diff options
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/lguest/interrupts_and_traps.c | 7 | ||||
| -rw-r--r-- | drivers/lguest/lguest_device.c | 4 | ||||
| -rw-r--r-- | drivers/lguest/x86/core.c | 62 |
3 files changed, 67 insertions, 6 deletions
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c index 415fab0125ac..504091da1737 100644 --- a/drivers/lguest/interrupts_and_traps.c +++ b/drivers/lguest/interrupts_and_traps.c @@ -288,9 +288,10 @@ static int 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), and of course, the hypercall - * trap. */ - return num != 14 && num != 13 && num != 7 && num != LGUEST_TRAP_ENTRY; + * device not available (TS handling), invalid opcode fault (kvm hcall), + * and of course, the hypercall trap. */ + return num != 14 && num != 13 && num != 7 && + num != 6 && num != LGUEST_TRAP_ENTRY; } /*:*/ diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c index 8132533d71f9..df44d962626d 100644 --- a/drivers/lguest/lguest_device.c +++ b/drivers/lguest/lguest_device.c @@ -161,7 +161,7 @@ static void set_status(struct virtio_device *vdev, u8 status) /* We set the status. */ to_lgdev(vdev)->desc->status = status; - hcall(LHCALL_NOTIFY, (max_pfn<<PAGE_SHIFT) + offset, 0, 0); + kvm_hypercall1(LHCALL_NOTIFY, (max_pfn << PAGE_SHIFT) + offset); } static void lg_set_status(struct virtio_device *vdev, u8 status) @@ -209,7 +209,7 @@ static void lg_notify(struct virtqueue *vq) * virtqueue structure. */ struct lguest_vq_info *lvq = vq->priv; - hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0); + kvm_hypercall1(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT); } /* An extern declaration inside a C file is bad form. Don't do it. */ diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c index bf7942327bda..a6b717644be0 100644 --- a/drivers/lguest/x86/core.c +++ b/drivers/lguest/x86/core.c @@ -290,6 +290,57 @@ 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)); +} + +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) { @@ -337,7 +388,7 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu) break; case 32 ... 255: /* These values mean a real interrupt occurred, in which case - * the Host handler has already been run. We just do a + * the Host handler has already been run. We just do a * friendly check if another process should now be run, then * return to run the Guest again */ cond_resched(); @@ -347,6 +398,15 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu) * up the pointer now to indicate a hypercall is pending. */ cpu->hcall = (struct hcall_args *)cpu->regs; return; + case 6: + /* kvm hypercalls trigger an invalid opcode fault (6). + * We need to check if ring == GUEST_PL and + * faulting instruction == vmcall. */ + if (is_hypercall(cpu)) { + rewrite_hypercall(cpu); + return; + } + break; } /* We didn't handle the trap, so it needs to go to the Guest. */ |