x86/desc: Build boot_{,compat_}gdt[] in C

... where we can at least get the compiler to fill in the surrounding space
without having to do it manually.  This also results in the symbols having
proper type/size information in the debug symbols.

Reorder 'raw' in the seg_desc_t union to allow for easier initialisation.

Leave a comment explaining the various restrictions we have on altering the
GDT layout.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Introduce SEL2GDT(). Correct GDT indices in public header comments.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 5e3840084bae58115957a504dcea3c1f7325bece..2443fd2cc5bd227be0634c3138832d5cff5df3b3 100644 (file)
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -21,6 +21,7 @@ obj-$(CONFIG_PV) += compat.o x86_64/compat.o
 obj-$(CONFIG_KEXEC) += crash.o
 obj-y += debug.o
 obj-y += delay.o
+obj-y += desc.o
 obj-bin-y += dmi_scan.init.o
 obj-y += domctl.o
 obj-y += domain.o

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index ab2d52a79dd509d9404a8f726a92d755cf8c0a74..782deac0d433af816b5a4f0a75629f17f1de2045 100644 (file)
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -2,7 +2,6 @@
 #include <xen/multiboot2.h>
 #include <public/xen.h>
 #include <asm/asm_defns.h>
-#include <asm/desc.h>
 #include <asm/fixmap.h>
 #include <asm/page.h>
 #include <asm/processor.h>

diff --git a/xen/arch/x86/boot/x86_64.S b/xen/arch/x86/boot/x86_64.S
index 6853cc99c65283362983463427b130b3204b13bd..f762dfea11804cf27a9db9447a786e9ba2ce1294 100644 (file)
--- a/xen/arch/x86/boot/x86_64.S
+++ b/xen/arch/x86/boot/x86_64.S
@@ -43,44 +43,11 @@ ENTRY(__high_start)
 multiboot_ptr:
         .long   0
 
-        .word   0
-GLOBAL(boot_gdtr)
-        .word   LAST_RESERVED_GDT_BYTE
-        .quad   boot_gdt - FIRST_RESERVED_GDT_BYTE
-
 GLOBAL(stack_start)
         .quad   cpu0_stack
 
         .section .data.page_aligned, "aw", @progbits
         .align PAGE_SIZE, 0
-GLOBAL(boot_gdt)
-        .quad 0x0000000000000000     /* unused */
-        .quad 0x00af9b000000ffff     /* 0xe008 ring 0 code, 64-bit mode   */
-        .quad 0x00cf93000000ffff     /* 0xe010 ring 0 data                */
-        .quad 0x0000000000000000     /* reserved                          */
-        .quad 0x00cffb000000ffff     /* 0xe023 ring 3 code, compatibility */
-        .quad 0x00cff3000000ffff     /* 0xe02b ring 3 data                */
-        .quad 0x00affb000000ffff     /* 0xe033 ring 3 code, 64-bit mode   */
-        .quad 0x00cf9b000000ffff     /* 0xe038 ring 0 code, compatibility */
-        .fill (PER_CPU_GDT_ENTRY - __HYPERVISOR_CS32 / 8 - 1), 8, 0
-        .quad 0x0000910000000000     /* per-CPU entry (limit == cpu)      */
-
-        .align PAGE_SIZE, 0
-/* NB. Even rings != 0 get access to the full 4Gb, as only the            */
-/*     (compatibility) machine->physical mapping table lives there.       */
-GLOBAL(boot_compat_gdt)
-        .quad 0x0000000000000000     /* unused */
-        .quad 0x00af9b000000ffff     /* 0xe008 ring 0 code, 64-bit mode   */
-        .quad 0x00cf93000000ffff     /* 0xe010 ring 0 data                */
-        .quad 0x00cfbb000000ffff     /* 0xe019 ring 1 code, compatibility */
-        .quad 0x00cfb3000000ffff     /* 0xe021 ring 1 data                */
-        .quad 0x00cffb000000ffff     /* 0xe02b ring 3 code, compatibility */
-        .quad 0x00cff3000000ffff     /* 0xe033 ring 3 data                */
-        .quad 0x00cf9b000000ffff     /* 0xe038 ring 0 code, compatibility */
-        .fill (PER_CPU_GDT_ENTRY - __HYPERVISOR_CS32 / 8 - 1), 8, 0
-        .quad 0x0000910000000000     /* per-CPU entry (limit == cpu)      */
-        .align PAGE_SIZE, 0
-
 /*
  * Mapping of first 2 megabytes of memory. This is mapped with 4kB mappings
  * to avoid type conflicts with fixed-range MTRRs covering the lowest megabyte

