On Wed, 2008-05-14 at 16:52 -0400, Vivek Goyal wrote: [...] > Ok, I have done some testing on this patch. Currently I have just > tested switching back and forth between two kernels and it is working for > me. Thanks. [...] > > +/* > > + * Entry point for jumping back from kexeced kernel, the paging is > > + * turned off. > > + */ > > +kexec_jump_back_entry: > > + call 1f > > +1: > > + popl %ebx > > + subl $(1b - kexec_relocate_page), %ebx > > + movl %edi, KJUMP_ENTRY_OFF(%ebx) > > + movl CP_VA_CONTROL_PAGE(%ebx), %edi > > + lea STACK_TOP(%ebx), %esp > > + movl CP_PA_SWAP_PAGE(%ebx), %eax > > + movl CP_PA_BACKUP_PAGES_MAP(%ebx), %edx > > + pushl %eax > > + pushl %edx > > + call swap_pages > > + addl $8, %esp > > + movl CP_PA_PGD(%ebx), %eax > > + movl %eax, %cr3 > > + movl %cr0, %eax > > + orl $(1<<31), %eax > > + movl %eax, %cr0 > > + lea STACK_TOP(%edi), %esp > > + movl %edi, %eax > > + addl $(virtual_mapped - kexec_relocate_page), %eax > > + pushl %eax > > + ret > > Upon re-entering the kernel, what happens to GDT table? So gdtr will be > pointing to GDT of other kernel (which is not there as pages have been > swapped)? Do we need to reload the gdtr upon re-entering the kernel. After re-entering the kernel and returning from machine_kexec, restore_processor_state() is called, where the GDTR and some other CPU state such as FPU, IDT, etc are restored. > [..] > > @@ -197,8 +282,54 @@ identity_mapped: > > xorl %eax, %eax > > movl %eax, %cr3 > > > > + movl CP_PA_SWAP_PAGE(%edi), %eax > > + pushl %eax > > + pushl %ebx > > + call swap_pages > > + addl $8, %esp > > + > > + /* To be certain of avoiding problems with self-modifying code > > + * I need to execute a serializing instruction here. > > + * So I flush the TLB, it's handy, and not processor dependent. > > + */ > > + xorl %eax, %eax > > + movl %eax, %cr3 > > + > > + /* set all of the registers to known values */ > > + /* leave %esp alone */ > > + > > + movl KJUMP_MAGIC_OFF(%edi), %eax > > + cmpl $KJUMP_MAGIC_NUMBER, %eax > > + jz 1f > > + xorl %edi, %edi > > + xorl %eax, %eax > > + xorl %ebx, %ebx > > + xorl %ecx, %ecx > > + xorl %edx, %edx > > + xorl %esi, %esi > > + xorl %ebp, %ebp > > + ret > > +1: > > + popl %edx > > + movl CP_PA_SWAP_PAGE(%edi), %esp > > + addl $PAGE_SIZE_asm, %esp > > + pushl %edx > > +2: > > + call *%edx > > > + movl %edi, %edx > > + popl %edi > > + pushl %edx > > + jmp 2b > > + > > What does above piece of code do? Looks like redundant for switching > between the kernels? After call *%edx, we never return here. Instead > we come back to "kexec_jump_back_entry"? For switching between the kernels, this is redundant. Originally another feature of kexec jump is to call some code in physical mode. ?This is used to provide a C ABI to called code. Now, Eric suggests to use a C ABI compatible mode to pass the jump back entry point too, that is, use the return address on stack instead of % edi. I think that is reasonable. Maybe we can revise this code to be compatible with C ABI and provide a convenient interface for both kernel and other physical mode code. > [..] > > --- /dev/null > > +++ b/Documentation/i386/jump_back_protocol.txt > > @@ -0,0 +1,66 @@ > > + THE LINUX/I386 JUMP BACK PROTOCOL > > + --------------------------------- > > + > > + Huang Ying <ying.huang at intel.com> > > + Last update 2007-12-19 > > + > > +Currently, the following versions of the jump back protocol exist. > > + > > +Protocol 1.00: Jumping between original kernel and kexeced kernel > > + support. Calling ordinary C function support. > > + > > + > > +*** JUMP BACK ENTRY > > + > > +At jump back entry of callee, the CPU must be in 32-bit protected mode > > +with paging disabled; the CS, DS, ES and SS must be 4G flat segments; > > +CS must have execute/read permission, and DS, ES and SS must have > > +read/write permission; interrupt must be disabled; the contents of > > +registers and corresponding memory must be as follow: > > + > > +Offset/Size Meaning > > + > > +%edi Real jump back entry of caller if supported, > > + otherwise 0. > > +%esp Stack top pointer, the size of stack is about 4k bytes. > > +(%esp)/4 Helper jump back entry of caller if %edi != 0, > > + otherwise undefined. > > + > > I am not sure what is helper jump back entry? I understand that you > are using %edi to pass around entry point between two kernels. Can > you please shed some more light on this? Helper jump back entry is used to provide a C ABI to some physical mode code other than kernel. It is the above redundant code. Best Regards, Huang Ying
