lguest: add iomem region, where guest page faults get sent to userspace.

This lets us implement PCI.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/lguest/lg.h

@@ -97,8 +97,12 @@ struct lguest {
 	struct lg_cpu cpus[NR_CPUS];
 	unsigned int nr_cpus;
 
+	/* Valid guest memory pages must be < this. */
 	u32 pfn_limit;
 
+	/* Device memory is >= pfn_limit and < device_limit. */
+	u32 device_limit;
+
 	/*
 	 * This provides the offset to the base of guest-physical memory in the
 	 * Launcher.
@@ -200,7 +204,8 @@ void guest_pagetable_flush_user(struct lg_cpu *cpu);
 void guest_set_pte(struct lg_cpu *cpu, unsigned long gpgdir,
 		   unsigned long vaddr, pte_t val);
 void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages);
-bool demand_page(struct lg_cpu *cpu, unsigned long cr2, int errcode);
+bool demand_page(struct lg_cpu *cpu, unsigned long cr2, int errcode,
+		 unsigned long *iomem);
 void pin_page(struct lg_cpu *cpu, unsigned long vaddr);
 bool __guest_pa(struct lg_cpu *cpu, unsigned long vaddr, unsigned long *paddr);
 unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr);

drivers/lguest/lguest_user.c

@@ -385,7 +385,7 @@ static int initialize(struct file *file, const unsigned long __user *input)
 	/* "struct lguest" contains all we (the Host) know about a Guest. */
 	struct lguest *lg;
 	int err;
-	unsigned long args[3];
+	unsigned long args[4];
 
 	/*
 	 * We grab the Big Lguest lock, which protects against multiple
@@ -419,6 +419,7 @@ static int initialize(struct file *file, const unsigned long __user *input)
 	/* Populate the easy fields of our "struct lguest" */
 	lg->mem_base = (void __user *)args[0];
 	lg->pfn_limit = args[1];
+	lg->device_limit = args[3];
 
 	/* This is the first cpu (cpu 0) and it will start booting at args[2] */
 	err = lg_cpu_start(&lg->cpus[0], 0, args[2]);

drivers/lguest/page_tables.c

@@ -250,6 +250,16 @@ static void release_pte(pte_t pte)
 }
 /*:*/
 
+static bool gpte_in_iomem(struct lg_cpu *cpu, pte_t gpte)
+{
+	/* We don't handle large pages. */
+	if (pte_flags(gpte) & _PAGE_PSE)
+		return false;
+
+	return (pte_pfn(gpte) >= cpu->lg->pfn_limit
+		&& pte_pfn(gpte) < cpu->lg->device_limit);
+}
+
 static bool check_gpte(struct lg_cpu *cpu, pte_t gpte)
 {
 	if ((pte_flags(gpte) & _PAGE_PSE) ||
@@ -374,8 +384,14 @@ static pte_t *find_spte(struct lg_cpu *cpu, unsigned long vaddr, bool allocate,
  *
  * If we fixed up the fault (ie. we mapped the address), this routine returns
  * true.  Otherwise, it was a real fault and we need to tell the Guest.
+ *
+ * There's a corner case: they're trying to access memory between
+ * pfn_limit and device_limit, which is I/O memory.  In this case, we
+ * return false and set @iomem to the physical address, so the the
+ * Launcher can handle the instruction manually.
  */
-bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
+bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode,
+		 unsigned long *iomem)
 {
 	unsigned long gpte_ptr;
 	pte_t gpte;
@@ -383,6 +399,8 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
 	pmd_t gpmd;
 	pgd_t gpgd;
 
+	*iomem = 0;
+
 	/* We never demand page the Switcher, so trying is a mistake. */
 	if (vaddr >= switcher_addr)
 		return false;
@@ -459,6 +477,12 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
 	if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
 		return false;
 
+	/* If they're accessing io memory, we expect a fault. */
+	if (gpte_in_iomem(cpu, gpte)) {
+		*iomem = (pte_pfn(gpte) << PAGE_SHIFT) | (vaddr & ~PAGE_MASK);
+		return false;
+	}
+
 	/*
 	 * Check that the Guest PTE flags are OK, and the page number is below
 	 * the pfn_limit (ie. not mapping the Launcher binary).
@@ -553,7 +577,9 @@ static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
  */
 void pin_page(struct lg_cpu *cpu, unsigned long vaddr)
 {
-	if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2))
+	unsigned long iomem;
+
+	if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2, &iomem))
 		kill_guest(cpu, "bad stack page %#lx", vaddr);
 }
 /*:*/
@@ -928,7 +954,8 @@ static void __guest_set_pte(struct lg_cpu *cpu, int idx,
 			 * now.  This shaves 10% off a copy-on-write
 			 * micro-benchmark.
 			 */
-			if (pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
+			if ((pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED))
+			    && !gpte_in_iomem(cpu, gpte)) {
 				if (!check_gpte(cpu, gpte))
 					return;
 				set_pte(spte,

drivers/lguest/x86/core.c

@@ -362,9 +362,19 @@ static void setup_emulate_insn(struct lg_cpu *cpu)
 			sizeof(cpu->pending.insn));
 }
 
+static void setup_iomem_insn(struct lg_cpu *cpu, unsigned long iomem_addr)
+{
+	cpu->pending.trap = 14;
+	cpu->pending.addr = iomem_addr;
+	copy_from_guest(cpu, cpu->pending.insn, cpu->regs->eip,
+			sizeof(cpu->pending.insn));
+}
+
 /*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */
 void lguest_arch_handle_trap(struct lg_cpu *cpu)
 {
+	unsigned long iomem_addr;
+
 	switch (cpu->regs->trapnum) {
 	case 13: /* We've intercepted a General Protection Fault. */
 		/* Hand to Launcher to emulate those pesky IN and OUT insns */
@@ -385,8 +395,15 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu)
 		 * whether kernel or userspace code.
 		 */
 		if (demand_page(cpu, cpu->arch.last_pagefault,
-				cpu->regs->errcode))
+				cpu->regs->errcode, &iomem_addr))
+			return;
+
+		/* Was this an access to memory mapped IO? */
+		if (iomem_addr) {
+			/* Tell Launcher, let it handle it. */
+			setup_iomem_insn(cpu, iomem_addr);
 			return;
+		}
 
 		/*
 		 * OK, it's really not there (or not OK): the Guest needs to

tools/lguest/lguest.c

@@ -548,7 +548,8 @@ static void tell_kernel(unsigned long start)
 {
 	unsigned long args[] = { LHREQ_INITIALIZE,
 				 (unsigned long)guest_base,
-				 guest_limit / getpagesize(), start };
+				 guest_limit / getpagesize(), start,
+				 guest_limit / getpagesize() };
 	verbose("Guest: %p - %p (%#lx)\n",
 		guest_base, guest_base + guest_limit, guest_limit);
 	lguest_fd = open_or_die("/dev/lguest", O_RDWR);