Messages in this thread | | | Date | Wed, 17 Feb 2016 11:05:27 -0800 | Subject | Re: [PATCH] x86/mm: Add x86 valid_phys_addr_range() for /dev/mem | From | Dan Williams <> |
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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.
> 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.
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