KVM: arm64: Refactor exit handlers

The hyp exit handling logic is largely shared between VHE and nVHE/hVHE,
with common logic in arch/arm64/kvm/hyp/include/hyp/switch.h. The code
in the header depends on function definitions provided by
arch/arm64/kvm/hyp/vhe/switch.c and arch/arm64/kvm/hyp/nvhe/switch.c
when they include the header.

This is an unusual header dependency, and prevents the use of
arch/arm64/kvm/hyp/include/hyp/switch.h in other files as this would
result in compiler warnings regarding missing definitions, e.g.

| In file included from arch/arm64/kvm/hyp/nvhe/hyp-main.c:8:
| ./arch/arm64/kvm/hyp/include/hyp/switch.h:733:31: warning: 'kvm_get_exit_handler_array' used but never defined
|   733 | static const exit_handler_fn *kvm_get_exit_handler_array(struct kvm_vcpu *vcpu);
|       |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~
| ./arch/arm64/kvm/hyp/include/hyp/switch.h:735:13: warning: 'early_exit_filter' used but never defined
|   735 | static void early_exit_filter(struct kvm_vcpu *vcpu, u64 *exit_code);
|       |             ^~~~~~~~~~~~~~~~~

Refactor the logic such that the header doesn't depend on anything from
the C files. There should be no functional change as a result of this
patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-7-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

3 files changed, 26 insertions, 41 deletions

diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index c5b8a11ac4f5..46df5c2eeaf5 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -679,23 +679,16 @@ static bool kvm_hyp_handle_dabt_low(struct kvm_vcpu *vcpu, u64 *exit_code)
 
 typedef bool (*exit_handler_fn)(struct kvm_vcpu *, u64 *);
 
-static const exit_handler_fn *kvm_get_exit_handler_array(struct kvm_vcpu *vcpu);
-
-static void early_exit_filter(struct kvm_vcpu *vcpu, u64 *exit_code);
-
 /*
  * Allow the hypervisor to handle the exit with an exit handler if it has one.
  *
  * Returns true if the hypervisor handled the exit, and control should go back
  * to the guest, or false if it hasn't.
  */
-static inline bool kvm_hyp_handle_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
+static inline bool kvm_hyp_handle_exit(struct kvm_vcpu *vcpu, u64 *exit_code,
+				       const exit_handler_fn *handlers)
 {
-	const exit_handler_fn *handlers = kvm_get_exit_handler_array(vcpu);
-	exit_handler_fn fn;
-
-	fn = handlers[kvm_vcpu_trap_get_class(vcpu)];
-
+	exit_handler_fn fn = handlers[kvm_vcpu_trap_get_class(vcpu)];
 	if (fn)
 		return fn(vcpu, exit_code);
 
@@ -725,20 +718,9 @@ static inline void synchronize_vcpu_pstate(struct kvm_vcpu *vcpu, u64 *exit_code
  * the guest, false when we should restore the host state and return to the
  * main run loop.
  */
-static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
+static inline bool __fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code,
+				      const exit_handler_fn *handlers)
 {
-	/*
-	 * Save PSTATE early so that we can evaluate the vcpu mode
-	 * early on.
-	 */
-	synchronize_vcpu_pstate(vcpu, exit_code);
-
-	/*
-	 * Check whether we want to repaint the state one way or
-	 * another.
-	 */
-	early_exit_filter(vcpu, exit_code);
-
 	if (ARM_EXCEPTION_CODE(*exit_code) != ARM_EXCEPTION_IRQ)
 		vcpu->arch.fault.esr_el2 = read_sysreg_el2(SYS_ESR);
 
@@ -768,7 +750,7 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
 		goto exit;
 
 	/* Check if there's an exit handler and allow it to handle the exit. */
-	if (kvm_hyp_handle_exit(vcpu, exit_code))
+	if (kvm_hyp_handle_exit(vcpu, exit_code, handlers))
 		goto guest;
 exit:
 	/* Return to the host kernel and handle the exit */
diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
index 5d79f63a4f86..69d7d3b4294a 100644
--- a/arch/arm64/kvm/hyp/nvhe/switch.c
+++ b/arch/arm64/kvm/hyp/nvhe/switch.c
@@ -250,19 +250,21 @@ static const exit_handler_fn *kvm_get_exit_handler_array(struct kvm_vcpu *vcpu)
 	return hyp_exit_handlers;
 }
 
-/*
- * Some guests (e.g., protected VMs) are not be allowed to run in AArch32.
- * The ARMv8 architecture does not give the hypervisor a mechanism to prevent a
- * guest from dropping to AArch32 EL0 if implemented by the CPU. If the
- * hypervisor spots a guest in such a state ensure it is handled, and don't
- * trust the host to spot or fix it.  The check below is based on the one in
- * kvm_arch_vcpu_ioctl_run().
- *
- * Returns false if the guest ran in AArch32 when it shouldn't have, and
- * thus should exit to the host, or true if a the guest run loop can continue.
- */
-static void early_exit_filter(struct kvm_vcpu *vcpu, u64 *exit_code)
+static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
 {
+	const exit_handler_fn *handlers = kvm_get_exit_handler_array(vcpu);
+
+	synchronize_vcpu_pstate(vcpu, exit_code);
+
+	/*
+	 * Some guests (e.g., protected VMs) are not be allowed to run in
+	 * AArch32.  The ARMv8 architecture does not give the hypervisor a
+	 * mechanism to prevent a guest from dropping to AArch32 EL0 if
+	 * implemented by the CPU. If the hypervisor spots a guest in such a
+	 * state ensure it is handled, and don't trust the host to spot or fix
+	 * it.  The check below is based on the one in
+	 * kvm_arch_vcpu_ioctl_run().
+	 */
 	if (unlikely(vcpu_is_protected(vcpu) && vcpu_mode_is_32bit(vcpu))) {
 		/*
 		 * As we have caught the guest red-handed, decide that it isn't
@@ -275,6 +277,8 @@ static void early_exit_filter(struct kvm_vcpu *vcpu, u64 *exit_code)
 		*exit_code &= BIT(ARM_EXIT_WITH_SERROR_BIT);
 		*exit_code |= ARM_EXCEPTION_IL;
 	}
+
+	return __fixup_guest_exit(vcpu, exit_code, handlers);
 }
 
 /* Switch to the guest for legacy non-VHE systems */
diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index 4748b1947ffa..c854d8445889 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -540,13 +540,10 @@ static const exit_handler_fn hyp_exit_handlers[] = {
 	[ESR_ELx_EC_MOPS]		= kvm_hyp_handle_mops,
 };
 
-static const exit_handler_fn *kvm_get_exit_handler_array(struct kvm_vcpu *vcpu)
+static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
 {
-	return hyp_exit_handlers;
-}
+	synchronize_vcpu_pstate(vcpu, exit_code);
 
-static void early_exit_filter(struct kvm_vcpu *vcpu, u64 *exit_code)
-{
 	/*
 	 * If we were in HYP context on entry, adjust the PSTATE view
 	 * so that the usual helpers work correctly.
@@ -566,6 +563,8 @@ static void early_exit_filter(struct kvm_vcpu *vcpu, u64 *exit_code)
 		*vcpu_cpsr(vcpu) &= ~(PSR_MODE_MASK | PSR_MODE32_BIT);
 		*vcpu_cpsr(vcpu) |= mode;
 	}
+
+	return __fixup_guest_exit(vcpu, exit_code, hyp_exit_handlers);
 }
 
 /* Switch to the guest for VHE systems running in EL2 */