xen/x86: Use memblock_reserve for sensitive areas.

instead of a big memblock_reserve. This way we can be more
selective in freeing regions (and it also makes it easier
to understand where is what).

[v1: Move the auto_translate_physmap to proper line]
[v2: Per Stefano suggestion add more comments]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

3 files changed, 53 insertions, 9 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index ff962d4b821e..e532eb50e8d7 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -998,7 +998,54 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
 
         return ret;
 }
+/*
+ * If the MFN is not in the m2p (provided to us by the hypervisor) this
+ * function won't do anything. In practice this means that the XenBus
+ * MFN won't be available for the initial domain. */
+static void __init xen_reserve_mfn(unsigned long mfn)
+{
+        unsigned long pfn;
+
+        if (!mfn)
+                return;
+        pfn = mfn_to_pfn(mfn);
+        if (phys_to_machine_mapping_valid(pfn))
+                memblock_reserve(PFN_PHYS(pfn), PAGE_SIZE);
+}
+static void __init xen_reserve_internals(void)
+{
+        unsigned long size;
+
+        if (!xen_pv_domain())
+                return;
+
+        /* xen_start_info does not exist in the M2P, hence can't use
+         * xen_reserve_mfn. */
+        memblock_reserve(__pa(xen_start_info), PAGE_SIZE);
+
+        xen_reserve_mfn(PFN_DOWN(xen_start_info->shared_info));
+        xen_reserve_mfn(xen_start_info->store_mfn);
 
+        if (!xen_initial_domain())
+                xen_reserve_mfn(xen_start_info->console.domU.mfn);
+
+        if (xen_feature(XENFEAT_auto_translated_physmap))
+                return;
+
+        /*
+         * ALIGN up to compensate for the p2m_page pointing to an array that
+         * can partially filled (look in xen_build_dynamic_phys_to_machine).
+         */
+
+        size = PAGE_ALIGN(xen_start_info->nr_pages * sizeof(unsigned long));
+
+        /* We could use xen_reserve_mfn here, but would end up looping quite
+         * a lot (and call memblock_reserve for each PAGE), so lets just use
+         * the easy way and reserve it wholesale. */
+        memblock_reserve(__pa(xen_start_info->mfn_list), size);
+
+        /* The pagetables are reserved in mmu.c */
+}
 void xen_setup_shared_info(void)
 {
         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
@@ -1362,6 +1409,7 @@ asmlinkage void __init xen_start_kernel(void)
         xen_raw_console_write("mapping kernel into physical memory\n");
         pgd = xen_setup_kernel_pagetable(pgd, xen_start_info->nr_pages);
 
+        xen_reserve_internals();
         /* Allocate and initialize top and mid mfn levels for p2m structure */
         xen_build_mfn_list_list();
 
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index e4adbfbdfada..6a2bfa43c8a1 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -388,6 +388,11 @@ void __init xen_build_dynamic_phys_to_machine(void)
         }
 
         m2p_override_init();
+
+        /* NOTE: We cannot call memblock_reserve here for the mfn_list as there
+         * isn't enough pieces to make it work (for one - we are still using the
+         * Xen provided pagetable). Do it later in xen_reserve_internals.
+         */
 }
 
 unsigned long get_phys_to_machine(unsigned long pfn)
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index a4790bf22c59..9efca750405d 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -424,15 +424,6 @@ char * __init xen_memory_setup(void)
         e820_add_region(ISA_START_ADDRESS, ISA_END_ADDRESS - ISA_START_ADDRESS,
                         E820_RESERVED);
 
-        /*
-         * Reserve Xen bits:
-         *  - mfn_list
-         *  - xen_start_info
-         * See comment above "struct start_info" in <xen/interface/xen.h>
-         */
-        memblock_reserve(__pa(xen_start_info->mfn_list),
-                         xen_start_info->pt_base - xen_start_info->mfn_list);
-
         sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
         return "Xen";