@@ -4869,8 +4869,8 @@ to the byte array.
.. note::
- For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_PAPR and
- KVM_EXIT_EPR the corresponding
+ For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_PAPR,
+ KVM_EXIT_EPR, KVM_EXIT_X86_RDMSR and KVM_EXIT_X86_WRMSR the corresponding
operations are complete (and guest state is consistent) only after userspace
has re-entered the kernel with KVM_RUN. The kernel side will first finish
@@ -5163,6 +5163,43 @@ Note that KVM does not skip the faulting instruction as it does for
KVM_EXIT_MMIO, but userspace has to emulate any change to the processing state
if it decides to decode and emulate the instruction.
+::
+
+ /* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */
+ struct {
+ __u8 error; /* user -> kernel */
+ __u8 pad[7];
+ __u32 reason; /* kernel -> user */
+ __u32 index; /* kernel -> user */
+ __u64 data; /* kernel <-> user */
+ } msr;
+
+Used on x86 systems. When the VM capability KVM_CAP_X86_USER_SPACE_MSR is
+enabled, MSR accesses to registers that would invoke a #GP by KVM kernel code
+will instead trigger a KVM_EXIT_X86_RDMSR exit for reads and KVM_EXIT_X86_WRMSR
+exit for writes.
+
+The "reason" field specifies why the MSR trap occurred. User space will only
+receive MSR exit traps when a particular reason was requested during through
+ENABLE_CAP. Currently valid exit reasons are:
+
+ KVM_MSR_EXIT_REASON_UNKNOWN - access to MSR that is unknown to KVM
+ KVM_MSR_EXIT_REASON_INVAL - access to invalid MSRs or reserved bits
+
+For KVM_EXIT_X86_RDMSR, the "index" field tells user space which MSR the guest
+wants to read. To respond to this request with a successful read, user space
+writes the respective data into the "data" field and must continue guest
+execution to ensure the read data is transferred into guest register state.
+
+If the RDMSR request was unsuccessful, user space indicates that with a "1" in
+the "error" field. This will inject a #GP into the guest when the VCPU is
+executed again.
+
+For KVM_EXIT_X86_WRMSR, the "index" field tells user space which MSR the guest
+wants to write. Once finished processing the event, user space must continue
+vCPU execution. If the MSR write was unsuccessful, user space also sets the
+"error" field to "1".
+
::
/* Fix the size of the union. */
@@ -5852,6 +5889,28 @@ controlled by the kvm module parameter halt_poll_ns. This capability allows
the maximum halt time to specified on a per-VM basis, effectively overriding
the module parameter for the target VM.
+7.21 KVM_CAP_X86_USER_SPACE_MSR
+-------------------------------
+
+:Architectures: x86
+:Target: VM
+:Parameters: args[0] contains the mask of KVM_MSR_EXIT_REASON_* events to report
+:Returns: 0 on success; -1 on error
+
+This capability enables trapping of #GP invoking RDMSR and WRMSR instructions
+into user space.
+
+When a guest requests to read or write an MSR, KVM may not implement all MSRs
+that are relevant to a respective system. It also does not differentiate by
+CPU type.
+
+To allow more fine grained control over MSR handling, user space may enable
+this capability. With it enabled, MSR accesses that match the mask specified in
+args[0] and trigger a #GP event inside the guest by KVM will instead trigger
+KVM_EXIT_X86_RDMSR and KVM_EXIT_X86_WRMSR exit notifications which user space
+can then handle to implement model specific MSR handling and/or user notifications
+to inform a user that an MSR was not handled.
+
8. Other capabilities.
======================
@@ -6173,3 +6232,14 @@ specific interfaces must be consistent, i.e. if one says the feature
is supported, than the other should as well and vice versa. For arm64
see Documentation/virt/kvm/devices/vcpu.rst "KVM_ARM_VCPU_PVTIME_CTRL".
For x86 see Documentation/virt/kvm/msr.rst "MSR_KVM_STEAL_TIME".
+
+8.25 KVM_CAP_X86_USER_SPACE_MSR
+----------------------------
+
+:Architectures: x86
+
+This capability indicates that KVM supports deflection of MSR reads and
+writes to user space. It can be enabled on a VM level. If enabled, MSR
+accesses that would usually trigger a #GP by KVM into the guest will
+instead get bounced to user space through the KVM_EXIT_X86_RDMSR and
+KVM_EXIT_X86_WRMSR exit notifications.
@@ -961,6 +961,9 @@ struct kvm_arch {
bool guest_can_read_msr_platform_info;
bool exception_payload_enabled;
+ /* Deflect RDMSR and WRMSR to user space when they trigger a #GP */
+ u32 user_space_msr_mask;
+
struct kvm_pmu_event_filter *pmu_event_filter;
struct task_struct *nx_lpage_recovery_thread;
};
@@ -3701,11 +3701,18 @@ static int em_dr_write(struct x86_emulate_ctxt *ctxt)
static int em_wrmsr(struct x86_emulate_ctxt *ctxt)
{
+ u64 msr_index = reg_read(ctxt, VCPU_REGS_RCX);
u64 msr_data;
+ int r;
msr_data = (u32)reg_read(ctxt, VCPU_REGS_RAX)
| ((u64)reg_read(ctxt, VCPU_REGS_RDX) << 32);
- if (ctxt->ops->set_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), msr_data))
+ r = ctxt->ops->set_msr(ctxt, msr_index, msr_data);
+
+ if (r == X86EMUL_IO_NEEDED)
+ return r;
+
+ if (r)
return emulate_gp(ctxt, 0);
return X86EMUL_CONTINUE;
@@ -3713,9 +3720,16 @@ static int em_wrmsr(struct x86_emulate_ctxt *ctxt)
static int em_rdmsr(struct x86_emulate_ctxt *ctxt)
{
+ u64 msr_index = reg_read(ctxt, VCPU_REGS_RCX);
u64 msr_data;
+ int r;
+
+ r = ctxt->ops->get_msr(ctxt, msr_index, &msr_data);
+
+ if (r == X86EMUL_IO_NEEDED)
+ return r;
- if (ctxt->ops->get_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), &msr_data))
+ if (r)
return emulate_gp(ctxt, 0);
*reg_write(ctxt, VCPU_REGS_RAX) = (u32)msr_data;
@@ -1589,12 +1589,89 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data)
}
EXPORT_SYMBOL_GPL(kvm_set_msr);
+static int complete_emulated_msr(struct kvm_vcpu *vcpu, bool is_read)
+{
+ if (vcpu->run->msr.error) {
+ kvm_inject_gp(vcpu, 0);
+ return 1;
+ } else if (is_read) {
+ kvm_rax_write(vcpu, (u32)vcpu->run->msr.data);
+ kvm_rdx_write(vcpu, vcpu->run->msr.data >> 32);
+ }
+
+ return kvm_skip_emulated_instruction(vcpu);
+}
+
+static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu)
+{
+ return complete_emulated_msr(vcpu, true);
+}
+
+static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu)
+{
+ return complete_emulated_msr(vcpu, false);
+}
+
+static u64 kvm_msr_reason(int r)
+{
+ switch (r) {
+ case -ENOENT:
+ return KVM_MSR_EXIT_REASON_UNKNOWN;
+ default:
+ return KVM_MSR_EXIT_REASON_INVAL;
+ }
+}
+
+static int kvm_msr_user_space(struct kvm_vcpu *vcpu, u32 index,
+ u32 exit_reason, u64 data,
+ int (*completion)(struct kvm_vcpu *vcpu),
+ int r)
+{
+ u64 msr_reason = kvm_msr_reason(r);
+
+ /* Check if the user wanted to know about this MSR fault */
+ if (!(vcpu->kvm->arch.user_space_msr_mask & msr_reason))
+ return 0;
+
+ vcpu->run->exit_reason = exit_reason;
+ vcpu->run->msr.error = 0;
+ memset(vcpu->run->msr.pad, 0, sizeof(vcpu->run->msr.pad));
+ vcpu->run->msr.reason = msr_reason;
+ vcpu->run->msr.index = index;
+ vcpu->run->msr.data = data;
+ vcpu->arch.complete_userspace_io = completion;
+
+ return 1;
+}
+
+static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index, int r)
+{
+ return kvm_msr_user_space(vcpu, index, KVM_EXIT_X86_RDMSR, 0,
+ complete_emulated_rdmsr, r);
+}
+
+static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data, int r)
+{
+ return kvm_msr_user_space(vcpu, index, KVM_EXIT_X86_WRMSR, data,
+ complete_emulated_wrmsr, r);
+}
+
int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
{
u32 ecx = kvm_rcx_read(vcpu);
u64 data;
+ int r;
+
+ r = kvm_get_msr(vcpu, ecx, &data);
- if (kvm_get_msr(vcpu, ecx, &data)) {
+ /* MSR read failed? See if we should ask user space */
+ if (r && kvm_get_msr_user_space(vcpu, ecx, r)) {
+ /* Bounce to user space */
+ return 0;
+ }
+
+ /* MSR read failed? Inject a #GP */
+ if (r) {
trace_kvm_msr_read_ex(ecx);
kvm_inject_gp(vcpu, 0);
return 1;
@@ -1612,8 +1689,18 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
{
u32 ecx = kvm_rcx_read(vcpu);
u64 data = kvm_read_edx_eax(vcpu);
+ int r;
- if (kvm_set_msr(vcpu, ecx, data)) {
+ r = kvm_set_msr(vcpu, ecx, data);
+
+ /* MSR write failed? See if we should ask user space */
+ if (r && kvm_set_msr_user_space(vcpu, ecx, data, r)) {
+ /* Bounce to user space */
+ return 0;
+ }
+
+ /* MSR write failed? Inject a #GP */
+ if (r) {
trace_kvm_msr_write_ex(ecx, data);
kvm_inject_gp(vcpu, 0);
return 1;
@@ -3511,6 +3598,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_EXCEPTION_PAYLOAD:
case KVM_CAP_SET_GUEST_DEBUG:
case KVM_CAP_LAST_CPU:
+ case KVM_CAP_X86_USER_SPACE_MSR:
r = 1;
break;
case KVM_CAP_SYNC_REGS:
@@ -5031,6 +5119,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
kvm->arch.exception_payload_enabled = cap->args[0];
r = 0;
break;
+ case KVM_CAP_X86_USER_SPACE_MSR:
+ kvm->arch.user_space_msr_mask = cap->args[0];
+ r = 0;
+ break;
default:
r = -EINVAL;
break;
@@ -6360,13 +6452,33 @@ static void emulator_set_segment(struct x86_emulate_ctxt *ctxt, u16 selector,
static int emulator_get_msr(struct x86_emulate_ctxt *ctxt,
u32 msr_index, u64 *pdata)
{
- return kvm_get_msr(emul_to_vcpu(ctxt), msr_index, pdata);
+ struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
+ int r;
+
+ r = kvm_get_msr(vcpu, msr_index, pdata);
+
+ if (r && kvm_get_msr_user_space(vcpu, msr_index, r)) {
+ /* Bounce to user space */
+ return X86EMUL_IO_NEEDED;
+ }
+
+ return r;
}
static int emulator_set_msr(struct x86_emulate_ctxt *ctxt,
u32 msr_index, u64 data)
{
- return kvm_set_msr(emul_to_vcpu(ctxt), msr_index, data);
+ struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
+ int r;
+
+ r = kvm_set_msr(vcpu, msr_index, data);
+
+ if (r && kvm_set_msr_user_space(vcpu, msr_index, data, r)) {
+ /* Bounce to user space */
+ return X86EMUL_IO_NEEDED;
+ }
+
+ return r;
}
static u64 emulator_get_smbase(struct x86_emulate_ctxt *ctxt)
@@ -17,7 +17,7 @@
ERSN(NMI), ERSN(INTERNAL_ERROR), ERSN(OSI), ERSN(PAPR_HCALL), \
ERSN(S390_UCONTROL), ERSN(WATCHDOG), ERSN(S390_TSCH), ERSN(EPR),\
ERSN(SYSTEM_EVENT), ERSN(S390_STSI), ERSN(IOAPIC_EOI), \
- ERSN(HYPERV), ERSN(ARM_NISV)
+ ERSN(HYPERV), ERSN(ARM_NISV), ERSN(X86_RDMSR), ERSN(X86_WRMSR)
TRACE_EVENT(kvm_userspace_exit,
TP_PROTO(__u32 reason, int errno),
@@ -248,6 +248,8 @@ struct kvm_hyperv_exit {
#define KVM_EXIT_IOAPIC_EOI 26
#define KVM_EXIT_HYPERV 27
#define KVM_EXIT_ARM_NISV 28
+#define KVM_EXIT_X86_RDMSR 29
+#define KVM_EXIT_X86_WRMSR 30
/* For KVM_EXIT_INTERNAL_ERROR */
/* Emulate instruction failed. */
@@ -413,6 +415,16 @@ struct kvm_run {
__u64 esr_iss;
__u64 fault_ipa;
} arm_nisv;
+ /* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */
+ struct {
+ __u8 error; /* user -> kernel */
+ __u8 pad[7];
+#define KVM_MSR_EXIT_REASON_INVAL (1 << 0)
+#define KVM_MSR_EXIT_REASON_UNKNOWN (1 << 1)
+ __u32 reason; /* kernel -> user */
+ __u32 index; /* kernel -> user */
+ __u64 data; /* kernel <-> user */
+ } msr;
/* Fix the size of the union. */
char padding[256];
};
@@ -1037,6 +1049,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_SMALLER_MAXPHYADDR 185
#define KVM_CAP_S390_DIAG318 186
#define KVM_CAP_STEAL_TIME 187
+#define KVM_CAP_X86_USER_SPACE_MSR 188
#ifdef KVM_CAP_IRQ_ROUTING