KVM: arm64: Add kvm_extable for vaxorcism code

KVM has a one instruction window where it will allow an SError exception
to be consumed by the hypervisor without treating it as a hypervisor bug.
This is used to consume asynchronous external abort that were caused by
the guest.

As we are about to add another location that survives unexpected exceptions,
generalise this code to make it behave like the host's extable.

KVM's version has to be mapped to EL2 to be accessible on nVHE systems.

The SError vaxorcism code is a one instruction window, so has two entries
in the extable. Because the KVM code is copied for VHE and nVHE, we end up
with four entries, half of which correspond with code that isn't mapped.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index fb1a922b31ba..63350f0e3453 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -193,6 +193,21 @@ extern char __smccc_workaround_1_smc[__SMCCC_WORKAROUND_1_SMC_SZ];
 	ldr	\vcpu, [\ctxt, #HOST_CONTEXT_VCPU]
 .endm
 
+/*
+ * KVM extable for unexpected exceptions.
+ * In the same format _asm_extable, but output to a different section so that
+ * it can be mapped to EL2. The KVM version is not sorted. The caller must
+ * ensure:
+ * x18 has the hypervisor value to allow any Shadow-Call-Stack instrumented
+ * code to write to it, and that SPSR_EL2 and ELR_EL2 are restored by the fixup.
+ */
+.macro	_kvm_extable, from, to
+	.pushsection	__kvm_ex_table, "a"
+	.align		3
+	.long		(\from - .), (\to - .)
+	.popsection
+.endm
+
 #endif
 
 #endif /* __ARM_KVM_ASM_H__ */