Zou Nan hai (on 11 Sep 2006 14:12:13 +0800) wrote: > For 2.6 kernel, I think GP is a region 5 address when inside kernel. >The entire kernel image is resided in region 5 without relocate to >region 7. You are right, I have only three excuses. (1) Having too much fun skiing to think about computers. (2) The kernel _used_ to be in region 7. (3) The kernel addresses in region 5 can always be accessed via the identity map in region 7 and sometimes we do just that, see below. > Another issue I can see from calculate GP from physical address passed >from OS_INIT is, > I am not quite sure though, if OS_INIT is happened during a module >execution, or happened when system is in user space, what GP value will >be passed from SAL/PAL? If the gp value is the physical address of the >modules 's gp, we can't set GP value according to that, because >ia64_init_handler is inside kernel. It does not matter where the kernel was when the INIT was delivered, even if the INIT ws delivered while a module was in control. r1 must be loaded with the correct gp for the kernel, because ia64_init_handler is a kernel routine, not a module routine. The sequence goes :- * Kernel boots * ia64_mca_init() -> ia64_sal_set_vectors(), passing the _physical_ value of the kernel's gp. This physical address is derived from the region 5 virtual gp by tpa(). * Kernel runs. INIT is delivered. It does not matter what state the machine is in, in kernel, a module or PAL/SAL is irrelevant. * ia64_os_init_dispatch() -> ia64_set_kernel_registers() which converts the physical gp to a region 7 identity mapped virtual gp. * ia64_os_init_dispatch() -> ia64_init_handler(). * ia64_init_handler() runs using a region 7 virtual gp. This is a different virtual address than the original region 5 gp that the kernel booted with, but both the region 5 and region 7 gp values map the same physical pages. > Kexec kernel used in kdump is usually exactly the same kernel with the >host kernel, except they are located in different physical address >ranges. The first kernel will never touch the RAM belongs to the crash >kernel at run time. The crash kernel will not touch the RAM belongs to >the first kernel unless you read it via /proc/vmcore. Which means that the region 7 gp used by MCA/INIT is no good for the kexec kernel. You either need the original region 5 gp or you need to adjust r1 by the difference between the physical start of the real kernel and the physical start of the kexec kernel. Note: When I did the code in ia64_set_kernel_registers(), it was too messy to work out what the original region 5 gp value was, so I just did 'DATA_PA_TO_VA(r1,temp1)' and relied on the identity mapping in region 7. Perhaps the correct fix is for ia64_set_kernel_registers() to set the correct region 5 gp and not rely on the identity mapping. That should easy enough to do, define a global variable that contains the region 5 value of gp and load that value in ia64_set_kernel_registers instead of using DATA_PA_TO_VA. - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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