plat/kvm/arm: Obsolete `EL0` logic from trap/IRQ handling

Although the Vector table has `EL0` exceptions related entries,
we never execute from `EL0` and they will never happen.

Furthermore, `SP_EL0` is a perfect candidate for an emergency
scratch register in an `EL1` only OS like us.

Thus, remove all of the `EL0` logic, while maintaining the same
alignments and semantics.

Signed-off-by: Sergiu Moga <sergiu@unikraft.io>

diff --git a/arch/arm/arm64/include/uk/asm/lcpu.h b/arch/arm/arm64/include/uk/asm/lcpu.h
index c8b28669c756e298cc3126837d66a6ffff73bcd5..4a4ad1581941402ec8816fb21e952adbef602296 100644 (file)
--- a/arch/arm/arm64/include/uk/asm/lcpu.h
+++ b/arch/arm/arm64/include/uk/asm/lcpu.h
@@ -170,16 +170,14 @@ unsigned char tcr_ips_bits[] = {32, 36, 40, 42, 44, 48, 52};
 /*
  * Stack size to save general purpose registers and essential system
  * registers. 8 * (30 + lr + elr_el1 + spsr_el1 + esr_el1) = 272.
- * From exceptions come from EL0, we have to save sp_el0. So the
- * TRAP_STACK_SIZE should be 272 + 8 = 280. But we enable the stack
- * alignment check, we will force align the stack for EL1 exceptions,
- * so we add a sp to save original stack pointer: 280 + 8 = 288
+ * We enable the stack alignment check, we will force align the stack for
+ * EL1 exceptions, so we add a sp to save original stack pointer: 272 + 8 = 280
+ * and then a padding of 8 bytes: 280 + 8 = 288 (288 % 16 == 0).
  *
  * TODO: We'd better to calculate this size automatically later.
  */
 #define __TRAP_STACK_SIZE      288
 #define __SP_OFFSET            272
-#define __SP_EL0_OFFSET                280
 
 /*
  * In thread context switch, we will save the callee-saved registers
@@ -216,8 +214,8 @@ struct __regs {
        /* Stack Pointer */
        uint64_t sp;
 
-       /* Stack Pointer from el0 */
-       uint64_t sp_el0;
+       /* Padding to make sure this structure is 16-byte aligned */
+       __u8 pad[8];
 };
 
 /*

diff --git a/plat/kvm/arm/exceptions.S b/plat/kvm/arm/exceptions.S
index 5815cba02e9821f980643f628acf141b08a81ef6..98501c13b417853411ef0e94f0d4f1bd3c36a487 100644 (file)
--- a/plat/kvm/arm/exceptions.S
+++ b/plat/kvm/arm/exceptions.S
@@ -66,14 +66,9 @@
        EXCHANGE_SP_WITH_X0
 .endm
 
-.macro ENTER_TRAP, el
+.macro SAVE_REGS
        sub sp, sp, #__TRAP_STACK_SIZE
 
-.if    \el != 0
-       /* Force align the stack, and save SP to __SP_OFFSET */
-       ALIGN_STACK
-.endif
-
        /* Save general purpose registers */
        stp x0, x1, [sp, #16 * 0]
        stp x2, x3, [sp, #16 * 1]
@@ -99,16 +94,9 @@
        mrs x22, spsr_el1
        mrs x23, esr_el1
        stp x22, x23, [sp, #16 * 16]
-
-.if \el == 0
-       /* Save stack pointer for lower level exception */
-       mrs x18, sp_el0
-       str x18, [sp, #__SP_EL0_OFFSET]
-.endif
-
 .endm
 
-.macro LEAVE_TRAP, el
+.macro RESTORE_REGS
        /* Mask IRQ to make sure restore would not be interrupted by IRQ */
        msr daifset, #2
 
@@ -138,14 +126,6 @@
        ldp x2, x3, [sp, #16 * 1]
        ldp x0, x1, [sp, #16 * 0]
 
-.if \el == 0
-       /* Restore stack pointer for exception from EL0 */
-       ldr x18, [sp, #__SP_EL0_OFFSET]
-       msr sp_el0, x18
-
-       /* Restore x18, x19 */
-       ldp x18, x19, [sp, #16 * 9]
-.else
        /* Restore stack pointer for exception from EL1 */
        ldr x18, [sp, #__SP_OFFSET]
        mov x19, sp
@@ -153,7 +133,7 @@
 
        /* Restore x18, x19 */
        ldp x18, x19, [x19, #16 * 9]
-.endif
+
        add sp, sp, #__TRAP_STACK_SIZE
 
        eret
@@ -166,19 +146,19 @@
  */
 .align 6
 el1_sync:
-       ENTER_TRAP 1
+       SAVE_REGS
        mov x0, sp
        mrs x1, far_el1
        bl trap_el1_sync
-       LEAVE_TRAP 1
+       RESTORE_REGS
 
 .align 6
 el1_irq:
-       ENTER_TRAP 1
+       SAVE_REGS
        msr daifclr, #(8 | 4 | 1)
        mov x0, sp
        bl trap_el1_irq
-       LEAVE_TRAP 1
+       RESTORE_REGS
 
 /* Bad Abort numbers */
 #define BAD_SYNC  0
@@ -189,7 +169,7 @@ el1_irq:
 #define el_invalid(name, reason, el)   \
 .align 6;                              \
 name##_invalid:                                \
-       ENTER_TRAP  el;                 \
+       SAVE_REGS;                      \
        mov x0, sp;                     \
        mov x1, el;                     \
        mov x2, #(reason);              \