diff --git a/xen/arch/x86/desc.c b/xen/arch/x86/desc.c
new file mode 100644 (file)
index 0000000..308aabe
--- /dev/null
+++ b/xen/arch/x86/desc.c
@@ -0,0 +1,109 @@
+#include <xen/init.h>
+#include <xen/lib.h>
+#include <xen/mm.h>
+#include <xen/percpu.h>
+
+#include <asm/desc.h>
+
+/*
+ * Native and Compat GDTs used by Xen.
+ *
+ * The R1 and R3 descriptors are fixed in Xen's ABI for PV guests.  All other
+ * descriptors are in principle variable, with the following restrictions.
+ *
+ * All R0 descriptors must line up in both GDTs to allow for correct
+ * interrupt/exception handling.
+ *
+ * The SYSCALL/SYSRET GDT layout requires:
+ *  - R0 long mode code followed by R0 data.
+ *  - R3 compat code, followed by R3 data, followed by R3 long mode code.
+ *
+ * The SYSENTER GDT layout requirements are compatible with SYSCALL.  Xen does
+ * not use the SYSEXIT instruction, and does not provide a compatible GDT.
+ *
+ * These tables are used directly by CPU0, and used as the template for the
+ * GDTs of other CPUs.  Everything from the TSS onwards is unique per CPU.
+ */
+
+#define SEL2GDT(sel) (((sel) >> 3) - FIRST_RESERVED_GDT_ENTRY)
+
+__section(".data.page_aligned") __aligned(PAGE_SIZE)
+seg_desc_t boot_gdt[PAGE_SIZE / sizeof(seg_desc_t)] =
+{
+    /* 0xe008 - Ring 0 code, 64bit mode */
+    [SEL2GDT(__HYPERVISOR_CS64)] =    { 0x00af9b000000ffff },
+
+    /* 0xe010 - Ring 0 data */
+    [SEL2GDT(__HYPERVISOR_DS32)] =    { 0x00cf93000000ffff },
+
+    /* 0xe018 - reserved */
+
+    /* 0xe023 - Ring 3 code, compatibility */
+    [SEL2GDT(FLAT_RING3_CS32)] =      { 0x00cffb000000ffff },
+
+    /* 0xe02b - Ring 3 data */
+    [SEL2GDT(FLAT_RING3_DS32)] =      { 0x00cff3000000ffff },
+
+    /* 0xe033 - Ring 3 code, 64-bit mode */
+    [SEL2GDT(FLAT_RING3_CS64)] =      { 0x00affb000000ffff },
+
+    /* 0xe038 - Ring 0 code, compatibility */
+    [SEL2GDT(__HYPERVISOR_CS32)] =    { 0x00cf9b000000ffff },
+
+    /* 0xe040 - TSS */
+    /* 0xe050 - LDT */
+
+    /* 0xe060 - per-CPU entry (limit == cpu) */
+    [SEL2GDT(PER_CPU_SELECTOR)] =     { 0x0000910000000000 },
+};
+
+__section(".data.page_aligned") __aligned(PAGE_SIZE)
+seg_desc_t boot_compat_gdt[PAGE_SIZE / sizeof(seg_desc_t)] =
+{
+    /* 0xe008 - Ring 0 code, 64bit mode */
+    [SEL2GDT(__HYPERVISOR_CS64)] =    { 0x00af9b000000ffff },
+
+    /* 0xe010 - Ring 0 data */
+    [SEL2GDT(__HYPERVISOR_DS32)] =    { 0x00cf93000000ffff },
+
+    /* 0xe019 - Ring 1 code, compatibility */
+    [SEL2GDT(FLAT_COMPAT_RING1_CS)] = { 0x00cfbb000000ffff },
+
+    /* 0xe021 - Ring 1 data */
+    [SEL2GDT(FLAT_COMPAT_RING1_DS)] = { 0x00cfb3000000ffff },
+
+    /* 0xe02b - Ring 3 code, compatibility */
+    [SEL2GDT(FLAT_COMPAT_RING3_CS)] = { 0x00cffb000000ffff },
+
+    /* 0xe033 - Ring 3 data */
+    [SEL2GDT(FLAT_COMPAT_RING3_DS)] = { 0x00cff3000000ffff },
+
+    /* 0xe038 - Ring 0 code, compatibility */
+    [SEL2GDT(__HYPERVISOR_CS32)] =    { 0x00cf9b000000ffff },
+
+    /* 0xe040 - TSS */
+    /* 0xe050 - LDT */
+
+    /* 0xe060 - per-CPU entry (limit == cpu) */
+    [SEL2GDT(PER_CPU_SELECTOR)] =     { 0x0000910000000000 },
+};
+
+/*
+ * Used by each CPU as it starts up, to enter C with a suitable %cs.
+ * References boot_cpu_gdt_table for a short period, until the CPUs switch
+ * onto their per-CPU GDTs.
+ */
+struct desc_ptr boot_gdtr = {
+    .limit = LAST_RESERVED_GDT_BYTE,
+    .base = (unsigned long)(boot_gdt - FIRST_RESERVED_GDT_ENTRY),
+};
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */

