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authorRusty Russell <rusty@rustcorp.com.au>2010-04-14 21:43:53 -0600
committerRusty Russell <rusty@rustcorp.com.au>2010-04-14 21:43:54 +0930
commit5094aeafbbd500509f648e3cd102b053bc7926b3 (patch)
tree8effa3dcde7c1b34ced9f09c7964acbcd8eb49f1 /drivers/lguest/x86
parent2ba3abd8186f24c7fb418927025b4e2120e3a362 (diff)
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 <rusty@rustcorp.com.au> Cc: Jeremy Fitzhardinge <jeremy@xensource.com> Cc: virtualization@lists.osdl.org
Diffstat (limited to 'drivers/lguest/x86')
-rw-r--r--drivers/lguest/x86/core.c12
1 files changed, 12 insertions, 0 deletions
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
@@ -288,6 +288,18 @@ static int emulate_insn(struct lg_cpu *cpu)
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.
*/