[Minios-devel] [UNIKRAFT PATCH 2/4] plat/kvm: remove 32-bit GDT entry

[Florian Schmidt <florian.schmidt@xxxxxxxxx>]

Since we spend almost no time in 32-bit mode, and never do any calls or
returns, there's no reason to have a specific section in the GDT for
32-bit code. Just set up the bare essentials, then move on to long mode.

Signed-off-by: Florian Schmidt <florian.schmidt@xxxxxxxxx>
---
 plat/kvm/include/kvm-x86/traps.h |  9 ++++-----
 plat/kvm/x86/entry64.S           | 14 +++-----------
 2 files changed, 7 insertions(+), 16 deletions(-)

diff --git a/plat/kvm/include/kvm-x86/traps.h b/plat/kvm/include/kvm-x86/traps.h
index c457bda5..39bf0386 100644
--- a/plat/kvm/include/kvm-x86/traps.h
+++ b/plat/kvm/include/kvm-x86/traps.h
@@ -29,14 +29,13 @@
  */
 #define GDT_DESC_NULL           0
 #define GDT_DESC_CODE           1
-#define GDT_DESC_CODE32         2 /* Used by _libkvmplat_start32 */
-#define GDT_DESC_DATA           3
-#define GDT_DESC_TSS_LO         4
-#define GDT_DESC_TSS_HI         5
+#define GDT_DESC_DATA           2
+#define GDT_DESC_TSS_LO         3
+#define GDT_DESC_TSS_HI         4
 #define GDT_DESC_TSS            GDT_DESC_TSS_LO
 
 #define GDT_DESC_OFFSET(n)      ((n) * 0x8)
-#define GDT_NUM_ENTRIES         6
+#define GDT_NUM_ENTRIES         5
 
 #define GDT_DESC_CODE_VAL       0x00af99000000ffff
 #define GDT_DESC_CODE32_VAL     0x00cf9b000000ffff
diff --git a/plat/kvm/x86/entry64.S b/plat/kvm/x86/entry64.S
index e15d41e2..7647446d 100644
--- a/plat/kvm/x86/entry64.S
+++ b/plat/kvm/x86/entry64.S
@@ -79,14 +79,8 @@ ENTRY(_libkvmplat_start32)
        jne nomultiboot
 
        lgdt (gdt64_ptr)
-       /* let lret jump just one instruction ahead, but set %cs
-        * to the correct GDT entry while doing that.
-        */
-       pushl $(gdt64_32cs-gdt64)
-       pushl $1f
-       lret
 
-1:     movl $(gdt64_ds-gdt64), %eax
+       movl $(gdt64_ds-gdt64), %eax
        movl %eax, %ds
        movl %eax, %es
        movl %eax, %ss
@@ -122,7 +116,7 @@ ENTRY(_libkvmplat_start32)
        /* 5: poetically longjump to longmode,
         *    letting lret set %cs to the correct GDT entry on the way
         */
-       pushl $(gdt64_64cs-gdt64)
+       pushl $(gdt64_cs-gdt64)
        pushl $_libkvmplat_start64
        lret
 
@@ -149,10 +143,8 @@ END(_libkvmplat_start32)
 .align 64
 gdt64:
        .quad 0x0000000000000000
-gdt64_64cs:
+gdt64_cs:
        .quad GDT_DESC_CODE_VAL         /* 64bit CS             */
-gdt64_32cs:
-       .quad GDT_DESC_CODE32_VAL       /* 32bit CS             */
 gdt64_ds:
        .quad GDT_DESC_DATA_VAL         /* DS                   */
        .quad 0x0000000000000000        /* TSS part 1 (via C)   */
-- 
2.21.0


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