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authorRusty Russell <rusty@rustcorp.com.au>2011-07-22 14:39:49 +0930
committerRusty Russell <rusty@rustcorp.com.au>2011-07-22 14:39:49 +0930
commit6d7a5d1ea34495ecb1d608f0e40afba7776ee408 (patch)
tree23213877e952ad122888a502d07ed112263069d6 /drivers/lguest
parent7e1941444f808d8001aa3b63588150c516321a3c (diff)
downloadlwn-6d7a5d1ea34495ecb1d608f0e40afba7776ee408.tar.gz
lwn-6d7a5d1ea34495ecb1d608f0e40afba7776ee408.zip
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>
Diffstat (limited to 'drivers/lguest')
-rw-r--r--drivers/lguest/interrupts_and_traps.c6
-rw-r--r--drivers/lguest/x86/core.c77
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. */
/*