Merge tag 'virtio-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux

Pull virtio updates from Rusty Russell:
 "Some virtio internal cleanups, a new virtio device "virtio input", and
  a change to allow the legacy virtio balloon.

  Most excitingly, some lguest work! No seriously, I got some cleanup
  patches"

* tag 'virtio-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux:
  virtio: drop virtio_device_is_legacy_only
  virtio_pci: support non-legacy balloon devices
  virtio_mmio: support non-legacy balloon devices
  virtio_ccw: support non-legacy balloon devices
  virtio: balloon might not be a legacy device
  virtio_balloon: transitional interface
  virtio_ring: Update weak barriers to use dma_wmb/rmb
  virtio_pci_modern: switch to type-safe io accessors
  virtio_pci_modern: type-safe io accessors
  lguest: handle traps on the "interrupt suppressed" iret instruction.
  virtio: drop a useless config read
  virtio_config: reorder functions
  Add virtio-input driver.
  lguest: suppress interrupts for single insn, not range.
  lguest: simplify lguest_iret
  lguest: rename i386_head.S in the comments
  lguest: explicitly set miscdevice's private_data NULL
  lguest: fix pending interrupt test.

drivers/lguest/hypercalls.c

@@ -211,10 +211,9 @@ static void initialize(struct lg_cpu *cpu)
 
 	/*
 	 * The Guest tells us where we're not to deliver interrupts by putting
-	 * the range of addresses into "struct lguest_data".
+	 * the instruction address into "struct lguest_data".
 	 */
-	if (get_user(cpu->lg->noirq_start, &cpu->lg->lguest_data->noirq_start)
-	    || get_user(cpu->lg->noirq_end, &cpu->lg->lguest_data->noirq_end))
+	if (get_user(cpu->lg->noirq_iret, &cpu->lg->lguest_data->noirq_iret))
 		kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
 
 	/*

drivers/lguest/interrupts_and_traps.c

@@ -56,21 +56,16 @@ static void push_guest_stack(struct lg_cpu *cpu, unsigned long *gstack, u32 val)
 }
 
 /*H:210
- * The set_guest_interrupt() routine actually delivers the interrupt or
- * trap.  The mechanics of delivering traps and interrupts to the Guest are the
- * same, except some traps have an "error code" which gets pushed onto the
- * stack as well: the caller tells us if this is one.
- *
- * "lo" and "hi" are the two parts of the Interrupt Descriptor Table for this
- * interrupt or trap.  It's split into two parts for traditional reasons: gcc
- * on i386 used to be frightened by 64 bit numbers.
+ * The push_guest_interrupt_stack() routine saves Guest state on the stack for
+ * an interrupt or trap.  The mechanics of delivering traps and interrupts to
+ * the Guest are the same, except some traps have an "error code" which gets
+ * pushed onto the stack as well: the caller tells us if this is one.
  *
  * We set up the stack just like the CPU does for a real interrupt, so it's
  * identical for the Guest (and the standard "iret" instruction will undo
  * it).
  */
-static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
-				bool has_err)
+static void push_guest_interrupt_stack(struct lg_cpu *cpu, bool has_err)
 {
 	unsigned long gstack, origstack;
 	u32 eflags, ss, irq_enable;
@@ -130,12 +125,28 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
 	if (has_err)
 		push_guest_stack(cpu, &gstack, cpu->regs->errcode);
 
-	/*
-	 * Now we've pushed all the old state, we change the stack, the code
-	 * segment and the address to execute.
-	 */
+	/* Adjust the stack pointer and stack segment. */
 	cpu->regs->ss = ss;
 	cpu->regs->esp = virtstack + (gstack - origstack);
+}
+
+/*
+ * This actually makes the Guest start executing the given interrupt/trap
+ * handler.
+ *
+ * "lo" and "hi" are the two parts of the Interrupt Descriptor Table for this
+ * interrupt or trap.  It's split into two parts for traditional reasons: gcc
+ * on i386 used to be frightened by 64 bit numbers.
+ */
+static void guest_run_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi)
+{
+	/* If we're already in the kernel, we don't change stacks. */
+	if ((cpu->regs->ss&0x3) != GUEST_PL)
+		cpu->regs->ss = cpu->esp1;
+
+	/*
+	 * Set the code segment and the address to execute.
+	 */
 	cpu->regs->cs = (__KERNEL_CS|GUEST_PL);
 	cpu->regs->eip = idt_address(lo, hi);
 
@@ -158,6 +169,24 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
 			kill_guest(cpu, "Disabling interrupts");
 }
 
