Hacking on Lguest Rusty Russell IBM Linux Technology Center (OzLabs)

5 Minute Lguest Mastery Simplest virtualization possible Linux-on-linux 32-bit x86 only Code documented!

5 Minute Lguest Mastery Launcher loads/services Guest: –Documentation/lguest/lguest.c Guest kernel has lg support –drivers/lguest/lguest{,_asm,_bus}.c Host kernel has lg module –drivers/lguest/*.c

5 Minute Lguest Mastery Launcher: –Documentation/lguest/lguest.c –Writes to /dev/lguest: LHCALL_INITIALIZE LHCALL_IRQ LHCALL_GETDMA LHCALL_BREAK –Reads to run Guest –Handles devices, net/char input

5 Minute Lguest Mastery Guest: –drivers/lguest/lguest{,_asm,_bus}.c –Special lguest_net/block/console drivers –Makes "hypercalls" to Host: See include/linux/lguest.h unsigned long hcall(unsigned long call, unsigned long arg1, unsigned long arg2, unsigned long arg3)

5 Minute Lguest Mastery Host: –drivers/lguest/*.c –Switches to Guest, switched back in any interrupt or hypercall –Handles traps and hypercalls –Returns to Launcher on DMA out to "devices"

1 Minute Lguest Mastery Launcher Host /dev/lguest

1 Minute Lguest Mastery Launcher Host write():

1 Minute Lguest Mastery Launcher Host write(): LHREQ_INITIALIZE pages-of-memory address of top-level pagetable address to start executing PAGE_OFFSET for kernel

1 Minute Lguest Mastery Launcher Host read(): unsigned long dmainfo[2]

1 Minute Lguest Mastery Launcher Host read(): unsigned long dmainfo[2] -> EAGAIN (interrupted by waker) -> ENOENT (guest died) -> >0 (dma from guest)

1 Minute Lguest Mastery Launcher Host Guest

1 Minute Lguest Mastery Launcher Host Guest eax=LHCALL_LGUEST_INIT edx=address of lguest_data ebx=0 ecx=0

1 Minute Lguest Mastery Launcher Host Guest int 15 eax=LHCALL_LGUEST_INIT edx=address of lguest_data ebx=0 ecx=0

The Plan

Features

Features: Simple S-gname: Write a new hypercall which prints your name using printk(). S-lzzz: Implement a new control sequence ^Z^Z^Z

Features: Simple S-lnetst: Fix Launcher to warn if discarding packets when LGUEST_DEVICE_S_ACTIVE S-lstatus: Print out device status when 'status' comes in the control fd

Features: Simple S-greboothook: Reboot hook in Guest S-lshutdown: Launcher clean exit on Guest shutdown. S-lreboot: Have the Launcher "reboot" itself when the final read returns -ELOOP. S-lctrlzzz: Suspend when told to by the control fd

Features: Medium M-hiofix: Fix lguest I/O bug for shared pages M-lsuspend: Suspend Guest into memory file M-lrestore: Restore Guest from memory file

Features: Advanced A-lmatchmem: Print matching memory among Guests A-lsharemem: Share exported matching memory A-grtc: Implement /dev/rtc for the Guest

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