The hyp code FPSIMD/SVE/SME trap handling logic has some rather messy open-coded manipulation of CPTR/CPACR. This is benign for non-nested guests, but broken for nested guests, as the guest hypervisor's CPTR configuration is not taken into account.
Consider the case where L0 provides FPSIMD+SVE to an L1 guest hypervisor, and the L1 guest hypervisor only provides FPSIMD to an L2 guest (with L1 configuring CPTR/CPACR to trap SVE usage from L2). If the L2 guest triggers an FPSIMD trap to the L0 hypervisor, kvm_hyp_handle_fpsimd() will see that the vCPU supports FPSIMD+SVE, and will configure CPTR/CPACR to NOT trap FPSIMD+SVE before returning to the L2 guest. Consequently the L2 guest would be able to manipulate SVE state even though the L1 hypervisor had configured CPTR/CPACR to forbid this.
Clean this up, and fix the nested virt issue by always using __deactivate_cptr_traps() and __activate_cptr_traps() to manage the CPTR traps. This removes the need for the ad-hoc fixup in kvm_hyp_save_fpsimd_host(), and ensures that any guest hypervisor configuration of CPTR/CPACR is taken into account.
Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: Fuad Tabba tabba@google.com Cc: Marc Zyngier maz@kernel.org Cc: Mark Brown broonie@kernel.org Cc: Oliver Upton oliver.upton@linux.dev Cc: Will Deacon will@kernel.org --- arch/arm64/kvm/hyp/include/hyp/switch.h | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-)
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h index 9b025276fcc8e..ce001a2b6421c 100644 --- a/arch/arm64/kvm/hyp/include/hyp/switch.h +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h @@ -617,11 +617,6 @@ static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu) */ if (system_supports_sve()) { __hyp_sve_save_host(); - - /* Re-enable SVE traps if not supported for the guest vcpu. */ - if (!vcpu_has_sve(vcpu)) - cpacr_clear_set(CPACR_EL1_ZEN, 0); - } else { __fpsimd_save_state(host_data_ptr(host_ctxt.fp_regs)); } @@ -672,10 +667,7 @@ static inline bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code) /* Valid trap. Switch the context: */
/* First disable enough traps to allow us to update the registers */ - if (sve_guest || (is_protected_kvm_enabled() && system_supports_sve())) - cpacr_clear_set(0, CPACR_EL1_FPEN | CPACR_EL1_ZEN); - else - cpacr_clear_set(0, CPACR_EL1_FPEN); + __deactivate_cptr_traps(vcpu); isb();
/* Write out the host state if it's in the registers */ @@ -697,6 +689,13 @@ static inline bool kvm_hyp_handle_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
*host_data_ptr(fp_owner) = FP_STATE_GUEST_OWNED;
+ /* + * Re-enable traps necessary for the current state of the guest, e.g. + * those enabled by a guest hypervisor. The ERET to the guest will + * provide the necessary context synchronization. + */ + __activate_cptr_traps(vcpu); + return true; }