On Wed, 2016-02-17 at 09:58 -0800, Dan Williams wrote: > On Tue, Feb 9, 2016 at 6:06 PM, Toshi Kani <[email protected]> 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. 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...
