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

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... 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>
This commit is contained in:
Andrew Cooper authored and Jan Beulich committed 2019-08-12 09:17:01 +02:00
1 parent 762b9a2d99
commit 60685089cb
6 files changed
+115 -39
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xen/arch/x86/Makefile
+1
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@@ -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
xen/arch/x86/boot/head.S
-1
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@@ -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>
xen/arch/x86/boot/x86_64.S
-33
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@@ -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
xen/arch/x86/desc.c
+109
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@@ -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:
*/
xen/include/asm-x86/desc.h
+1 -1
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@@ -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 {
xen/include/public/arch-x86/xen-x86_64.h
+4 -4
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@@ -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
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