From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <1455740121.2925.286.camel@hpe.com> Subject: Re: [PATCH] x86/mm: Add x86 valid_phys_addr_range() for /dev/mem From: Toshi Kani Date: Wed, 17 Feb 2016 13:15:21 -0700 In-Reply-To: References: <1455069975-14291-1-git-send-email-toshi.kani@hpe.com> <1455737737.2925.280.camel@hpe.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org To: Dan Williams Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Borislav Petkov , "linux-nvdimm@lists.01.org" , X86 ML , "linux-kernel@vger.kernel.org" List-ID: On Wed, 2016-02-17 at 11:05 -0800, Dan Williams wrote: > On Wed, Feb 17, 2016 at 11:35 AM, Toshi Kani wrote: > > On Wed, 2016-02-17 at 09:58 -0800, Dan Williams wrote: > > > On Tue, Feb 9, 2016 at 6:06 PM, Toshi Kani > > > wrote: > > > > x86 does not define ARCH_HAS_VALID_PHYS_ADDR_RANGE, which > > > > leads /dev/mem to use the default valid_phys_addr_range() > > > > and valid_mmap_phys_addr_range() in drivers/char/mem.c. > > > > > > > > The default valid_phys_addr_range() allows any range lower > > > > than __pa(high_memory), which is the end of system RAM, and > > > > disallows any range higher than it. > > > > > > > > Persistent memory may be located at lower and/or higher > > > > address of __pa(high_memory) depending on their memory slots. > > > > When using crash(8) via /dev/mem for analyzing data in > > > > persistent memory, it can only access to the one lower than > > > > __pa(high_memory). > > > > > > > > Add x86 valid_phys_addr_range() and valid_mmap_phys_addr_range() > > > > to provide better checking: > > > >  - Physical address range is valid when it is fully backed by > > > >    IORESOURCE_MEM, regardless of __pa(high_memory). > > > >  - Other ranges, including holes, are invalid. > > > > > > > > This also allows crash(8) to access persistent memory ranges > > > > via /dev/mem (with a minor change to remove high_memory check > > > > from crash itself). > > > > > > If we're modifying crash(8) can't we also teach it to mmap /dev/pmemX > > > directly?  With commit 90a545e98126 "restrict /dev/mem to idle io > > > memory ranges" /dev/mem should not have access to active pmem ranges. > > > > Yes, I am aware of the commit.  Unloading drivers while using crash(8) > > to analyze NVDIMM via /dev/mem makes sense.  /dev/mem does not require > > any other drivers be loaded. > > Ah, ok.  I thought this patch was bypassing that safety check.  If it > requires the driver to be unloaded first then I'm fine with this. Yes, crash(8) is used for analyzing static data (such as a crashdump file).  It does not allow writing data unless user specifically enable it. > > Using /dev/pmemX, on the other hand, requires the driver to be loaded, > > which can be problematic.  For instance, when btt_init() fails due to > > some corruption in arena, it fails to create any pmem device file.  A > > dev file also restricts access range within the dev file. > > > > Thanks, > > -Toshi > > > > ps. > > Looking at iomem_is_exclusive(), it only checks the top-level iomem > > entries.  I think the pmem/btt driver only marks a child entry busy... > > > > It looks to me that next_resource(), via r_next(), walks child ranges. Oh, sorry, I missed the r_next(). Thanks, -Toshi