Three bug-fixes:

- Revert the kexec fix which caused on non-kexec shutdowns a race.
  - Reuse existing P2M leafs - instead of requiring to allocate a large
    area of bootup virtual address estate.
  - Fix a one-off error when adding PFNs for balloon pages.
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Merge tag 'stable/for-linus-3.6-rc3-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen

Pull three xen bug-fixes from Konrad Rzeszutek Wilk:
 - Revert the kexec fix which caused on non-kexec shutdowns a race.
 - Reuse existing P2M leafs - instead of requiring to allocate a large
   area of bootup virtual address estate.
 - Fix a one-off error when adding PFNs for balloon pages.

* tag 'stable/for-linus-3.6-rc3-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen:
  xen/setup: Fix one-off error when adding for-balloon PFNs to the P2M.
  xen/p2m: Reuse existing P2M leafs if they are filled with 1:1 PFNs or INVALID.
  Revert "xen PVonHVM: move shared_info to MMIO before kexec"

arch/x86/xen/enlighten.c

@@ -31,7 +31,6 @@
 #include <linux/pci.h>
 #include <linux/gfp.h>
 #include <linux/memblock.h>
-#include <linux/syscore_ops.h>
 
 #include <xen/xen.h>
 #include <xen/interface/xen.h>
@@ -1470,130 +1469,38 @@ asmlinkage void __init xen_start_kernel(void)
 #endif
 }
 
-#ifdef CONFIG_XEN_PVHVM
+void __ref xen_hvm_init_shared_info(void)
-/*
- * The pfn containing the shared_info is located somewhere in RAM. This
- * will cause trouble if the current kernel is doing a kexec boot into a
- * new kernel. The new kernel (and its startup code) can not know where
- * the pfn is, so it can not reserve the page. The hypervisor will
- * continue to update the pfn, and as a result memory corruption occours
- * in the new kernel.
- *
- * One way to work around this issue is to allocate a page in the
- * xen-platform pci device's BAR memory range. But pci init is done very
- * late and the shared_info page is already in use very early to read
- * the pvclock. So moving the pfn from RAM to MMIO is racy because some
- * code paths on other vcpus could access the pfn during the small
- * window when the old pfn is moved to the new pfn. There is even a
- * small window were the old pfn is not backed by a mfn, and during that
- * time all reads return -1.
- *
- * Because it is not known upfront where the MMIO region is located it
- * can not be used right from the start in xen_hvm_init_shared_info.
- *
- * To minimise trouble the move of the pfn is done shortly before kexec.
- * This does not eliminate the race because all vcpus are still online
- * when the syscore_ops will be called. But hopefully there is no work
- * pending at this point in time. Also the syscore_op is run last which
- * reduces the risk further.
- */
-
-static struct shared_info *xen_hvm_shared_info;
-
-static void xen_hvm_connect_shared_info(unsigned long pfn)
 {
+	int cpu;
 	struct xen_add_to_physmap xatp;
+	static struct shared_info *shared_info_page = 0;
 
+	if (!shared_info_page)
+		shared_info_page = (struct shared_info *)
+			extend_brk(PAGE_SIZE, PAGE_SIZE);
 	xatp.domid = DOMID_SELF;
 	xatp.idx = 0;
 	xatp.space = XENMAPSPACE_shared_info;
-	xatp.gpfn = pfn;
+	xatp.gpfn = __pa(shared_info_page) >> PAGE_SHIFT;
 	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
 		BUG();
 
-}
+	HYPERVISOR_shared_info = (struct shared_info *)shared_info_page;
-static void xen_hvm_set_shared_info(struct shared_info *sip)
-{
-	int cpu;
-
-	HYPERVISOR_shared_info = sip;
 
