Merge tag 'for-linus-6.10a-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull xen updates from Juergen Gross:

 - a small cleanup in the drivers/xen/xenbus Makefile

 - a fix of the Xen xenstore driver to improve connecting to a late
   started Xenstore

 - an enhancement for better support of ballooning in PVH guests

 - a cleanup using try_cmpxchg() instead of open coding it

* tag 'for-linus-6.10a-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  drivers/xen: Improve the late XenStore init protocol
  xen/xenbus: Use *-y instead of *-objs in Makefile
  xen/x86: add extra pages to unpopulated-alloc if available
  locking/x86/xen: Use try_cmpxchg() in xen_alloc_p2m_entry()

2 files changed, 38 insertions, 6 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 5f3a69f6ec34..0305485edcd3 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -379,3 +379,36 @@ void __init xen_add_extra_mem(unsigned long start_pfn, unsigned long n_pfns)
 
 	memblock_reserve(PFN_PHYS(start_pfn), PFN_PHYS(n_pfns));
 }
+
+#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
+int __init arch_xen_unpopulated_init(struct resource **res)
+{
+	unsigned int i;
+
+	if (!xen_domain())
+		return -ENODEV;
+
+	/* Must be set strictly before calling xen_free_unpopulated_pages(). */
+	*res = &iomem_resource;
+
+	/*
+	 * Initialize with pages from the extra memory regions (see
+	 * arch/x86/xen/setup.c).
+	 */
+	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
+		unsigned int j;
+
+		for (j = 0; j < xen_extra_mem[i].n_pfns; j++) {
+			struct page *pg =
+				pfn_to_page(xen_extra_mem[i].start_pfn + j);
+
+			xen_free_unpopulated_pages(1, &pg);
+		}
+
+		/* Zero so region is not also added to the balloon driver. */
+		xen_extra_mem[i].n_pfns = 0;
+	}
+
+	return 0;
+}
+#endif
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 9bdc3b656b2c..99918beccd80 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -555,7 +555,6 @@ int xen_alloc_p2m_entry(unsigned long pfn)
 			/* Separately check the mid mfn level */
 			unsigned long missing_mfn;
 			unsigned long mid_mfn_mfn;
-			unsigned long old_mfn;
 
 			mid_mfn = alloc_p2m_page();
 			if (!mid_mfn)
@@ -565,12 +564,12 @@ int xen_alloc_p2m_entry(unsigned long pfn)
 
 			missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);
 			mid_mfn_mfn = virt_to_mfn(mid_mfn);
-			old_mfn = cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn);
-			if (old_mfn != missing_mfn) {
-				free_p2m_page(mid_mfn);
-				mid_mfn = mfn_to_virt(old_mfn);
-			} else {
+			/* try_cmpxchg() updates missing_mfn on failure. */
+			if (try_cmpxchg(top_mfn_p, &missing_mfn, mid_mfn_mfn)) {
 				p2m_top_mfn_p[topidx] = mid_mfn;
+			} else {
+				free_p2m_page(mid_mfn);
+				mid_mfn = mfn_to_virt(missing_mfn);
 			}
 		}
 	} else {