lguest: the guest code
lguest is a simple hypervisor for Linux on Linux. Unlike kvm it doesn't need
VT/SVM hardware. Unlike Xen it's simply "modprobe and go". Unlike both, it's
5000 lines and self-contained.
Performance is ok, but not great (-30% on kernel compile). But given its
hackability, I expect this to improve, along with the paravirt_ops code which
it supplies a complete example for. There's also a 64-bit version being
worked on and other craziness.
But most of all, lguest is awesome fun! Too much of the kernel is a big ball
of hair. lguest is simple enough to dive into and hack, plus has some warts
which scream "fork me!".
This patch:
This is the code and headers required to make an i386 kernel an lguest guest.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andi Kleen <ak@suse.de>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/lguest/lguest_asm.S b/drivers/lguest/lguest_asm.S
new file mode 100644
index 0000000..5ac3d20
--- /dev/null
+++ b/drivers/lguest/lguest_asm.S
@@ -0,0 +1,53 @@
+#include <linux/linkage.h>
+#include <linux/lguest.h>
+#include <asm/asm-offsets.h>
+#include <asm/thread_info.h>
+
+/* FIXME: Once asm/processor-flags.h goes in, include that */
+#define X86_EFLAGS_IF 0x00000200
+
+/*
+ * This is where we begin: we have a magic signature which the launcher looks
+ * for. The plan is that the Linux boot protocol will be extended with a
+ * "platform type" field which will guide us here from the normal entry point,
+ * but for the moment this suffices.
+ *
+ * We put it in .init.text will be discarded after boot.
+ */
+.section .init.text, "ax", @progbits
+.ascii "GenuineLguest"
+ /* Set up initial stack. */
+ movl $(init_thread_union+THREAD_SIZE),%esp
+ jmp lguest_init
+
+/* The templates for inline patching. */
+#define LGUEST_PATCH(name, insns...) \
+ lgstart_##name: insns; lgend_##name:; \
+ .globl lgstart_##name; .globl lgend_##name
+
+LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
+LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled)
+LGUEST_PATCH(popf, movl %eax, lguest_data+LGUEST_DATA_irq_enabled)
+LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
+
+.text
+/* These demark the EIP range where host should never deliver interrupts. */
+.global lguest_noirq_start
+.global lguest_noirq_end
+
+/*
+ * We move eflags word to lguest_data.irq_enabled to restore interrupt state.
+ * For page faults, gpfs and virtual interrupts, the hypervisor has saved
+ * eflags manually, otherwise it was delivered directly and so eflags reflects
+ * the real machine IF state, ie. interrupts on. Since the kernel always dies
+ * if it takes such a trap with interrupts disabled anyway, turning interrupts
+ * back on unconditionally here is OK.
+ */
+ENTRY(lguest_iret)
+ pushl %eax
+ movl 12(%esp), %eax
+lguest_noirq_start:
+ movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled
+ popl %eax
+ iret
+lguest_noirq_end: