[RFC PATCH 23/73] KVM: x86/PVM: Handle event handling related MSR read/write operation

Lai Jiangshan
2024-02-26T14:35:54Z

In the PVM event handling specification, the guest needs to register the
event entry into the associated MSRs before delivering the event.
Therefore, handling them in the get_msr()/set_msr() callbacks is
necessary to prepare for event delivery later. Additionally, the user
mode syscall event still uses the original syscall event entry, but only
MSR_LSTAR is used; other MSRs are ignored.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
---
arch/x86/kvm/pvm/pvm.c | 188 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/pvm/pvm.h | 7 ++
2 files changed, 195 insertions(+)

diff --git a/arch/x86/kvm/pvm/pvm.c b/arch/x86/kvm/pvm/pvm.c
index 29c6d8da7c19..69f8fbbb6176 100644
--- a/arch/x86/kvm/pvm/pvm.c
+++ b/arch/x86/kvm/pvm/pvm.c
@@ -31,6 +31,33 @@ static bool __read_mostly is_intel;

static unsigned long host_idt_base;

+static inline u16 kernel_cs_by_msr(u64 msr_star)
+{
+ // [47..32]
+ // and force rpl=0
+ return ((msr_star >> 32) & ~0x3);
+}
+
+static inline u16 kernel_ds_by_msr(u64 msr_star)
+{
+ // [47..32] + 8
+ // and force rpl=0
+ return ((msr_star >> 32) & ~0x3) + 8;
+}
+
+static inline u16 user_cs32_by_msr(u64 msr_star)
+{
+ // [63..48] is user_cs32 and force rpl=3
+ return ((msr_star >> 48) | 0x3);
+}
+
+static inline u16 user_cs_by_msr(u64 msr_star)
+{
+ // [63..48] is user_cs32, and [63..48] + 16 is user_cs
+ // and force rpl=3
+ return ((msr_star >> 48) | 0x3) + 16;
+}
+
static inline void __save_gs_base(struct vcpu_pvm *pvm)
{
// switcher will do a real hw swapgs, so use hw MSR_KERNEL_GS_BASE
@@ -261,6 +288,161 @@ static void pvm_sched_in(struct kvm_vcpu *vcpu, int cpu)
{
}

