[Xen-devel] [PATCH v7 03/10] x86: provide executable fixmap facility

[Wei Liu <wl@xen.org>]

This allows us to set aside some address space for executable mapping.
This fixed map range starts from XEN_VIRT_END so that it is within reach
of the .text section.

Shift the percpu stub range and shrink livepatch range accordingly.

Signed-off-by: Wei Liu <liuwe@microsoft.com>
---
v7:
1. Introduce ASM_CONSTANT

v6:
1. Move symbol generation snippet to arch_init_memory and use %P0

v5:
1. drop __virt_to_fix_x
2. also check FIX*_RESERVED in __set_fixmap*
3. generate global symbol to be used in linker script
4. address other misc comments
---
 xen/arch/x86/boot/x86_64.S      | 15 ++++++++++++---
 xen/arch/x86/livepatch.c        |  3 ++-
 xen/arch/x86/mm.c               | 14 +++++++++++++-
 xen/arch/x86/smpboot.c          |  2 +-
 xen/arch/x86/xen.lds.S          |  1 +
 xen/include/asm-x86/asm_defns.h |  5 +++++
 xen/include/asm-x86/config.h    |  2 +-
 xen/include/asm-x86/fixmap.h    | 24 ++++++++++++++++++++++++
 8 files changed, 59 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/boot/x86_64.S b/xen/arch/x86/boot/x86_64.S
index 1cbf5acdfb..314a32a19f 100644
--- a/xen/arch/x86/boot/x86_64.S
+++ b/xen/arch/x86/boot/x86_64.S
@@ -81,11 +81,20 @@ GLOBAL(l2_directmap)
         .size l2_directmap, . - l2_directmap
 
 /*
- * L2 mapping the Xen text/data/bss region, constructed dynamically.  Uses 1x
- * 4k page.
+ * L2 mapping the Xen text/data/bss region, constructed dynamically.
+ * Executable fixmap is hooked up statically.
+ * Uses 1x 4k page.
  */
 GLOBAL(l2_xenmap)
-        .fill L2_PAGETABLE_ENTRIES, 8, 0
+        idx = 0
+        .rept L2_PAGETABLE_ENTRIES
+        .if idx == l2_table_offset(FIXADDR_X_TOP - 1)
+        .quad sym_offs(l1_fixmap_x) + __PAGE_HYPERVISOR
+        .else
+        .quad 0
+        .endif
+        idx = idx + 1
+        .endr
         .size l2_xenmap, . - l2_xenmap
 
 /* L2 mapping the fixmap.  Uses 1x 4k page. */
diff --git a/xen/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c
index 2749cbc5cf..513b0f3841 100644
--- a/xen/arch/x86/livepatch.c
+++ b/xen/arch/x86/livepatch.c
@@ -12,6 +12,7 @@
 #include <xen/livepatch.h>
 #include <xen/sched.h>
 
+#include <asm/fixmap.h>
 #include <asm/nmi.h>
 #include <asm/livepatch.h>
 
@@ -311,7 +312,7 @@ void __init arch_livepatch_init(void)
     void *start, *end;
 
     start = (void *)xen_virt_end;
-    end = (void *)(XEN_VIRT_END - NR_CPUS * PAGE_SIZE);
+    end = (void *)(XEN_VIRT_END - FIXADDR_X_SIZE - NR_CPUS * PAGE_SIZE);
 
     BUG_ON(end <= start);
 
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index a05a713276..9b33829084 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -158,6 +158,8 @@
 /* Mapping of the fixmap space needed early. */
 l1_pgentry_t __section(".bss.page_aligned") __aligned(PAGE_SIZE)
     l1_fixmap[L1_PAGETABLE_ENTRIES];
+l1_pgentry_t __section(".bss.page_aligned") __aligned(PAGE_SIZE)
+    l1_fixmap_x[L1_PAGETABLE_ENTRIES];
 
 paddr_t __read_mostly mem_hotplug;
 
@@ -373,6 +375,9 @@ void __init arch_init_memory(void)
         }
     }
 #endif
+
+    /* Generate a symbol to be used in linker script */
+    ASM_CONSTANT(FIXADDR_X_SIZE, FIXADDR_X_SIZE);
 }
 
 int page_is_ram_type(unsigned long mfn, unsigned long mem_type)
@@ -5719,10 +5724,17 @@ int destroy_xen_mappings(unsigned long s, unsigned long e)
 void __set_fixmap(
     enum fixed_addresses idx, unsigned long mfn, unsigned long flags)
 {
-    BUG_ON(idx >= __end_of_fixed_addresses);
+    BUG_ON(idx >= __end_of_fixed_addresses || idx <= FIX_RESERVED);
     map_pages_to_xen(__fix_to_virt(idx), _mfn(mfn), 1, flags);
 }
 
