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>

2 files changed, 2 insertions, 81 deletions

diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index daaf86631647..f0c171506371 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -375,11 +375,9 @@ static bool direct_trap(unsigned int num)
         /*
          * The Host needs to see page faults (for shadow paging and to save the
          * fault address), general protection faults (in/out emulation) and
-         * device not available (TS handling), invalid opcode fault (kvm hcall),
-         * and of course, the hypercall trap.
+         * device not available (TS handling) and of course, the hypercall trap.
          */
-        return num != 14 && num != 13 && num != 7 &&
-                        num != 6 && num != LGUEST_TRAP_ENTRY;
+        return num != 14 && num != 13 && num != 7 && num != LGUEST_TRAP_ENTRY;
 }
 /*:*/
 
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index 9f1659c3d1f3..ec0cdfc04e78 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. */
                 /*