From 6d7a5d1ea34495ecb1d608f0e40afba7776ee408 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Fri, 22 Jul 2011 14:39:49 +0930
Subject: lguest: don't rewrite vmcall instructions

Now we no longer use vmcall, we don't need to rewrite it in the Guest.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 drivers/lguest/x86/core.c | 77 -----------------------------------------------
 1 file changed, 77 deletions(-)

(limited to 'drivers/lguest/x86')

diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index 9f1659c3d1f..ec0cdfc04e7 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -352,69 +352,6 @@ static int emulate_insn(struct lg_cpu *cpu)
 	return 1;
 }
 
-/*
- * Our hypercalls mechanism used to be based on direct software interrupts.
- * After Anthony's "Refactor hypercall infrastructure" kvm patch, we decided to
- * change over to using kvm hypercalls.
- *
- * KVM_HYPERCALL is actually a "vmcall" instruction, which generates an invalid
- * opcode fault (fault 6) on non-VT cpus, so the easiest solution seemed to be
- * an *emulation approach*: if the fault was really produced by an hypercall
- * (is_hypercall() does exactly this check), we can just call the corresponding
- * hypercall host implementation function.
- *
- * But these invalid opcode faults are notably slower than software interrupts.
- * So we implemented the *patching (or rewriting) approach*: every time we hit
- * the KVM_HYPERCALL opcode in Guest code, we patch it to the old "int 0x1f"
- * opcode, so next time the Guest calls this hypercall it will use the
- * faster trap mechanism.
- *
- * Matias even benchmarked it to convince you: this shows the average cycle
- * cost of a hypercall.  For each alternative solution mentioned above we've
- * made 5 runs of the benchmark:
- *
- * 1) direct software interrupt: 2915, 2789, 2764, 2721, 2898
- * 2) emulation technique: 3410, 3681, 3466, 3392, 3780
- * 3) patching (rewrite) technique: 2977, 2975, 2891, 2637, 2884
- *
- * One two-line function is worth a 20% hypercall speed boost!
- */
-static void rewrite_hypercall(struct lg_cpu *cpu)
-{
-	/*
-	 * This are the opcodes we use to patch the Guest.  The opcode for "int
-	 * $0x1f" is "0xcd 0x1f" but vmcall instruction is 3 bytes long, so we
-	 * complete the sequence with a NOP (0x90).
-	 */
-	u8 insn[3] = {0xcd, 0x1f, 0x90};
-
-	__lgwrite(cpu, guest_pa(cpu, cpu->regs->eip), insn, sizeof(insn));
-	/*
-	 * The above write might have caused a copy of that page to be made
-	 * (if it was read-only).  We need to make sure the Guest has
-	 * up-to-date pagetables.  As this doesn't happen often, we can just
-	 * drop them all.
-	 */
-	guest_pagetable_clear_all(cpu);
-}
-
-static bool is_hypercall(struct lg_cpu *cpu)
-{
-	u8 insn[3];
-
-	/*
-	 * This must be the Guest kernel trying to do something.
-	 * The bottom two bits of the CS segment register are the privilege
-	 * level.
-	 */
-	if ((cpu->regs->cs & 3) != GUEST_PL)
-		return false;
-
-	/* Is it a vmcall? */
-	__lgread(cpu, insn, guest_pa(cpu, cpu->regs->eip), sizeof(insn));
-	return insn[0] == 0x0f && insn[1] == 0x01 && insn[2] == 0xc1;
-}
-
 /*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */
 void lguest_arch_handle_trap(struct lg_cpu *cpu)
 {
@@ -429,20 +366,6 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu)
 			if (emulate_insn(cpu))
 				return;
 		}
-		/*
-		 * If KVM is active, the vmcall instruction triggers a General
-		 * Protection Fault.  Normally it triggers an invalid opcode
-		 * fault (6):
-		 */
-	case 6:
-		/*
-		 * We need to check if ring == GUEST_PL and faulting
-		 * instruction == vmcall.
-		 */
-		if (is_hypercall(cpu)) {
-			rewrite_hypercall(cpu);
-			return;
-		}
 		break;
 	case 14: /* We've intercepted a Page Fault. */
 		/*
-- 
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