+void __set_fixmap_x(
+    enum fixed_addresses_x idx, unsigned long mfn, unsigned long flags)
+{
+    BUG_ON(idx >= __end_of_fixed_addresses_x || idx <= FIX_X_RESERVED);
+    map_pages_to_xen(__fix_x_to_virt(idx), _mfn(mfn), 1, flags);
+}
+
 void *__init arch_vmap_virt_end(void)
 {
     return fix_to_virt(__end_of_fixed_addresses);
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 93b86a09e9..e83e4564a4 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -644,7 +644,7 @@ unsigned long alloc_stub_page(unsigned int cpu, unsigned long *mfn)
         unmap_domain_page(memset(__map_domain_page(pg), 0xcc, PAGE_SIZE));
     }
 
-    stub_va = XEN_VIRT_END - (cpu + 1) * PAGE_SIZE;
+    stub_va = XEN_VIRT_END - FIXADDR_X_SIZE - (cpu + 1) * PAGE_SIZE;
     if ( map_pages_to_xen(stub_va, page_to_mfn(pg), 1,
                           PAGE_HYPERVISOR_RX | MAP_SMALL_PAGES) )
     {
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index f5730ffe93..44fda616d5 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -352,6 +352,7 @@ SECTIONS
 }
 
 ASSERT(__2M_rwdata_end <= XEN_VIRT_END - XEN_VIRT_START + __XEN_VIRT_START -
+                          FIXADDR_X_SIZE -
                           NR_CPUS * PAGE_SIZE,
        "Xen image overlaps stubs area")
 
diff --git a/xen/include/asm-x86/asm_defns.h b/xen/include/asm-x86/asm_defns.h
index 370f239c50..98cd49a89b 100644
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -392,4 +392,9 @@ label: .long (val);                         \
     .size label, . - label;                 \
     .type label, @object
 
+
+#define ASM_CONSTANT(name, value)                \
+    asm ( ".equ " #name ", %P0; .global " #name  \
+          :: "i" ((value)) );
+
 #endif /* __X86_ASM_DEFNS_H__ */
diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
index d0cfbb70a8..a34053c4c0 100644
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -218,7 +218,7 @@ extern unsigned char boot_edid_info[128];
 /* Slot 261: high read-only compat machine-to-phys conversion table (1GB). */
 #define HIRO_COMPAT_MPT_VIRT_START RDWR_COMPAT_MPT_VIRT_END
 #define HIRO_COMPAT_MPT_VIRT_END (HIRO_COMPAT_MPT_VIRT_START + GB(1))
-/* Slot 261: xen text, static data and bss (1GB). */
+/* Slot 261: xen text, static data, bss, per-cpu stubs and executable fixmap (1GB). */
 #define XEN_VIRT_START          (HIRO_COMPAT_MPT_VIRT_END)
 #define XEN_VIRT_END            (XEN_VIRT_START + GB(1))
 
diff --git a/xen/include/asm-x86/fixmap.h b/xen/include/asm-x86/fixmap.h
index 9fb2f47946..8330097a74 100644
--- a/xen/include/asm-x86/fixmap.h
+++ b/xen/include/asm-x86/fixmap.h
@@ -15,6 +15,7 @@
 #include <asm/page.h>
 
 #define FIXADDR_TOP (VMAP_VIRT_END - PAGE_SIZE)
+#define FIXADDR_X_TOP (XEN_VIRT_END - PAGE_SIZE)
 
 #ifndef __ASSEMBLY__
 
@@ -89,6 +90,29 @@ static inline unsigned long virt_to_fix(const unsigned long vaddr)
     return __virt_to_fix(vaddr);
 }
 
+enum fixed_addresses_x {
+    /* Index 0 is reserved since fix_x_to_virt(0) == FIXADDR_X_TOP. */
+    FIX_X_RESERVED,
+#ifdef CONFIG_HYPERV_GUEST
+    FIX_X_HYPERV_HCALL,
+#endif
+    __end_of_fixed_addresses_x
+};
+
+#define FIXADDR_X_SIZE  (__end_of_fixed_addresses_x << PAGE_SHIFT)
+#define FIXADDR_X_START (FIXADDR_X_TOP - FIXADDR_X_SIZE)
+
+extern void __set_fixmap_x(
+    enum fixed_addresses_x idx, unsigned long mfn, unsigned long flags);
+
+#define set_fixmap_x(idx, phys) \
+    __set_fixmap_x(idx, (phys)>>PAGE_SHIFT, PAGE_HYPERVISOR_RX | MAP_SMALL_PAGES)
+
+#define clear_fixmap_x(idx) __set_fixmap_x(idx, 0, 0)
+
+#define __fix_x_to_virt(x) (FIXADDR_X_TOP - ((x) << PAGE_SHIFT))
+#define fix_x_to_virt(x)   ((void *)__fix_x_to_virt(x))
+
 #endif /* __ASSEMBLY__ */
 
 #endif
-- 
2.20.1


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