[PATCH v2 2/4] KVM: arm64: Optimise away S1POE handling when not supported by host

[Fuad Tabba]

Although ID register sanitisation prevents guests from seeing the
feature, adding this check to the helper allows the compiler to entirely
eliminate S1POE-specific code paths (such as context switching POR_EL1)
when the host kernel is compiled without support (CONFIG_ARM64_POE is
disabled).

This aligns with the pattern used for other optional features like SVE
(kvm_has_sve()) and FPMR (kvm_has_fpmr()), ensuring no POE logic if the
host lacks support, regardless of the guest configuration state.

Signed-off-by: Fuad Tabba <tabba at google.com>
---
 arch/arm64/include/asm/kvm_host.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index ac7f970c7883..7af72ca749a6 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -1592,7 +1592,8 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
 	(kvm_has_feat((k), ID_AA64MMFR3_EL1, S1PIE, IMP))
 
 #define kvm_has_s1poe(k)				\
-	(kvm_has_feat((k), ID_AA64MMFR3_EL1, S1POE, IMP))
+	(system_supports_poe() &&			\
+	 kvm_has_feat((k), ID_AA64MMFR3_EL1, S1POE, IMP))
 
 #define kvm_has_ras(k)					\
 	(kvm_has_feat((k), ID_AA64PFR0_EL1, RAS, IMP))
-- 
2.53.0.273.g2a3d683680-goog