[PATCH v5 09/19] KVM:x86: Make guest supervisor states as non-XSAVE managed

Yang Weijiang
2023-08-03T07:37:36Z

Save guest CET supervisor states, i.e.,PL{0,1,2}_SSP, when vCPU
is exiting to userspace or being preempted. Reload the MSRs
before vm-entry.

Embeded the helpers in {vmx,svm}_prepare_switch_to_guest() and
vmx_prepare_switch_to_host()/svm_prepare_host_switch() to employ
existing guest state management and optimize the invocation of
the helpers.

Enabling CET supervisor state management in KVM due to:
-Introducing unnecessary XSAVE operation when switch to non-vCPU
userspace within current FPU framework.
-Forcing allocating additional space for CET supervisor states in
each thread context regardless whether it's vCPU thread or not.

Suggested-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/cpuid.h | 11 +++++++++++
arch/x86/kvm/svm/svm.c | 2 ++
arch/x86/kvm/vmx/vmx.c | 2 ++
arch/x86/kvm/x86.c | 27 +++++++++++++++++++++++++++
arch/x86/kvm/x86.h | 3 +++
6 files changed, 46 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 20bbcd95511f..69cbc9d9b277 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -805,6 +805,7 @@ struct kvm_vcpu_arch {
u64 xcr0;
u64 guest_supported_xcr0;
u64 guest_supported_xss;
+ u64 cet_s_ssp[3];

struct kvm_pio_request pio;
void *pio_data;
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index b1658c0de847..b221a663de4c 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -232,4 +232,15 @@ static __always_inline bool guest_pv_has(struct kvm_vcpu *vcpu,
return vcpu->arch.pv_cpuid.features & (1u << kvm_feature);
}

+/*
+ * FIXME: When the "KVM-governed" enabling patchset is merge, rebase this
+ * series on top of that and add a new patch for CET to replace this helper
+ * with the qualified one.
+ */
+static __always_inline bool guest_can_use(struct kvm_vcpu *vcpu,
+ unsigned int feature)
+{
+ return kvm_cpu_cap_has(feature) && guest_cpuid_has(vcpu, feature);
+}
+
#endif
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 1bc0936bbd51..8652e86fbfb2 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1515,11 +1515,13 @@ static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
if (likely(tsc_aux_uret_slot >= 0))
kvm_set_user_return_msr(tsc_aux_uret_slot, svm->tsc_aux, -1ull);

+ reload_cet_supervisor_ssp(vcpu);
svm->guest_state_loaded = true;
}

static void svm_prepare_host_switch(struct kvm_vcpu *vcpu)
{
+ save_cet_supervisor_ssp(vcpu);
to_svm(vcpu)->guest_state_loaded = false;
}

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c8d9870cfecb..6aa76124e81e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1323,6 +1323,7 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
gs_base = segment_base(gs_sel);
#endif

+ reload_cet_supervisor_ssp(vcpu);
vmx_set_host_fs_gs(host_state, fs_sel, gs_sel, fs_base, gs_base);
vmx->guest_state_loaded = true;
}
@@ -1362,6 +1363,7 @@ static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx)
wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
#endif
load_fixmap_gdt(raw_smp_processor_id());
+ save_cet_supervisor_ssp(&vmx->vcpu);
vmx->guest_state_loaded = false;
vmx->guest_uret_msrs_loaded = false;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d68ef87fe007..5b63441fd2d2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11128,6 +11128,31 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
trace_kvm_fpu(0);
}

+void save_cet_supervisor_ssp(struct kvm_vcpu *vcpu)
+{
+ if (unlikely(guest_can_use(vcpu, X86_FEATURE_SHSTK))) {
+ rdmsrl(MSR_IA32_PL0_SSP, vcpu->arch.cet_s_ssp[0]);
+ rdmsrl(MSR_IA32_PL1_SSP, vcpu->arch.cet_s_ssp[1]);
+ rdmsrl(MSR_IA32_PL2_SSP, vcpu->arch.cet_s_ssp[2]);
+ /*
+ * Omit reset to host PL{1,2}_SSP because Linux will never use
+ * these MSRs.
+ */
+ wrmsrl(MSR_IA32_PL0_SSP, 0);
+ }
+}
+EXPORT_SYMBOL_GPL(save_cet_supervisor_ssp);
+
+void reload_cet_supervisor_ssp(struct kvm_vcpu *vcpu)
+{
+ if (unlikely(guest_can_use(vcpu, X86_FEATURE_SHSTK))) {
+ wrmsrl(MSR_IA32_PL0_SSP, vcpu->arch.cet_s_ssp[0]);
+ wrmsrl(MSR_IA32_PL1_SSP, vcpu->arch.cet_s_ssp[1]);
+ wrmsrl(MSR_IA32_PL2_SSP, vcpu->arch.cet_s_ssp[2]);
+ }
+}
+EXPORT_SYMBOL_GPL(reload_cet_supervisor_ssp);
+
int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
{
struct kvm_queued_exception *ex = &vcpu->arch.exception;
@@ -12133,6 +12158,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)

vcpu->arch.cr3 = 0;
kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
+ memset(vcpu->arch.cet_s_ssp, 0, sizeof(vcpu->arch.cet_s_ssp));

/*
* CR0.CD/NW are set on RESET, preserved on INIT. Note, some versions
@@ -12313,6 +12339,7 @@ void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
pmu->need_cleanup = true;
kvm_make_request(KVM_REQ_PMU, vcpu);
}
+
static_call(kvm_x86_sched_in)(vcpu, cpu);
}

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 6e6292915f8c..c69fc027f5ec 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -501,6 +501,9 @@ static inline void kvm_machine_check(void)

void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
+void save_cet_supervisor_ssp(struct kvm_vcpu *vcpu);
+void reload_cet_supervisor_ssp(struct kvm_vcpu *vcpu);
+
int kvm_spec_ctrl_test_value(u64 value);
bool __kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
--
2.27.0