From 5094aeafbbd500509f648e3cd102b053bc7926b3 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Wed, 14 Apr 2010 21:43:53 -0600 Subject: [PATCH] lguest: workaround cmpxchg8b_emu by ignoring cli in the guest. It's only used by cmpxchg8b_emu (see db677ffa5f5a for the gory details), and fixing that to be paravirt aware would be more work than simply ignoring it (and AFAICT only help lguest). This makes lguest work on machines which have cmpxchg8b, for kernels compiled for older processors. (We can't emulate it properly: the popf which expects to restore interrupts does not trap). Signed-off-by: Rusty Russell Cc: Jeremy Fitzhardinge Cc: virtualization@lists.osdl.org --- drivers/lguest/x86/core.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c index fb2b7ef7868e..b4eb675a807e 100644 --- a/drivers/lguest/x86/core.c +++ b/drivers/lguest/x86/core.c @@ -287,6 +287,18 @@ static int emulate_insn(struct lg_cpu *cpu) /* Decoding x86 instructions is icky. */ insn = lgread(cpu, physaddr, u8); + /* + * Around 2.6.33, the kernel started using an emulation for the + * cmpxchg8b instruction in early boot on many configurations. This + * code isn't paravirtualized, and it tries to disable interrupts. + * Ignore it, which will Mostly Work. + */ + if (insn == 0xfa) { + /* "cli", or Clear Interrupt Enable instruction. Skip it. */ + cpu->regs->eip++; + return 1; + } + /* * 0x66 is an "operand prefix". It means it's using the upper 16 bits * of the eax register. -- 2.20.1