 	/* xen_vcpu is a pointer to the vcpu_info struct in the shared_info
 	 * page, we use it in the event channel upcall and in some pvclock
 	 * related functions. We don't need the vcpu_info placement
 	 * optimizations because we don't use any pv_mmu or pv_irq op on
 	 * HVM.
-	 * When xen_hvm_set_shared_info is run at boot time only vcpu 0 is
+	 * When xen_hvm_init_shared_info is run at boot time only vcpu 0 is
-	 * online but xen_hvm_set_shared_info is run at resume time too and
+	 * online but xen_hvm_init_shared_info is run at resume time too and
 	 * in that case multiple vcpus might be online. */
 	for_each_online_cpu(cpu) {
 		per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
 	}
 }
 
-/* Reconnect the shared_info pfn to a mfn */
+#ifdef CONFIG_XEN_PVHVM
-void xen_hvm_resume_shared_info(void)
-{
-	xen_hvm_connect_shared_info(__pa(xen_hvm_shared_info) >> PAGE_SHIFT);
-}
-
-#ifdef CONFIG_KEXEC
-static struct shared_info *xen_hvm_shared_info_kexec;
-static unsigned long xen_hvm_shared_info_pfn_kexec;
-
-/* Remember a pfn in MMIO space for kexec reboot */
-void __devinit xen_hvm_prepare_kexec(struct shared_info *sip, unsigned long pfn)
-{
-	xen_hvm_shared_info_kexec = sip;
-	xen_hvm_shared_info_pfn_kexec = pfn;
-}
-
-static void xen_hvm_syscore_shutdown(void)
-{
-	struct xen_memory_reservation reservation = {
-		.domid = DOMID_SELF,
-		.nr_extents = 1,
-	};
-	unsigned long prev_pfn;
-	int rc;
-
-	if (!xen_hvm_shared_info_kexec)
-		return;
-
-	prev_pfn = __pa(xen_hvm_shared_info) >> PAGE_SHIFT;
-	set_xen_guest_handle(reservation.extent_start, &prev_pfn);
-
-	/* Move pfn to MMIO, disconnects previous pfn from mfn */
-	xen_hvm_connect_shared_info(xen_hvm_shared_info_pfn_kexec);
-
-	/* Update pointers, following hypercall is also a memory barrier */
-	xen_hvm_set_shared_info(xen_hvm_shared_info_kexec);
-
-	/* Allocate new mfn for previous pfn */
-	do {
-		rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
-		if (rc == 0)
-			msleep(123);
-	} while (rc == 0);
-
-	/* Make sure the previous pfn is really connected to a (new) mfn */
-	BUG_ON(rc != 1);
-}
-
-static struct syscore_ops xen_hvm_syscore_ops = {
-	.shutdown = xen_hvm_syscore_shutdown,
-};
-#endif
-
-/* Use a pfn in RAM, may move to MMIO before kexec. */
-static void __init xen_hvm_init_shared_info(void)
-{
-	/* Remember pointer for resume */
-	xen_hvm_shared_info = extend_brk(PAGE_SIZE, PAGE_SIZE);
-	xen_hvm_connect_shared_info(__pa(xen_hvm_shared_info) >> PAGE_SHIFT);
-	xen_hvm_set_shared_info(xen_hvm_shared_info);
-}
-
 static void __init init_hvm_pv_info(void)
 {
 	int major, minor;
@@ -1644,9 +1551,6 @@ static void __init xen_hvm_guest_init(void)
 	init_hvm_pv_info();
 
 	xen_hvm_init_shared_info();
-#ifdef CONFIG_KEXEC
-	register_syscore_ops(&xen_hvm_syscore_ops);
-#endif
 
 	if (xen_feature(XENFEAT_hvm_callback_vector))
 		xen_have_vector_callback = 1;

arch/x86/xen/p2m.c

@@ -196,9 +196,11 @@ RESERVE_BRK(p2m_mid_identity, PAGE_SIZE * 2 * 3);
 
