[PATCH v1 6/7] KVM: arm64: Eagerly restore host fpsimd/sve state in pKVM
Fuad Tabba
tabba at google.com
Fri May 17 06:18:13 PDT 2024
When running in protected mode we don't want to leak protected
guest state to the host, including whether a guest has used
fpsimd/sve. Therefore, eagerly restore the host state on guest
exit when running in protected mode, which happens only if the
guest has used fpsimd/sve.
As a future optimisation, we could go back to lazy restoring
state at the host after exiting non-protected guests.
Signed-off-by: Fuad Tabba <tabba at google.com>
---
arch/arm64/kvm/hyp/include/hyp/switch.h | 10 +++++
arch/arm64/kvm/hyp/nvhe/hyp-main.c | 57 +++++++++++++++++++++++--
arch/arm64/kvm/hyp/nvhe/pkvm.c | 2 +
arch/arm64/kvm/hyp/nvhe/switch.c | 18 +++++++-
4 files changed, 82 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index d15272445db2..4dc620499e5d 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -320,6 +320,16 @@ static inline void __hyp_sve_restore_guest(struct kvm_vcpu *vcpu)
write_sysreg_el1(__vcpu_sys_reg(vcpu, ZCR_EL1), SYS_ZCR);
}
+static inline void __hyp_sve_save_host(void)
+{
+ struct user_sve_state *sve_state = *host_data_ptr(sve_state);
+
+ sve_state->zcr_el1 = read_sysreg_el1(SYS_ZCR);
+ sve_cond_update_zcr_vq(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
+ __sve_save_state(sve_state->sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
+ &sve_state->fpsr);
+}
+
static void __deactivate_fpsimd_sve_traps(struct kvm_vcpu *vcpu);
static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu);
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index d5c48dc98f67..8b9556f5dee3 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -23,20 +23,70 @@ DEFINE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
void __kvm_hyp_host_forward_smc(struct kvm_cpu_context *host_ctxt);
+static void __hyp_sve_save_guest(struct kvm_vcpu *vcpu)
+{
+ __vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
+ sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1, SYS_ZCR_EL2);
+ __sve_save_state(vcpu_sve_pffr(vcpu), &vcpu->arch.ctxt.fp_regs.fpsr);
+ sve_cond_update_zcr_vq(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
+}
+
+static void __hyp_sve_restore_host(void)
+{
+ struct user_sve_state *sve_state = *host_data_ptr(sve_state);
+
+ sve_cond_update_zcr_vq(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
+ __sve_restore_state(sve_state->sve_regs + sve_ffr_offset(kvm_host_sve_max_vl),
+ &sve_state->fpsr);
+ write_sysreg_el1(sve_state->zcr_el1, SYS_ZCR);
+}
+
+static void fpsimd_sve_flush(void)
+{
+ *host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
+}
+
+static void fpsimd_sve_sync(struct kvm_vcpu *vcpu)
+{
+ if (!guest_owns_fp_regs())
+ return;
+
+ if (has_hvhe())
+ sysreg_clear_set(cpacr_el1, 0,
+ (CPACR_EL1_ZEN_EL1EN | CPACR_EL1_ZEN_EL0EN |
+ CPACR_EL1_FPEN_EL1EN | CPACR_EL1_FPEN_EL0EN));
+ else
+ sysreg_clear_set(cptr_el2, CPTR_EL2_TZ | CPTR_EL2_TFP, 0);
+ isb();
+
+ if (vcpu_has_sve(vcpu))
+ __hyp_sve_save_guest(vcpu);
+ else