+static int pvm_get_msr_feature(struct kvm_msr_entry *msr)
+{
+ return 1;
+}
+
+static void pvm_msr_filter_changed(struct kvm_vcpu *vcpu)
+{
+ /* Accesses to MSRs are emulated in hypervisor, nothing to do here. */
+}
+
+/*
+ * Reads an msr value (of 'msr_index') into 'msr_info'.
+ * Returns 0 on success, non-0 otherwise.
+ * Assumes vcpu_load() was already called.
+ */
+static int pvm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+{
+ struct vcpu_pvm *pvm = to_pvm(vcpu);
+ int ret = 0;
+
+ switch (msr_info->index) {
+ case MSR_STAR:
+ msr_info->data = pvm->msr_star;
+ break;
+ case MSR_LSTAR:
+ msr_info->data = pvm->msr_lstar;
+ break;
+ case MSR_SYSCALL_MASK:
+ msr_info->data = pvm->msr_syscall_mask;
+ break;
+ case MSR_CSTAR:
+ msr_info->data = pvm->unused_MSR_CSTAR;
+ break;
+ /*
+ * Since SYSENTER is not supported for the guest, we return a bad
+ * segment to the emulator when emulating the instruction for #GP.
+ */
+ case MSR_IA32_SYSENTER_CS:
+ msr_info->data = GDT_ENTRY_INVALID_SEG;
+ break;
+ case MSR_IA32_SYSENTER_EIP:
+ msr_info->data = pvm->unused_MSR_IA32_SYSENTER_EIP;
+ break;
+ case MSR_IA32_SYSENTER_ESP:
+ msr_info->data = pvm->unused_MSR_IA32_SYSENTER_ESP;
+ break;
+ case MSR_PVM_VCPU_STRUCT:
+ msr_info->data = pvm->msr_vcpu_struct;
+ break;
+ case MSR_PVM_SUPERVISOR_RSP:
+ msr_info->data = pvm->msr_supervisor_rsp;
+ break;
+ case MSR_PVM_SUPERVISOR_REDZONE:
+ msr_info->data = pvm->msr_supervisor_redzone;
+ break;
+ case MSR_PVM_EVENT_ENTRY:
+ msr_info->data = pvm->msr_event_entry;
+ break;
+ case MSR_PVM_RETU_RIP:
+ msr_info->data = pvm->msr_retu_rip_plus2 - 2;
+ break;
+ case MSR_PVM_RETS_RIP:
+ msr_info->data = pvm->msr_rets_rip_plus2 - 2;
+ break;
+ default:
+ ret = kvm_get_msr_common(vcpu, msr_info);
+ }
+
+ return ret;
+}
+
+/*
+ * Writes msr value into the appropriate "register".
+ * Returns 0 on success, non-0 otherwise.
+ * Assumes vcpu_load() was already called.
+ */
+static int pvm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+{
+ struct vcpu_pvm *pvm = to_pvm(vcpu);
+ int ret = 0;
+ u32 msr_index = msr_info->index;
+ u64 data = msr_info->data;
+
+ switch (msr_index) {
+ case MSR_STAR:
+ /*
+ * Guest KERNEL_CS/DS shouldn't be NULL and guest USER_CS/DS
+ * must be the same as the host USER_CS/DS.
+ */
+ if (!msr_info->host_initiated) {
+ if (!kernel_cs_by_msr(data))
+ return 1;
+ if (user_cs_by_msr(data) != __USER_CS)
+ return 1;
+ }
+ pvm->msr_star = data;
+ break;
+ case MSR_LSTAR:
+ if (is_noncanonical_address(msr_info->data, vcpu))
+ return 1;
+ pvm->msr_lstar = data;
+ break;
+ case MSR_SYSCALL_MASK:
+ pvm->msr_syscall_mask = data;
+ break;
+ case MSR_CSTAR:
+ pvm->unused_MSR_CSTAR = data;
+ break;
+ case MSR_IA32_SYSENTER_CS:
+ pvm->unused_MSR_IA32_SYSENTER_CS = data;
+ break;
+ case MSR_IA32_SYSENTER_EIP:
+ pvm->unused_MSR_IA32_SYSENTER_EIP = data;
+ break;
+ case MSR_IA32_SYSENTER_ESP:
+ pvm->unused_MSR_IA32_SYSENTER_ESP = data;
+ break;
+ case MSR_PVM_VCPU_STRUCT:
+ if (!PAGE_ALIGNED(data))
+ return 1;
+ if (!data)
+ kvm_gpc_deactivate(&pvm->pvcs_gpc);
+ else if (kvm_gpc_activate(&pvm->pvcs_gpc, data, PAGE_SIZE))
+ return 1;
+
+ pvm->msr_vcpu_struct = data;
+ break;
+ case MSR_PVM_SUPERVISOR_RSP:
+ pvm->msr_supervisor_rsp = msr_info->data;
+ break;
+ case MSR_PVM_SUPERVISOR_REDZONE:
+ pvm->msr_supervisor_redzone = msr_info->data;
+ break;
+ case MSR_PVM_EVENT_ENTRY:
+ if (is_noncanonical_address(data, vcpu) ||
+ is_noncanonical_address(data + 256, vcpu) ||
+ is_noncanonical_address(data + 512, vcpu)) {
+ kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
+ return 1;
+ }
+ pvm->msr_event_entry = msr_info->data;
+ break;
+ case MSR_PVM_RETU_RIP:
+ pvm->msr_retu_rip_plus2 = msr_info->data + 2;
+ break;
+ case MSR_PVM_RETS_RIP:
+ pvm->msr_rets_rip_plus2 = msr_info->data + 2;
+ break;
+ default:
+ ret = kvm_set_msr_common(vcpu, msr_info);
+ }
+
+ return ret;
+}
+
static void pvm_setup_mce(struct kvm_vcpu *vcpu)
{
}
@@ -764,6 +946,9 @@ static struct kvm_x86_ops pvm_x86_ops __initdata = {
.vcpu_load = pvm_vcpu_load,
.vcpu_put = pvm_vcpu_put,

+ .get_msr_feature = pvm_get_msr_feature,
+ .get_msr = pvm_get_msr,
+ .set_msr = pvm_set_msr,
.load_mmu_pgd = pvm_load_mmu_pgd,

.vcpu_pre_run = pvm_vcpu_pre_run,
@@ -779,6 +964,9 @@ static struct kvm_x86_ops pvm_x86_ops __initdata = {
.nested_ops = &pvm_nested_ops,

.setup_mce = pvm_setup_mce,
+
+ .msr_filter_changed = pvm_msr_filter_changed,
+ .complete_emulated_msr = kvm_complete_insn_gp,
};

static struct kvm_x86_init_ops pvm_init_ops __initdata = {
diff --git a/arch/x86/kvm/pvm/pvm.h b/arch/x86/kvm/pvm/pvm.h
index 123cfe1c3c6a..57ca2e901e0d 100644
--- a/arch/x86/kvm/pvm/pvm.h
+++ b/arch/x86/kvm/pvm/pvm.h
@@ -54,6 +54,13 @@ struct vcpu_pvm {
struct gfn_to_pfn_cache pvcs_gpc;

// emulated x86 msrs
+ u64 msr_lstar;
+ u64 msr_syscall_mask;
+ u64 msr_star;
+ u64 unused_MSR_CSTAR;
+ u64 unused_MSR_IA32_SYSENTER_CS;
+ u64 unused_MSR_IA32_SYSENTER_EIP;
+ u64 unused_MSR_IA32_SYSENTER_ESP;
u64 msr_tsc_aux;
/*
* Only bits masked by msr_ia32_feature_control_valid_bits can be set in
--
2.19.1.6.gb485710b