lguest: use KVM hypercalls

Impact: cleanup

This patch allow us to use KVM hypercalls

Signed-off-by: Matias Zabaljauregui <zabaljauregui at gmail.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

6 files changed, 122 insertions, 57 deletions

diff --git a/arch/x86/include/asm/lguest_hcall.h b/arch/x86/include/asm/lguest_hcall.h
index 43894428c3c2..0f4ee7148afe 100644
--- a/arch/x86/include/asm/lguest_hcall.h
+++ b/arch/x86/include/asm/lguest_hcall.h
@@ -26,36 +26,20 @@
 
 #ifndef __ASSEMBLY__
 #include <asm/hw_irq.h>
+#include <asm/kvm_para.h>
 
 /*G:031 But first, how does our Guest contact the Host to ask for privileged
  * operations?  There are two ways: the direct way is to make a "hypercall",
  * to make requests of the Host Itself.
  *
- * Our hypercall mechanism uses the highest unused trap code (traps 32 and
- * above are used by real hardware interrupts).  Fifteen hypercalls are
+ * We use the KVM hypercall mechanism. Eighteen hypercalls are
  * available: the hypercall number is put in the %eax register, and the
- * arguments (when required) are placed in %edx, %ebx and %ecx.  If a return
+ * arguments (when required) are placed in %ebx, %ecx and %edx.  If a return
  * value makes sense, it's returned in %eax.
  *
  * Grossly invalid calls result in Sudden Death at the hands of the vengeful
  * Host, rather than returning failure.  This reflects Winston Churchill's
  * definition of a gentleman: "someone who is only rude intentionally". */
-static inline unsigned long
-hcall(unsigned long call,
-      unsigned long arg1, unsigned long arg2, unsigned long arg3)
-{
-        /* "int" is the Intel instruction to trigger a trap. */
-        asm volatile("int $" __stringify(LGUEST_TRAP_ENTRY)
-                     /* The call in %eax (aka "a") might be overwritten */
-                     : "=a"(call)
-                       /* The arguments are in %eax, %edx, %ebx & %ecx */
-                     : "a"(call), "d"(arg1), "b"(arg2), "c"(arg3)
-                       /* "memory" means this might write somewhere in memory.
-                        * This isn't true for all calls, but it's safe to tell
-                        * gcc that it might happen so it doesn't get clever. */
-                     : "memory");
-        return call;
-}
 /*:*/
 
 /* Can't use our min() macro here: needs to be a constant */
@@ -64,7 +48,7 @@ hcall(unsigned long call,
 #define LHCALL_RING_SIZE 64
 struct hcall_args {
         /* These map directly onto eax, ebx, ecx, edx in struct lguest_regs */
-        unsigned long arg0, arg2, arg3, arg1;
+        unsigned long arg0, arg1, arg2, arg3;
 };
 
 #endif /* !__ASSEMBLY__ */
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 7822d29b02c7..5be9293961ba 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -107,7 +107,7 @@ static void async_hcall(unsigned long call, unsigned long arg1,
         local_irq_save(flags);
         if (lguest_data.hcall_status[next_call] != 0xFF) {
                 /* Table full, so do normal hcall which will flush table. */
-                hcall(call, arg1, arg2, arg3);
+                kvm_hypercall3(call, arg1, arg2, arg3);
         } else {
                 lguest_data.hcalls[next_call].arg0 = call;
                 lguest_data.hcalls[next_call].arg1 = arg1;
@@ -134,13 +134,32 @@ static void async_hcall(unsigned long call, unsigned long arg1,
  *
  * So, when we're in lazy mode, we call async_hcall() to store the call for
  * future processing: */
-static void lazy_hcall(unsigned long call,
+static void lazy_hcall1(unsigned long call,
+                       unsigned long arg1)
+{
+        if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
+                kvm_hypercall1(call, arg1);
+        else
+                async_hcall(call, arg1, 0, 0);
+}
+
+static void lazy_hcall2(unsigned long call,
+                       unsigned long arg1,
+                       unsigned long arg2)
+{
+        if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
+                kvm_hypercall2(call, arg1, arg2);
+        else
+                async_hcall(call, arg1, arg2, 0);
+}
+
+static void lazy_hcall3(unsigned long call,
                        unsigned long arg1,
                        unsigned long arg2,
                        unsigned long arg3)
 {
         if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
-                hcall(call, arg1, arg2, arg3);
+                kvm_hypercall3(call, arg1, arg2, arg3);
         else
                 async_hcall(call, arg1, arg2, arg3);
 }
@@ -150,7 +169,7 @@ static void lazy_hcall(unsigned long call,
 static void lguest_leave_lazy_mode(void)
 {
         paravirt_leave_lazy(paravirt_get_lazy_mode());
-        hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
+        kvm_hypercall0(LHCALL_FLUSH_ASYNC);
 }
 