diff --git a/xen/include/asm-x86/desc.h b/xen/include/asm-x86/desc.h
index 37e88732f4c58317b7fccc73710cb18bb3bfcb4e..b7e62ac2a4ee3f3398f91f026fae3c66d9311e03 100644 (file)
--- a/xen/include/asm-x86/desc.h
+++ b/xen/include/asm-x86/desc.h
@@ -107,10 +107,10 @@
 #define SYS_DESC_trap_gate    15
 
 typedef union {
+    uint64_t raw;
     struct {
         uint32_t a, b;
     };
-    uint64_t raw;
 } seg_desc_t;
 
 typedef union {

diff --git a/xen/include/public/arch-x86/xen-x86_64.h b/xen/include/public/arch-x86/xen-x86_64.h
index 064b4aae70135cc671ffdd7a6d0c892149a493be..342eabc957c4228458cd6778418f1f01ba36a10b 100644 (file)
--- a/xen/include/public/arch-x86/xen-x86_64.h
+++ b/xen/include/public/arch-x86/xen-x86_64.h
@@ -44,11 +44,11 @@
  */
 
 #define FLAT_RING3_CS32 0xe023  /* GDT index 260 */
-#define FLAT_RING3_CS64 0xe033  /* GDT index 261 */
-#define FLAT_RING3_DS32 0xe02b  /* GDT index 262 */
+#define FLAT_RING3_CS64 0xe033  /* GDT index 262 */
+#define FLAT_RING3_DS32 0xe02b  /* GDT index 261 */
 #define FLAT_RING3_DS64 0x0000  /* NULL selector */
-#define FLAT_RING3_SS32 0xe02b  /* GDT index 262 */
-#define FLAT_RING3_SS64 0xe02b  /* GDT index 262 */
+#define FLAT_RING3_SS32 0xe02b  /* GDT index 261 */
+#define FLAT_RING3_SS64 0xe02b  /* GDT index 261 */
 
 #define FLAT_KERNEL_DS64 FLAT_RING3_DS64
 #define FLAT_KERNEL_DS32 FLAT_RING3_DS32