[RFC PATCH 30/73] KVM: x86/PVM: Implement segment related callbacks

Lai Jiangshan
2024-02-26T14:36:16Z

Segmentation in PVM guest is generally disabled and is only available
for instruction emulation. The segment descriptors of segment registers
are just cached and do not take effect in hardware. Since the PVM guest
is only allowed to run in x86 long mode, the value of guest CS/SS is
fixed and depends on the current mode.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
arch/x86/kvm/pvm/pvm.c | 128 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 128 insertions(+)

diff --git a/arch/x86/kvm/pvm/pvm.c b/arch/x86/kvm/pvm/pvm.c
index 26b2201f7dde..6f91dffb6c50 100644
--- a/arch/x86/kvm/pvm/pvm.c
+++ b/arch/x86/kvm/pvm/pvm.c
@@ -630,6 +630,52 @@ static int pvm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return ret;
}

+static void pvm_get_segment(struct kvm_vcpu *vcpu,
+ struct kvm_segment *var, int seg)
+{
+ struct vcpu_pvm *pvm = to_pvm(vcpu);
+
+ // Update CS or SS to reflect the current mode.
+ if (seg == VCPU_SREG_CS) {
+ if (is_smod(pvm)) {
+ pvm->segments[seg].selector = kernel_cs_by_msr(pvm->msr_star);
+ pvm->segments[seg].dpl = 0;
+ pvm->segments[seg].l = 1;
+ pvm->segments[seg].db = 0;
+ } else {
+ pvm->segments[seg].selector = pvm->hw_cs >> 3;
+ pvm->segments[seg].dpl = 3;
+ if (pvm->hw_cs == __USER_CS) {
+ pvm->segments[seg].l = 1;
+ pvm->segments[seg].db = 0;
+ } else { // __USER32_CS
+ pvm->segments[seg].l = 0;
+ pvm->segments[seg].db = 1;
+ }
+ }
+ } else if (seg == VCPU_SREG_SS) {
+ if (is_smod(pvm)) {
+ pvm->segments[seg].dpl = 0;
+ pvm->segments[seg].selector = kernel_ds_by_msr(pvm->msr_star);
+ } else {
+ pvm->segments[seg].dpl = 3;
+ pvm->segments[seg].selector = pvm->hw_ss >> 3;
+ }
+ }
+
+ // Update DS/ES/FS/GS states from the hardware when the states are loaded.
+ pvm_switch_to_host(pvm);
+ *var = pvm->segments[seg];
+}
+
+static u64 pvm_get_segment_base(struct kvm_vcpu *vcpu, int seg)
+{
+ struct kvm_segment var;
+
+ pvm_get_segment(vcpu, &var, seg);
+ return var.base;
+}
+
static int pvm_get_cpl(struct kvm_vcpu *vcpu)
{
if (is_smod(to_pvm(vcpu)))
@@ -637,6 +683,80 @@ static int pvm_get_cpl(struct kvm_vcpu *vcpu)
return 3;
}

+static void pvm_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
+{
+ struct vcpu_pvm *pvm = to_pvm(vcpu);
+ int cpl = pvm_get_cpl(vcpu);
+
+ // Unload DS/ES/FS/GS states from hardware before changing them.
+ // It also has to unload the VCPU when leaving PVM mode.
+ pvm_switch_to_host(pvm);
+ pvm->segments[seg] = *var;
+
+ switch (seg) {
+ case VCPU_SREG_CS:
+ if (var->dpl == 1 || var->dpl == 2)
+ goto invalid_change;
+ if (!kvm_vcpu_has_run(vcpu)) {
+ // CPL changing is only valid for the first changed
+ // after the vcpu is created (vm-migration).
+ if (cpl != var->dpl)
+ pvm_switch_flags_toggle_mod(pvm);
+ } else {
+ if (cpl != var->dpl)
+ goto invalid_change;
+ if (cpl == 0 && !var->l)
+ goto invalid_change;
+ }
+ break;
+ case VCPU_SREG_LDTR:
+ // pvm doesn't support LDT
+ if (var->selector)
+ goto invalid_change;
+ break;
+ default:
+ break;
+ }
+
+ return;
+
+invalid_change:
+ kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
+}
+
+static void pvm_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l)
+{
+ struct vcpu_pvm *pvm = to_pvm(vcpu);
+
+ if (pvm->hw_cs == __USER_CS) {
+ *db = 0;
+ *l = 1;
+ } else {
+ *db = 1;
+ *l = 0;
+ }
+}
+
+static void pvm_get_idt(struct kvm_vcpu *vcpu, struct desc_ptr *dt)
+{
+ *dt = to_pvm(vcpu)->idt_ptr;
+}
+
+static void pvm_set_idt(struct kvm_vcpu *vcpu, struct desc_ptr *dt)
+{
+ to_pvm(vcpu)->idt_ptr = *dt;
+}
+
+static void pvm_get_gdt(struct kvm_vcpu *vcpu, struct desc_ptr *dt)
+{
+ *dt = to_pvm(vcpu)->gdt_ptr;
+}
+
+static void pvm_set_gdt(struct kvm_vcpu *vcpu, struct desc_ptr *dt)
+{
+ to_pvm(vcpu)->gdt_ptr = *dt;
+}
+
static void pvm_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
int trig_mode, int vector)
{
@@ -1545,8 +1665,16 @@ static struct kvm_x86_ops pvm_x86_ops __initdata = {
.get_msr_feature = pvm_get_msr_feature,
.get_msr = pvm_get_msr,
.set_msr = pvm_set_msr,
+ .get_segment_base = pvm_get_segment_base,
+ .get_segment = pvm_get_segment,
+ .set_segment = pvm_set_segment,
.get_cpl = pvm_get_cpl,
+ .get_cs_db_l_bits = pvm_get_cs_db_l_bits,
.load_mmu_pgd = pvm_load_mmu_pgd,
+ .get_gdt = pvm_get_gdt,
+ .set_gdt = pvm_set_gdt,
+ .get_idt = pvm_get_idt,
+ .set_idt = pvm_set_idt,
.get_rflags = pvm_get_rflags,
.set_rflags = pvm_set_rflags,
.get_if_flag = pvm_get_if_flag,
--
2.19.1.6.gb485710b