arm64: KVM: Only force FPEXC32_EL2.EN if trapping FPSIMD

If trapping FPSIMD in the context of an AArch32 guest, it is critical
to set FPEXC32_EL2.EN to 1 so that the trapping is taken to EL2 and
not EL1.

Conversely, it is just as critical *not* to set FPEXC32_EL2.EN to 1
if we're not going to trap FPSIMD, as we then corrupt the existing
VFP state.

Moving the call to __activate_traps_fpsimd32 to the point where we
know for sure that we are going to trap ensures that we don't set that
bit spuriously.

Fixes: e6b673b741ea ("KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing")
Cc: stable@vger.kernel.org # v4.18
Cc: Dave Martin <dave.martin@arm.com>
Reported-by: Alexander Graf <agraf@suse.de>
Tested-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>

diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index d496ef5..ca46153 100644 (file)
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -98,8 +98,10 @@ static void activate_traps_vhe(struct kvm_vcpu *vcpu)
        val = read_sysreg(cpacr_el1);
        val |= CPACR_EL1_TTA;
        val &= ~CPACR_EL1_ZEN;
-       if (!update_fp_enabled(vcpu))
+       if (!update_fp_enabled(vcpu)) {
                val &= ~CPACR_EL1_FPEN;
+               __activate_traps_fpsimd32(vcpu);
+       }
 
        write_sysreg(val, cpacr_el1);
 
@@ -114,8 +116,10 @@ static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)
 
        val = CPTR_EL2_DEFAULT;
        val |= CPTR_EL2_TTA | CPTR_EL2_TZ;
-       if (!update_fp_enabled(vcpu))
+       if (!update_fp_enabled(vcpu)) {
                val |= CPTR_EL2_TFP;
+               __activate_traps_fpsimd32(vcpu);
+       }
 
        write_sysreg(val, cptr_el2);
 }
@@ -129,7 +133,6 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
        if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN) && (hcr & HCR_VSE))
                write_sysreg_s(vcpu->arch.vsesr_el2, SYS_VSESR_EL2);
 
-       __activate_traps_fpsimd32(vcpu);
        if (has_vhe())
                activate_traps_vhe(vcpu);
        else