 /* When we populate back during bootup, the amount of pages can vary. The
  * max we have is seen is 395979, but that does not mean it can't be more.
- * But some machines can have 3GB I/O holes even. So lets reserve enough
+ * Some machines can have 3GB I/O holes even. With early_can_reuse_p2m_middle
- * for 4GB of I/O and E820 holes. */
+ * it can re-use Xen provided mfn_list array, so we only need to allocate at
-RESERVE_BRK(p2m_populated, PMD_SIZE * 4);
+ * most three P2M top nodes. */
+RESERVE_BRK(p2m_populated, PAGE_SIZE * 3);
+
 static inline unsigned p2m_top_index(unsigned long pfn)
 {
 	BUG_ON(pfn >= MAX_P2M_PFN);
@@ -575,12 +577,99 @@ static bool __init early_alloc_p2m(unsigned long pfn)
 	}
 	return true;
 }
+
+/*
+ * Skim over the P2M tree looking at pages that are either filled with
+ * INVALID_P2M_ENTRY or with 1:1 PFNs. If found, re-use that page and
+ * replace the P2M leaf with a p2m_missing or p2m_identity.
+ * Stick the old page in the new P2M tree location.
+ */
+bool __init early_can_reuse_p2m_middle(unsigned long set_pfn, unsigned long set_mfn)
+{
+	unsigned topidx;
+	unsigned mididx;
+	unsigned ident_pfns;
+	unsigned inv_pfns;
+	unsigned long *p2m;
+	unsigned long *mid_mfn_p;
+	unsigned idx;
+	unsigned long pfn;
+
+	/* We only look when this entails a P2M middle layer */
+	if (p2m_index(set_pfn))
+		return false;
+
+	for (pfn = 0; pfn <= MAX_DOMAIN_PAGES; pfn += P2M_PER_PAGE) {
+		topidx = p2m_top_index(pfn);
+
+		if (!p2m_top[topidx])
+			continue;
+
+		if (p2m_top[topidx] == p2m_mid_missing)
+			continue;
+
+		mididx = p2m_mid_index(pfn);
+		p2m = p2m_top[topidx][mididx];
+		if (!p2m)
+			continue;
+
+		if ((p2m == p2m_missing) || (p2m == p2m_identity))
+			continue;
+
+		if ((unsigned long)p2m == INVALID_P2M_ENTRY)
+			continue;
+
+		ident_pfns = 0;
+		inv_pfns = 0;
+		for (idx = 0; idx < P2M_PER_PAGE; idx++) {
+			/* IDENTITY_PFNs are 1:1 */
+			if (p2m[idx] == IDENTITY_FRAME(pfn + idx))
+				ident_pfns++;
+			else if (p2m[idx] == INVALID_P2M_ENTRY)
+				inv_pfns++;
+			else
+				break;
+		}
+		if ((ident_pfns == P2M_PER_PAGE) || (inv_pfns == P2M_PER_PAGE))
+			goto found;
+	}
+	return false;
+found:
+	/* Found one, replace old with p2m_identity or p2m_missing */
+	p2m_top[topidx][mididx] = (ident_pfns ? p2m_identity : p2m_missing);
+	/* And the other for save/restore.. */
+	mid_mfn_p = p2m_top_mfn_p[topidx];
+	/* NOTE: Even if it is a p2m_identity it should still be point to
+	 * a page filled with INVALID_P2M_ENTRY entries. */
+	mid_mfn_p[mididx] = virt_to_mfn(p2m_missing);
+
+	/* Reset where we want to stick the old page in. */
+	topidx = p2m_top_index(set_pfn);
+	mididx = p2m_mid_index(set_pfn);
+
+	/* This shouldn't happen */
+	if (WARN_ON(p2m_top[topidx] == p2m_mid_missing))
+		early_alloc_p2m(set_pfn);
+
+	if (WARN_ON(p2m_top[topidx][mididx] != p2m_missing))
+		return false;
+
+	p2m_init(p2m);
+	p2m_top[topidx][mididx] = p2m;
+	mid_mfn_p = p2m_top_mfn_p[topidx];
+	mid_mfn_p[mididx] = virt_to_mfn(p2m);
+
+	return true;
+}
 bool __init early_set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
 	if (unlikely(!__set_phys_to_machine(pfn, mfn)))  {
 		if (!early_alloc_p2m(pfn))
 			return false;
 
