KVM: arm64: Make indirect vectors preamble behaviour symmetric

The KVM indirect vectors support is a little complicated. Different CPUs
may use different exception vectors for KVM that are generated at boot.
Adding new instructions involves checking all the possible combinations
do the right thing.

To make changes here easier to review lets state what we expect of the
preamble:
  1. The first vector run, must always run the preamble.
  2. Patching the head or tail of the vector shouldn't remove
     preamble instructions.

Today, this is easy as we only have one instruction in the preamble.
Change the unpatched tail of the indirect vector so that it always
runs this, regardless of patching.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index 318a2f3..a911b8f 100644 (file)
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -275,7 +275,7 @@ ENDPROC(__kvm_hyp_vector)
 /*
  * The default sequence is to directly branch to the KVM vectors,
  * using the computed offset. This applies for VHE as well as
- * !ARM64_HARDEN_EL2_VECTORS.
+ * !ARM64_HARDEN_EL2_VECTORS. The first vector must always run the preamble.
  *
  * For ARM64_HARDEN_EL2_VECTORS configurations, this gets replaced
  * with:
@@ -291,8 +291,8 @@ ENDPROC(__kvm_hyp_vector)
  * See kvm_patch_vector_branch for details.
  */
 alternative_cb kvm_patch_vector_branch
-       b       __kvm_hyp_vector + (1b - 0b)
-       nop
+       stp     x0, x1, [sp, #-16]!
+       b       __kvm_hyp_vector + (1b - 0b + KVM_VECTOR_PREAMBLE)
        nop
        nop
        nop