Messages in this thread | | | 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 |
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On Wed, 2016-02-17 at 11:05 -0800, Dan Williams wrote: > On Wed, Feb 17, 2016 at 11:35 AM, Toshi Kani <toshi.kani@hpe.com> wrote: > > On Wed, 2016-02-17 at 09:58 -0800, Dan Williams wrote: > > > On Tue, Feb 9, 2016 at 6:06 PM, Toshi Kani <toshi.kani@hpe.com> > > > 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
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