 /*G:033
@@ -229,7 +248,7 @@ static void lguest_write_idt_entry(gate_desc *dt,
         /* Keep the local copy up to date. */
         native_write_idt_entry(dt, entrynum, g);
         /* Tell Host about this new entry. */
-        hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, desc[0], desc[1]);
+        kvm_hypercall3(LHCALL_LOAD_IDT_ENTRY, entrynum, desc[0], desc[1]);
 }
 
 /* Changing to a different IDT is very rare: we keep the IDT up-to-date every
@@ -241,7 +260,7 @@ static void lguest_load_idt(const struct desc_ptr *desc)
         struct desc_struct *idt = (void *)desc->address;
 
         for (i = 0; i < (desc->size+1)/8; i++)
-                hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
+                kvm_hypercall3(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
 }
 
 /*
@@ -261,8 +280,8 @@ static void lguest_load_idt(const struct desc_ptr *desc)
  */
 static void lguest_load_gdt(const struct desc_ptr *desc)
 {
-        BUG_ON((desc->size+1)/8 != GDT_ENTRIES);
-        hcall(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES, 0);
+        BUG_ON((desc->size + 1) / 8 != GDT_ENTRIES);
+        kvm_hypercall2(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES);
 }
 
 /* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
@@ -272,7 +291,7 @@ static void lguest_write_gdt_entry(struct desc_struct *dt, int entrynum,
                                    const void *desc, int type)
 {
         native_write_gdt_entry(dt, entrynum, desc, type);
-        hcall(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES, 0);
+        kvm_hypercall2(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES);
 }
 
 /* OK, I lied.  There are three "thread local storage" GDT entries which change
@@ -284,7 +303,7 @@ static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
          * can't handle us removing entries we're currently using.  So we clear
          * the GS register here: if it's needed it'll be reloaded anyway. */
         lazy_load_gs(0);
-        lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
+        lazy_hcall2(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu);
 }
 
 /*G:038 That's enough excitement for now, back to ploughing through each of
@@ -382,7 +401,7 @@ static void lguest_cpuid(unsigned int *ax, unsigned int *bx,
 static unsigned long current_cr0;
 static void lguest_write_cr0(unsigned long val)
 {
-        lazy_hcall(LHCALL_TS, val & X86_CR0_TS, 0, 0);
+        lazy_hcall1(LHCALL_TS, val & X86_CR0_TS);
         current_cr0 = val;
 }
 
@@ -396,7 +415,7 @@ static unsigned long lguest_read_cr0(void)
  * the vowels have been optimized out. */
 static void lguest_clts(void)
 {
-        lazy_hcall(LHCALL_TS, 0, 0, 0);
+        lazy_hcall1(LHCALL_TS, 0);
         current_cr0 &= ~X86_CR0_TS;
 }
 
@@ -418,7 +437,7 @@ static bool cr3_changed = false;
 static void lguest_write_cr3(unsigned long cr3)
 {
         lguest_data.pgdir = cr3;
-        lazy_hcall(LHCALL_NEW_PGTABLE, cr3, 0, 0);
+        lazy_hcall1(LHCALL_NEW_PGTABLE, cr3);
         cr3_changed = true;
 }
 
@@ -493,7 +512,7 @@ static void lguest_write_cr4(unsigned long val)
 static void lguest_pte_update(struct mm_struct *mm, unsigned long addr,
                                pte_t *ptep)
 {
-        lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, ptep->pte_low);
+        lazy_hcall3(LHCALL_SET_PTE, __pa(mm->pgd), addr, ptep->pte_low);
 }
 
 static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
@@ -509,8 +528,8 @@ static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
 static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
 {
         *pmdp = pmdval;
-        lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK,
-                   (__pa(pmdp)&(PAGE_SIZE-1))/4, 0);
+        lazy_hcall2(LHCALL_SET_PMD, __pa(pmdp) & PAGE_MASK,
+                   (__pa(pmdp) & (PAGE_SIZE - 1)) / 4);
 }
 
 /* There are a couple of legacy places where the kernel sets a PTE, but we
@@ -526,7 +545,7 @@ static void lguest_set_pte(pte_t *ptep, pte_t pteval)
 {
         *ptep = pteval;
         if (cr3_changed)
-                lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
+                lazy_hcall1(LHCALL_FLUSH_TLB, 1);
 }
 
 /* Unfortunately for Lguest, the pv_mmu_ops for page tables were based on
@@ -542,7 +561,7 @@ static void lguest_set_pte(pte_t *ptep, pte_t pteval)
 static void lguest_flush_tlb_single(unsigned long addr)
 {
         /* Simply set it to zero: if it was not, it will fault back in. */
-        lazy_hcall(LHCALL_SET_PTE, lguest_data.pgdir, addr, 0);
+        lazy_hcall3(LHCALL_SET_PTE, lguest_data.pgdir, addr, 0);
 }
 
 /* This is what happens after the Guest has removed a large number of entries.
@@ -550,7 +569,7 @@ static void lguest_flush_tlb_single(unsigned long addr)
  * have changed, ie. virtual addresses below PAGE_OFFSET. */
 static void lguest_flush_tlb_user(void)
 {
-        lazy_hcall(LHCALL_FLUSH_TLB, 0, 0, 0);
+        lazy_hcall1(LHCALL_FLUSH_TLB, 0);
 }
 
