From: Geoff Levand <ge...@infradead.org>
Add the new hcall HVC_CALL_FUNC that allows execution of a
function at EL2.
During CPU reset the CPU must be brought to the exception
level it had on entry to the kernel. The HVC_CALL_FUNC
hcall will provide the mechanism needed for this exception
level switch.
To allow the HVC_CALL_FUNC exception vector to work without
a stack, which is needed to support an hcall at CPU reset,
this implementation uses register x18 to store the link
register across the caller provided function. This dictates
that the caller provided function must preserve the
contents of register x18.
Signed-off-by: Geoff Levand <ge...@infradead.org>
---
arch/arm64/include/asm/virt.h | 13 +++++++++++++
arch/arm64/kernel/hyp-stub.S | 13 ++++++++++++-
2 files changed, 25 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index eb10368..3070096 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -45,6 +45,19 @@
#define HVC_SET_VECTORS 2
+/*
+ * HVC_CALL_FUNC - Execute a function at EL2.
+ *
+ * @x0: Physical address of the function to be executed.
+ * @x1: Passed as the first argument to the function.
+ * @x2: Passed as the second argument to the function.
+ * @x3: Passed as the third argument to the function.
+ *
+ * The called function must preserve the contents of register x18.
+ */
+
+#define HVC_CALL_FUNC 3
+
#define BOOT_CPU_MODE_EL1 (0xe11)
#define BOOT_CPU_MODE_EL2 (0xe12)
diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 017ab519..e8febe9 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -67,8 +67,19 @@ el1_sync:
b 2f
1: cmp x18, #HVC_SET_VECTORS
- b.ne 2f
+ b.ne 1f
msr vbar_el2, x0
+ b 2f
+
+1: cmp x18, #HVC_CALL_FUNC
+ b.ne 2f
+ mov x18, lr
+ mov lr, x0
+ mov x0, x1
+ mov x1, x2
+ mov x2, x3
+ blr lr
+ mov lr, x18
2: eret
ENDPROC(el1_sync)
--
2.7.4
--
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