+ __fpsimd_save_state(&vcpu->arch.ctxt.fp_regs);
+
+ if (system_supports_sve())
+ __hyp_sve_restore_host();
+ else
+ __fpsimd_restore_state(*host_data_ptr(fpsimd_state));
+
+ *host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
+}
+
static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
{
struct kvm_vcpu *host_vcpu = hyp_vcpu->host_vcpu;
+ fpsimd_sve_flush();
+
hyp_vcpu->vcpu.arch.ctxt = host_vcpu->arch.ctxt;
hyp_vcpu->vcpu.arch.sve_state = kern_hyp_va(host_vcpu->arch.sve_state);
- hyp_vcpu->vcpu.arch.sve_max_vl = host_vcpu->arch.sve_max_vl;
+ hyp_vcpu->vcpu.arch.sve_max_vl = min(host_vcpu->arch.sve_max_vl, kvm_host_sve_max_vl);
hyp_vcpu->vcpu.arch.hw_mmu = host_vcpu->arch.hw_mmu;
hyp_vcpu->vcpu.arch.hcr_el2 = host_vcpu->arch.hcr_el2;
hyp_vcpu->vcpu.arch.mdcr_el2 = host_vcpu->arch.mdcr_el2;
- hyp_vcpu->vcpu.arch.cptr_el2 = host_vcpu->arch.cptr_el2;
hyp_vcpu->vcpu.arch.iflags = host_vcpu->arch.iflags;
@@ -54,10 +104,11 @@ static void sync_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
struct vgic_v3_cpu_if *host_cpu_if = &host_vcpu->arch.vgic_cpu.vgic_v3;
unsigned int i;
+ fpsimd_sve_sync(&hyp_vcpu->vcpu);
+
host_vcpu->arch.ctxt = hyp_vcpu->vcpu.arch.ctxt;
host_vcpu->arch.hcr_el2 = hyp_vcpu->vcpu.arch.hcr_el2;
- host_vcpu->arch.cptr_el2 = hyp_vcpu->vcpu.arch.cptr_el2;
host_vcpu->arch.fault = hyp_vcpu->vcpu.arch.fault;
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 25e9a94f6d76..feb27b4ce459 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -588,6 +588,8 @@ int __pkvm_init_vcpu(pkvm_handle_t handle, struct kvm_vcpu *host_vcpu,
if (ret)
unmap_donated_memory(hyp_vcpu, sizeof(*hyp_vcpu));
+ hyp_vcpu->vcpu.arch.cptr_el2 = kvm_get_reset_cptr_el2(&hyp_vcpu->vcpu);
+
return ret;
}
diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
index 935f3db245e9..a2e1419f0f0f 100644
--- a/arch/arm64/kvm/hyp/nvhe/switch.c
+++ b/arch/arm64/kvm/hyp/nvhe/switch.c
@@ -114,7 +114,8 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
static void __deactivate_fpsimd_sve_traps(struct kvm_vcpu *vcpu)
{
- bool clear_sve_traps = vcpu_has_sve(vcpu);
+ bool clear_sve_traps = vcpu_has_sve(vcpu) ||
+ (is_protected_kvm_enabled() && system_supports_sve());
u64 reg;
if (has_hvhe()) {
@@ -205,7 +206,20 @@ static bool kvm_handle_pvm_sys64(struct kvm_vcpu *vcpu, u64 *exit_code)
static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
{
- __fpsimd_save_state(*host_data_ptr(fpsimd_state));
+ /*
+ * Non-protected kvm relies on the host restoring its sve state.
+ * Protected kvm restores the host's sve state as not to reveal that
+ * fpsimd was used by a guest nor leak upper sve bits.
+ */
+ if (unlikely(is_protected_kvm_enabled() && system_supports_sve())) {
+ __hyp_sve_save_host();
+
+ /* Re-enable SVE traps for guests that do not support it. */
+ if (!vcpu_has_sve(vcpu))
+ sysreg_clear_set(cptr_el2, 0, CPTR_EL2_TZ);
+ } else {
+ __fpsimd_save_state(*host_data_ptr(fpsimd_state));
+ }
}
static const exit_handler_fn hyp_exit_handlers[] = {
--
2.45.0.rc1.225.g2a3ae87e7f-goog
More information about the linux-arm-kernel
mailing list