Linux Virtualization - Apr 2007 - [PATCH] Update lguest's patch code for new paravirt patch architecture

The new patching code means that we don't actually have to do as much
work in lguest's patcher.

We use paravirt_patch_default() for cases we don't want to patch
inline, which automatically handles the "patch iret to use a direct
jump" case.

There's no measurable effect on lguest's virtbench scores tho.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 drivers/lguest/lguest.c     |   10 ++--------
 drivers/lguest/lguest_asm.S |    1 -
 2 files changed, 2 insertions(+), 9 deletions(-)

==================================================================---
a/drivers/lguest/lguest.c
+++ b/drivers/lguest/lguest.c
@@ -388,7 +388,6 @@ static const struct lguest_insns
 	[PARAVIRT_PATCH(irq_enable)] = { lgstart_sti, lgend_sti },
 	[PARAVIRT_PATCH(restore_fl)] = { lgstart_popf, lgend_popf },
 	[PARAVIRT_PATCH(save_fl)] = { lgstart_pushf, lgend_pushf },
-	[PARAVIRT_PATCH(iret)] = { lgstart_iret, lgend_iret },
 };
 static unsigned lguest_patch(u8 type, u16 clobber, void *insns, unsigned len)
 {
@@ -396,20 +395,15 @@ static unsigned lguest_patch(u8 type, u1
 
 	/* Don't touch it if we don't have a replacement */
 	if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start)
-		return len;
+		return paravirt_patch_default(type, clobber, insns, len);
 
 	insn_len = lguest_insns[type].end - lguest_insns[type].start;
 
 	/* Similarly if we can't fit replacement. */
 	if (len < insn_len)
-		return len;
+		return paravirt_patch_default(type, clobber, insns, len);
 
 	memcpy(insns, lguest_insns[type].start, insn_len);
-	if (type == PARAVIRT_PATCH(iret)) {
-		/* Jumps are relative. */
-		u32 off = (u32)lguest_iret - ((u32)insns + insn_len);
-		memcpy(insns+1, &off, sizeof(off));
-	}
 	return insn_len;
 }
 
==================================================================---
a/drivers/lguest/lguest_asm.S
+++ b/drivers/lguest/lguest_asm.S
@@ -34,7 +34,6 @@ LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, l
 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)
-LGUEST_PATCH(iret, .byte 0xE9,0,0,0,0) /* jmp <to-be-patched> */
 
 .text
 /* These demark the EIP range where host should never deliver interrupts. */