[Xen-devel] [PATCH] x86/boot: Reposition trampoline data

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

... to separate code from data.  In particular, trampoline_realmode_entry's
write to trampoline_cpu_started clobbers the I-cache line containing
trampoline_protmode_entry, which won't be great for AP startup.

Reformat the comments for trampoline_gdt to reduce their volume.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/boot/trampoline.S | 67 ++++++++++++++++++------------------------
 1 file changed, 28 insertions(+), 39 deletions(-)

diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 1761fc1213..1b11b4757a 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -59,45 +59,6 @@ GLOBAL(trampoline_realmode_entry)
         lmsw    %ax                       # CR0.PE = 1 (enter protected mode)
         ljmpl   $BOOT_CS32,$bootsym_rel(trampoline_protmode_entry,6)
 
-trampoline_gdt:
-        /* 0x0000: unused */
-        .quad   0x0000000000000000
-        /* 0x0008: ring 0 code, 32-bit mode */
-        .quad   0x00cf9b000000ffff
-        /* 0x0010: ring 0 code, 64-bit mode */
-        .quad   0x00af9b000000ffff
-        /* 0x0018: ring 0 data */
-        .quad   0x00cf93000000ffff
-        /* 0x0020: real-mode code @ BOOT_TRAMPOLINE */
-        .long   0x0000ffff
-        .long   0x00009b00
-        /* 0x0028: real-mode data @ BOOT_TRAMPOLINE */
-        .long   0x0000ffff
-        .long   0x00009300
-        /*
-         * 0x0030: ring 0 Xen data, 16 MiB size, base
-         * address is computed at runtime.
-         */
-        .quad   0x00c0930000000fff
-.Ltramopline_gdt_end:
-
-        .pushsection .trampoline_rel, "a"
-        .long   trampoline_gdt + BOOT_PSEUDORM_CS + 2 - .
-        .long   trampoline_gdt + BOOT_PSEUDORM_DS + 2 - .
-        .popsection
-
-GLOBAL(trampoline_misc_enable_off)
-        .quad   0
-
-GLOBAL(cpuid_ext_features)
-        .long   0
-
-GLOBAL(trampoline_xen_phys_start)
-        .long   0
-
-GLOBAL(trampoline_cpu_started)
-        .byte   0
-
         .code32
 trampoline_protmode_entry:
         /* Set up a few descriptors: on entry only CS is guaranteed good. */
@@ -186,6 +147,34 @@ idt_48: .word   0, 0, 0 # base = limit = 0
 gdt_48: .word   .Ltramopline_gdt_end - trampoline_gdt - 1
         .long   bootsym_rel(trampoline_gdt,4)
 
+trampoline_gdt:
+        .quad   0x0000000000000000 /* 0x0000: unused */
+        .quad   0x00cf9b000000ffff /* 0x0008: ring 0 code, 32-bit mode */
+        .quad   0x00af9b000000ffff /* 0x0010: ring 0 code, 64-bit mode */
+        .quad   0x00cf93000000ffff /* 0x0018: ring 0 data */
+        .quad   0x00009b000000ffff /* 0x0020: real-mode code @ BOOT_TRAMPOLINE 
*/
+        .quad   0x000093000000ffff /* 0x0028: real-mode data @ BOOT_TRAMPOLINE 
*/
+        .quad   0x00c0930000000fff /* 0x0030: ring 0 Xen data, 16M @ XEN */
+.Ltramopline_gdt_end:
+
+        /* Relocations for trampoline Real Mode segments. */
+        .pushsection .trampoline_rel, "a"
+        .long   trampoline_gdt + BOOT_PSEUDORM_CS + 2 - .
+        .long   trampoline_gdt + BOOT_PSEUDORM_DS + 2 - .
+        .popsection
+
+GLOBAL(trampoline_misc_enable_off)
+        .quad   0
+
+GLOBAL(cpuid_ext_features)
+        .long   0
+
+GLOBAL(trampoline_xen_phys_start)
+        .long   0
+
+GLOBAL(trampoline_cpu_started)
+        .byte   0
+
 /* The first page of trampoline is permanent, the rest boot-time only. */
 /* Reuse the boot trampoline on the 1st trampoline page as stack for wakeup. */
         .equ    wakeup_stack, trampoline_start + PAGE_SIZE
-- 
2.11.0


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