+		if (early_can_reuse_p2m_middle(pfn, mfn))
+			return __set_phys_to_machine(pfn, mfn);
+
 		if (!early_alloc_p2m_middle(pfn, false /* boundary crossover OK!*/))
 			return false;
 

arch/x86/xen/setup.c

@@ -78,9 +78,16 @@ static void __init xen_add_extra_mem(u64 start, u64 size)
 	memblock_reserve(start, size);
 
 	xen_max_p2m_pfn = PFN_DOWN(start + size);
+	for (pfn = PFN_DOWN(start); pfn < xen_max_p2m_pfn; pfn++) {
+		unsigned long mfn = pfn_to_mfn(pfn);
+
+		if (WARN(mfn == pfn, "Trying to over-write 1-1 mapping (pfn: %lx)\n", pfn))
+			continue;
+		WARN(mfn != INVALID_P2M_ENTRY, "Trying to remove %lx which has %lx mfn!\n",
+			pfn, mfn);
 
-	for (pfn = PFN_DOWN(start); pfn <= xen_max_p2m_pfn; pfn++)
 		__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+	}
 }
 
 static unsigned long __init xen_do_chunk(unsigned long start,

arch/x86/xen/suspend.c

@@ -30,7 +30,7 @@ void xen_arch_hvm_post_suspend(int suspend_cancelled)
 {
 #ifdef CONFIG_XEN_PVHVM
 	int cpu;
-	xen_hvm_resume_shared_info();
+	xen_hvm_init_shared_info();
 	xen_callback_vector();
 	xen_unplug_emulated_devices();
 	if (xen_feature(XENFEAT_hvm_safe_pvclock)) {

arch/x86/xen/xen-ops.h

@@ -41,7 +41,7 @@ void xen_enable_syscall(void);
 void xen_vcpu_restore(void);
 
 void xen_callback_vector(void);
-void xen_hvm_resume_shared_info(void);
+void xen_hvm_init_shared_info(void);
 void xen_unplug_emulated_devices(void);
 
 void __init xen_build_dynamic_phys_to_machine(void);

drivers/xen/platform-pci.c

@@ -101,19 +101,6 @@ static int platform_pci_resume(struct pci_dev *pdev)
 	return 0;
 }
 
-static void __devinit prepare_shared_info(void)
-{
-#ifdef CONFIG_KEXEC
-	unsigned long addr;
-	struct shared_info *hvm_shared_info;
-
-	addr = alloc_xen_mmio(PAGE_SIZE);
-	hvm_shared_info = ioremap(addr, PAGE_SIZE);
-	memset(hvm_shared_info, 0, PAGE_SIZE);
-	xen_hvm_prepare_kexec(hvm_shared_info, addr >> PAGE_SHIFT);
-#endif
-}
-
 static int __devinit platform_pci_init(struct pci_dev *pdev,
 				       const struct pci_device_id *ent)
 {
@@ -151,8 +138,6 @@ static int __devinit platform_pci_init(struct pci_dev *pdev,
 	platform_mmio = mmio_addr;
 	platform_mmiolen = mmio_len;
 
-	prepare_shared_info();
-
 	if (!xen_have_vector_callback) {
 		ret = xen_allocate_irq(pdev);
 		if (ret) {

include/xen/events.h

@@ -58,8 +58,6 @@ void notify_remote_via_irq(int irq);
 
 void xen_irq_resume(void);
 
-void xen_hvm_prepare_kexec(struct shared_info *sip, unsigned long pfn);
-
 /* Clear an irq's pending state, in preparation for polling on it */
 void xen_clear_irq_pending(int irq);
 void xen_set_irq_pending(int irq);