+/* This restores the eflags word which was pushed on the stack by a trap */
+static void restore_eflags(struct lg_cpu *cpu)
+{
+	/* This is the physical address of the stack. */
+	unsigned long stack_pa = guest_pa(cpu, cpu->regs->esp);
+
+	/*
+	 * Stack looks like this:
+	 * Address	Contents
+	 * esp		EIP
+	 * esp + 4	CS
+	 * esp + 8	EFLAGS
+	 */
+	cpu->regs->eflags = lgread(cpu, stack_pa + 8, u32);
+	cpu->regs->eflags &=
+		~(X86_EFLAGS_TF|X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT);
+}
+
 /*H:205
  * Virtual Interrupts.
  *
@@ -200,14 +229,6 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
 
 	BUG_ON(irq >= LGUEST_IRQS);
 
-	/*
-	 * They may be in the middle of an iret, where they asked us never to
-	 * deliver interrupts.
-	 */
-	if (cpu->regs->eip >= cpu->lg->noirq_start &&
-	   (cpu->regs->eip < cpu->lg->noirq_end))
-		return;
-
 	/* If they're halted, interrupts restart them. */
 	if (cpu->halted) {
 		/* Re-enable interrupts. */
@@ -237,12 +258,34 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
 	if (idt_present(idt->a, idt->b)) {
 		/* OK, mark it no longer pending and deliver it. */
 		clear_bit(irq, cpu->irqs_pending);
+
 		/*
-		 * set_guest_interrupt() takes the interrupt descriptor and a
-		 * flag to say whether this interrupt pushes an error code onto
-		 * the stack as well: virtual interrupts never do.
+		 * They may be about to iret, where they asked us never to
+		 * deliver interrupts.  In this case, we can emulate that iret
+		 * then immediately deliver the interrupt.  This is basically
+		 * a noop: the iret would pop the interrupt frame and restore
+		 * eflags, and then we'd set it up again.  So just restore the
+		 * eflags word and jump straight to the handler in this case.
+		 *
+		 * Denys Vlasenko points out that this isn't quite right: if
+		 * the iret was returning to userspace, then that interrupt
+		 * would reset the stack pointer (which the Guest told us
+		 * about via LHCALL_SET_STACK).  But unless the Guest is being
+		 * *really* weird, that will be the same as the current stack
+		 * anyway.
 		 */
-		set_guest_interrupt(cpu, idt->a, idt->b, false);
+		if (cpu->regs->eip == cpu->lg->noirq_iret) {
+			restore_eflags(cpu);
+		} else {
+			/*
+			 * set_guest_interrupt() takes a flag to say whether
+			 * this interrupt pushes an error code onto the stack
+			 * as well: virtual interrupts never do.
+			 */
+			push_guest_interrupt_stack(cpu, false);
+		}
+		/* Actually make Guest cpu jump to handler. */
+		guest_run_interrupt(cpu, idt->a, idt->b);
 	}
 
 	/*
@@ -353,8 +396,9 @@ bool deliver_trap(struct lg_cpu *cpu, unsigned int num)
 	 */
 	if (!idt_present(cpu->arch.idt[num].a, cpu->arch.idt[num].b))
 		return false;
-	set_guest_interrupt(cpu, cpu->arch.idt[num].a,
-			    cpu->arch.idt[num].b, has_err(num));
+	push_guest_interrupt_stack(cpu, has_err(num));
+	guest_run_interrupt(cpu, cpu->arch.idt[num].a,
+			    cpu->arch.idt[num].b);
 	return true;
 }
 
@@ -395,8 +439,9 @@ static bool direct_trap(unsigned int num)
  * The Guest has the ability to turn its interrupt gates into trap gates,
  * if it is careful.  The Host will let trap gates can go directly to the
  * Guest, but the Guest needs the interrupts atomically disabled for an
- * interrupt gate.  It can do this by pointing the trap gate at instructions
- * within noirq_start and noirq_end, where it can safely disable interrupts.
+ * interrupt gate.  The Host could provide a mechanism to register more
+ * "no-interrupt" regions, and the Guest could point the trap gate at
+ * instructions within that region, where it can safely disable interrupts.
  */
 
 /*M:006

drivers/lguest/lg.h

@@ -102,7 +102,7 @@ struct lguest {
 
 	struct pgdir pgdirs[4];
 
-	unsigned long noirq_start, noirq_end;
+	unsigned long noirq_iret;
 
 	unsigned int stack_pages;
 	u32 tsc_khz;

drivers/lguest/lguest_user.c

@@ -339,6 +339,13 @@ static ssize_t write(struct file *file, const char __user *in,
 	}
 }
 
+static int open(struct inode *inode, struct file *file)
+{
+	file->private_data = NULL;
+
+	return 0;
+}
+
 /*L:060
  * The final piece of interface code is the close() routine.  It reverses
  * everything done in initialize().  This is usually called because the
@@ -409,6 +416,7 @@ static int close(struct inode *inode, struct file *file)
  */
 static const struct file_operations lguest_fops = {
 	.owner	 = THIS_MODULE,
+	.open	 = open,
 	.release = close,
 	.write	 = write,
 	.read	 = read,