 /* This is called when the kernel page tables have changed.  That's not very
@@ -558,7 +577,7 @@ static void lguest_flush_tlb_user(void)
  * slow), so it's worth separating this from the user flushing above. */
 static void lguest_flush_tlb_kernel(void)
 {
-        lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
+        lazy_hcall1(LHCALL_FLUSH_TLB, 1);
 }
 
 /*
@@ -695,7 +714,7 @@ static int lguest_clockevent_set_next_event(unsigned long delta,
         }
 
         /* Please wake us this far in the future. */
-        hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0);
+        kvm_hypercall1(LHCALL_SET_CLOCKEVENT, delta);
         return 0;
 }
 
@@ -706,7 +725,7 @@ static void lguest_clockevent_set_mode(enum clock_event_mode mode,
         case CLOCK_EVT_MODE_UNUSED:
         case CLOCK_EVT_MODE_SHUTDOWN:
                 /* A 0 argument shuts the clock down. */
-                hcall(LHCALL_SET_CLOCKEVENT, 0, 0, 0);
+                kvm_hypercall0(LHCALL_SET_CLOCKEVENT);
                 break;
         case CLOCK_EVT_MODE_ONESHOT:
                 /* This is what we expect. */
@@ -781,8 +800,8 @@ static void lguest_time_init(void)
 static void lguest_load_sp0(struct tss_struct *tss,
                             struct thread_struct *thread)
 {
-        lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->sp0,
-                   THREAD_SIZE/PAGE_SIZE);
+        lazy_hcall3(LHCALL_SET_STACK, __KERNEL_DS | 0x1, thread->sp0,
+                   THREAD_SIZE / PAGE_SIZE);
 }
 
 /* Let's just say, I wouldn't do debugging under a Guest. */
@@ -855,7 +874,7 @@ static void set_lguest_basic_apic_ops(void)
 /* STOP!  Until an interrupt comes in. */
 static void lguest_safe_halt(void)
 {
-        hcall(LHCALL_HALT, 0, 0, 0);
+        kvm_hypercall0(LHCALL_HALT);
 }
 
 /* The SHUTDOWN hypercall takes a string to describe what's happening, and
@@ -865,7 +884,8 @@ static void lguest_safe_halt(void)
  * rather than virtual addresses, so we use __pa() here. */
 static void lguest_power_off(void)
 {
-        hcall(LHCALL_SHUTDOWN, __pa("Power down"), LGUEST_SHUTDOWN_POWEROFF, 0);
+        kvm_hypercall2(LHCALL_SHUTDOWN, __pa("Power down"),
+                                        LGUEST_SHUTDOWN_POWEROFF);
 }
 
 /*
@@ -875,7 +895,7 @@ static void lguest_power_off(void)
  */
 static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p)
 {
-        hcall(LHCALL_SHUTDOWN, __pa(p), LGUEST_SHUTDOWN_POWEROFF, 0);
+        kvm_hypercall2(LHCALL_SHUTDOWN, __pa(p), LGUEST_SHUTDOWN_POWEROFF);
         /* The hcall won't return, but to keep gcc happy, we're "done". */
         return NOTIFY_DONE;
 }
@@ -916,7 +936,7 @@ static __init int early_put_chars(u32 vtermno, const char *buf, int count)
                 len = sizeof(scratch) - 1;
         scratch[len] = '\0';
         memcpy(scratch, buf, len);
-        hcall(LHCALL_NOTIFY, __pa(scratch), 0, 0);
+        kvm_hypercall1(LHCALL_NOTIFY, __pa(scratch));
 
         /* This routine returns the number of bytes actually written. */
         return len;
@@ -926,7 +946,7 @@ static __init int early_put_chars(u32 vtermno, const char *buf, int count)
  * Launcher to reboot us. */
 static void lguest_restart(char *reason)
 {
-        hcall(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART, 0);
+        kvm_hypercall2(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART);
 }
 
 /*G:050
diff --git a/arch/x86/lguest/i386_head.S b/arch/x86/lguest/i386_head.S
index 10b9bd35a8ff..f79541989471 100644
--- a/arch/x86/lguest/i386_head.S
+++ b/arch/x86/lguest/i386_head.S
@@ -27,8 +27,8 @@ ENTRY(lguest_entry)
         /* We make the "initialization" hypercall now to tell the Host about
          * us, and also find out where it put our page tables. */
         movl $LHCALL_LGUEST_INIT, %eax
-        movl $lguest_data - __PAGE_OFFSET, %edx
-        int $LGUEST_TRAP_ENTRY
+        movl $lguest_data - __PAGE_OFFSET, %ebx
+        .byte 0x0f,0x01,0xc1 /* KVM_HYPERCALL */
 
         /* Set up the initial stack so we can run C code. */
         movl $(init_thread_union+THREAD_SIZE),%esp
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. */