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 CPUstate 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 anotherfeature of kexec jump is to call some code in physical mode. This isused to provide a C ABI to called code. Now, Eric suggests to use a C ABI compatible mode to pass the jump backentry 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 becompatible with C ABI and provide a convenient interface for both kerneland 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@xxxxxxxxx>> > + 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 modecode other than kernel. It is the above redundant code. Best Regards,Huang Ying _______________________________________________linux-pm mailing listlinux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx://lists.linux-foundation.org/mailman/listinfo/linux-pm
