -0700, Dan Williams wrote: >> On Thu, May 28, 2015 at 3:35 PM, Ross Zwisler >> 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 >> > Cc: Dan Williams >> > 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.