[Qemu-devel] [RFC PATCH v2 11/12] pc: support direct loading protected/long mode kernel

[Chao Peng]

Traditionally a PC follows the following booting steps:

    QEMU -> BIOS -> bootloader -> kernel realmode code
         -> kernel protected/longmode code.

This process takes lots of time. For light virtualization platform we
let QEMU loads protected/long mode kernel directly, hence skipping
several steps and speeding up the whole booting. We do this by filling
the zero page per Linux booting protocol and then jumping to the kernel
protected/long mode entry. Registers and paging should also be put in
the correct state.

Signed-off-by: Jim Kukunas <address@hidden>
Signed-off-by: Chao Peng <address@hidden>
---
 hw/i386/pc.c | 166 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 163 insertions(+), 3 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index f479697..4a368de 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -85,6 +85,31 @@
 #define FW_CFG_E820_TABLE (FW_CFG_ARCH_LOCAL + 3)
 #define FW_CFG_HPET (FW_CFG_ARCH_LOCAL + 4)
 
+#define BOOT_GDT                0x500
+#define BOOT_IDT                0x520
+#define BOOT_GDT_NULL           0
+#define BOOT_GDT_CODE           1
+#define BOOT_GDT_DATA           2
+#define BOOT_GDT_TSS            3
+#define BOOT_GDT_MAX            4
+#define BOOT_GDT_FLAGS_CODE     (DESC_P_MASK | DESC_S_MASK | DESC_CS_MASK | \
+                                 DESC_R_MASK | DESC_A_MASK | DESC_G_MASK )
+#define BOOT_GDT_FLAGS_DATA     (DESC_P_MASK | DESC_S_MASK | DESC_W_MASK |  \
+                                 DESC_A_MASK | DESC_B_MASK | DESC_G_MASK)
+#define BOOT_GDT_FLAGS_TSS      DESC_P_MASK | (11 << DESC_TYPE_SHIFT)
+#define BOOT_PML4               0x9000
+#define BOOT_PDPTE              0xA000
+#define BOOT_LOADER_SP          0x8000
+#define BOOT_CMDLINE_OFFSET     0x20000
+#define BOOT_ZEROPAGE_OFFSET    0x7000
+
+#define GDT_ENTRY(flags, base, limit)               \
+       ((((base)  & 0xff000000ULL) << (56-24)) |    \
+       (((flags) & 0x0000f0ffULL) << 40) |          \
+       (((limit) & 0x000f0000ULL) << (48-16)) |     \
+       (((base)  & 0x00ffffffULL) << 16) |          \
+       (((limit) & 0x0000ffffULL)))
+
 #define E820_NR_ENTRIES                16
 
 struct e820_entry {
@@ -98,6 +123,13 @@ struct e820_table {
     struct e820_entry entry[E820_NR_ENTRIES];
 } QEMU_PACKED __attribute((__aligned__(4)));
 
+struct kernel_boot_info {
+    uint64_t entry;
+    bool protected_mode;
+    bool long_mode;
+};
+
+static struct kernel_boot_info boot_info;
 static struct e820_table e820_reserve;
 static struct e820_entry *e820_table;
 static unsigned e820_entries;
@@ -665,6 +697,124 @@ bool e820_get_entry(int idx, uint32_t type, uint64_t 
*address, uint64_t *length)
     return false;
 }
 
