On Thu, 23 Jan 2014, Russell King - ARM Linux wrote: > On Thu, Jan 23, 2014 at 02:15:07PM -0500, Nicolas Pitre wrote: > > On Wed, 22 Jan 2014, Wang Nan wrote: > > > > > This patch allows the kernel to be loaded at the middle of kernel awared > > > physical memory. Before this patch, users must use mem= or device tree to cheat > > > kernel about the start address of physical memory. > > > > > > This feature is useful in some special cases, for example, building a crash > > > dump kernel. Without it, kernel command line, atag and devicetree must be > > > adjusted carefully, sometimes is impossible. > > > > With CONFIG_PATCH_PHYS_VIRT the value for PHYS_OFFSET is determined > > dynamically by rounding down the kernel image start address to the > > previous 16MB boundary. In the case of a crash kernel, this might be > > cleaner to simply readjust __pv_phys_offset during early boot and call > > fixup_pv_table(), and then reserve away the memory from the previous > > kernel. That will let you access that memory directly (with gdb for > > example) and no pointer address translation will be required. > > We already have support in the kernel to ignore memory below the calculated > PHYS_OFFSET. See 571b14375019c3a66ef70d4d4a7083f4238aca30. Sure. Anyway what I'm suggesting above would require that the crash kernel be linked at a different virtual address for that to work. That's probably more trouble than simply mapping the otherwise still unmapped memory from the crashed kernel. Nicolas
