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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v2 2/2] x86/desc: Build boot_{, compat_}gdt[] in C
From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
... 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@xxxxxxxxxx>
Introduce SEL2GDT(). Correct GDT indices in public header.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Address my own v1 review comments. Re-base.
---
There is plenty more cleanup which can be done in the future. As we are
64-bit, there is no need for load_TR() to keep the TSS in sync between the two
GDTs, which means it can drop all sgdt/lgdt instructions. Also,
__HYPERVISOR_CS32 is unused and could be dropped.
As is demonstrated by the required includes, asm/desc.h is a tangle in need of
some cleanup.
The SYSEXIT GDT requirements are:
R0 long code, R0 data, R3 compat code, R3 data, R3 long code, R3 data.
We could make Xen compatible by shifting the R0 code/data down by one slot,
moving R0 compat code elsewhere and replacing it with another R3 data.
However, this seems like a fairly pointless exercise, as the only thing it
will do is change the magic numbers which developers have become accustom to
seeing in backtraces.
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -21,6 +21,7 @@ obj-$(CONFIG_PV) += compat.o x86_64/comp
obj-$(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
--- 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>
--- 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
--- /dev/null
+++ b/xen/arch/x86/desc.c
@@ -0,0 +1,109 @@
+#include <xen/types.h>
+#include <xen/lib.h>
+#include <xen/percpu.h>
+#include <xen/mm.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_GDT_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_GDT_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:
+ */
--- 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 {
--- 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_DS32 0xe02b /* GDT index 261 */ +#define FLAT_RING3_CS64 0xe033 /* GDT index 262 */ #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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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