+static void reset_cpu(CPUX86State *env)
+{
+    unsigned int flags = BOOT_GDT_FLAGS_CODE;
+
+    if (boot_info.long_mode) {
+        flags |= DESC_L_MASK;
+    }
+    cpu_x86_load_seg_cache(env, R_CS, BOOT_GDT_CODE * 8, 0, 0xfffff, flags);
+
+    cpu_x86_load_seg_cache(env, R_DS, BOOT_GDT_DATA * 8, 0, 0xfffff,
+                           BOOT_GDT_FLAGS_DATA);
+    cpu_x86_load_seg_cache(env, R_ES, BOOT_GDT_DATA * 8, 0, 0xfffff,
+                           BOOT_GDT_FLAGS_DATA);
+    cpu_x86_load_seg_cache(env, R_FS, BOOT_GDT_DATA * 8, 0, 0xfffff,
+                           BOOT_GDT_FLAGS_DATA);
+    cpu_x86_load_seg_cache(env, R_GS, BOOT_GDT_DATA * 8, 0, 0xfffff,
+                           BOOT_GDT_FLAGS_DATA);
+    cpu_x86_load_seg_cache(env, R_SS, BOOT_GDT_DATA * 8, 0, 0xfffff,
+                           BOOT_GDT_FLAGS_DATA);
+
+    env->gdt.base = BOOT_GDT;
+    env->gdt.limit = BOOT_GDT_MAX * 8 - 1;
+
+    env->idt.base = BOOT_IDT;
+
+    env->tr.selector = BOOT_GDT_TSS * 8;
+    env->tr.flags = BOOT_GDT_FLAGS_TSS;
+
+    env->cr[3] = BOOT_PML4;
+    env->cr[0] |= (CR0_PG_MASK | CR0_PE_MASK);
+
+    if (boot_info.long_mode) {
+        env->cr[4] |= CR4_PAE_MASK;
+        cpu_load_efer(env, env->efer | MSR_EFER_LME | MSR_EFER_LMA);
+    }
+
+    env->regs[R_ESP] = BOOT_LOADER_SP;
+    env->regs[R_ESI] = BOOT_ZEROPAGE_OFFSET;
+    env->eip = boot_info.entry;
+}
+
+static void setup_seg_desc_tables(void)
+{
+    uint64_t idt = 0;
+    uint64_t gdt[BOOT_GDT_MAX] = {
+             [BOOT_GDT_NULL] = GDT_ENTRY(0, 0, 0),
+             [BOOT_GDT_CODE] = GDT_ENTRY(BOOT_GDT_FLAGS_CODE, 0, 0xFFFFF),
+             [BOOT_GDT_DATA] = GDT_ENTRY(BOOT_GDT_FLAGS_DATA, 0, 0xFFFFF),
+             [BOOT_GDT_TSS ] = GDT_ENTRY(BOOT_GDT_FLAGS_TSS, 0, 0xFFFFF)
+            };
+
+    if (boot_info.long_mode) {
+        gdt[BOOT_GDT_CODE] |= (1UL << (32 + DESC_L_SHIFT));
+    }
+
+    cpu_physical_memory_write((hwaddr)BOOT_GDT, gdt, sizeof(gdt));
+    cpu_physical_memory_write((hwaddr)BOOT_IDT, &idt, sizeof(idt));
+}
+
+static void setup_page_tables(void)
+{
+    void *p;
+    size_t len = 4096;
+
+    p = cpu_physical_memory_map(BOOT_PML4, &len, 1);
+    memset(p, 0, 4096);
+    *(uint64_t*)p = (uint64_t)(BOOT_PDPTE | 3);
+    cpu_physical_memory_unmap(p, len, 1, len);
+
+    len = 4096;
+    p = cpu_physical_memory_map(BOOT_PDPTE, &len, 1);
+    memset(p, 0, 4096);
+    *(uint64_t*)p = 0x83;
+    cpu_physical_memory_unmap(p, len, 1, len);
+}
+
+static void setup_kernel_zero_page(void)
+{
+    int i;
+    uint8_t *zero_page;
+    void *e820_map;
+    size_t zero_page_size = 4096;
+    MachineState *machine = MACHINE(qdev_get_machine());
+    size_t cmdline_size = strlen(machine->kernel_cmdline) + 1;
+
+    cpu_physical_memory_write((hwaddr)BOOT_CMDLINE_OFFSET,
+                               machine->kernel_cmdline, cmdline_size);
+
+    zero_page = cpu_physical_memory_map((hwaddr)BOOT_ZEROPAGE_OFFSET,
+                                        &zero_page_size, 1);
+    memset(zero_page, 0, zero_page_size);
+
+    /* hdr.type_of_loader */
+    zero_page[0x210] = 0xFF;
+    /* hdr.boot_flag */
+    stw_p(zero_page + 0x1fe, 0xAA55);
+    /* hdr.header */
+    stl_p(zero_page + 0x202, 0x53726448);
+    /* hdr.cmd_line_ptr */
+    stl_p(zero_page + 0x228, BOOT_CMDLINE_OFFSET);
+    /* hdr.cmdline_size */
+    stl_p(zero_page + 0x238, cmdline_size);
+    /* e820_entries */
+    zero_page[0x1e8] = e820_entries;
+    /* e820_map */
+    e820_map = zero_page + 0x2d0;
+    for (i = 0; i < e820_entries; i++) {
+        stq_p(e820_map, e820_table[i].address);
+        e820_map += 8;
+        stq_p(e820_map, e820_table[i].length);
+        e820_map += 8;
+        stl_p(e820_map, e820_table[i].type);
+        e820_map += 4;
+    }
+
+    cpu_physical_memory_unmap(zero_page, zero_page_size, 1, zero_page_size);
+}
+
 /* Enables contiguous-apic-ID mode, for compatibility */
 static bool compat_apic_id_mode;
 
@@ -2206,15 +2356,25 @@ static void pc_machine_reset(void)
 
     qemu_devices_reset();
 
-    /* Reset APIC after devices have been reset to cancel
-     * any changes that qemu_devices_reset() might have done.
-     */
     CPU_FOREACH(cs) {
         cpu = X86_CPU(cs);
 
+        /* Reset APIC after devices have been reset to cancel
+         * any changes that qemu_devices_reset() might have done.
+         */
         if (cpu->apic_state) {
             device_reset(cpu->apic_state);
         }
+
+        if (boot_info.protected_mode && cpu_is_bsp(cpu)) {
+            reset_cpu(&cpu->env);
+        }
+    }
+
+    if (boot_info.protected_mode) {
+        setup_seg_desc_tables();
+        setup_page_tables();
+        setup_kernel_zero_page();
     }
 }
 
-- 
1.8.3.1