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KVM: nVMX: Fix VMX preemption timer migration
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Add new field to hold preemption timer expiration deadline
appended to struct kvm_vmx_nested_state_hdr. This is to prevent
the first VM-Enter after migration from incorrectly restarting the timer
with the full timer value instead of partially decayed timer value.
KVM_SET_NESTED_STATE restarts timer using migrated state regardless
of whether L1 sets VM_EXIT_SAVE_VMX_PREEMPTION_TIMER.

Fixes: cf8b84f ("kvm: nVMX: Prepare for checkpointing L2 state")

Signed-off-by: Peter Shier <pshier@google.com>
Signed-off-by: Makarand Sonare <makarandsonare@google.com>
Message-Id: <20200526215107.205814-2-makarandsonare@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Peter Shier authored and Paolo Bonzini committed Jun 1, 2020
1 parent f7d31e6 commit 850448f
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Showing 4 changed files with 56 additions and 8 deletions.
4 changes: 4 additions & 0 deletions Documentation/virt/kvm/api.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -4334,9 +4334,13 @@ Errors:
#define KVM_STATE_NESTED_VMX_SMM_GUEST_MODE 0x00000001
#define KVM_STATE_NESTED_VMX_SMM_VMXON 0x00000002

#define KVM_STATE_VMX_PREEMPTION_TIMER_DEADLINE 0x00000001

struct kvm_vmx_nested_state_hdr {
__u32 flags;
__u64 vmxon_pa;
__u64 vmcs12_pa;
__u64 preemption_timer_deadline;

struct {
__u16 flags;
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3 changes: 3 additions & 0 deletions arch/x86/include/uapi/asm/kvm.h
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Original file line number Diff line number Diff line change
Expand Up @@ -400,15 +400,18 @@ struct kvm_sync_regs {

#define KVM_STATE_NESTED_SVM_VMCB_SIZE 0x1000

#define KVM_STATE_VMX_PREEMPTION_TIMER_DEADLINE 0x00000001

struct kvm_vmx_nested_state_data {
__u8 vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE];
__u8 shadow_vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE];
};

struct kvm_vmx_nested_state_hdr {
__u32 flags;
__u64 vmxon_pa;
__u64 vmcs12_pa;
__u64 preemption_timer_deadline;

struct {
__u16 flags;
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55 changes: 47 additions & 8 deletions arch/x86/kvm/vmx/nested.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2087,9 +2087,29 @@ static enum hrtimer_restart vmx_preemption_timer_fn(struct hrtimer *timer)
return HRTIMER_NORESTART;
}

static void vmx_start_preemption_timer(struct kvm_vcpu *vcpu)
static u64 vmx_calc_preemption_timer_value(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
u64 timer_value = 0;

u64 l1_scaled_tsc = kvm_read_l1_tsc(vcpu, rdtsc()) >>
VMX_MISC_EMULATED_PREEMPTION_TIMER_RATE;

if (!vmx->nested.has_preemption_timer_deadline) {
timer_value = vmcs12->vmx_preemption_timer_value;
vmx->nested.preemption_timer_deadline = timer_value +
l1_scaled_tsc;
vmx->nested.has_preemption_timer_deadline = true;
} else if (l1_scaled_tsc < vmx->nested.preemption_timer_deadline)
timer_value = vmx->nested.preemption_timer_deadline -
l1_scaled_tsc;
return timer_value;
}

static void vmx_start_preemption_timer(struct kvm_vcpu *vcpu,
u64 preemption_timeout)
{
u64 preemption_timeout = get_vmcs12(vcpu)->vmx_preemption_timer_value;
struct vcpu_vmx *vmx = to_vmx(vcpu);

/*
Expand Down Expand Up @@ -3348,8 +3368,10 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
* the timer.
*/
vmx->nested.preemption_timer_expired = false;
if (nested_cpu_has_preemption_timer(vmcs12))
vmx_start_preemption_timer(vcpu);
if (nested_cpu_has_preemption_timer(vmcs12)) {
u64 timer_value = vmx_calc_preemption_timer_value(vcpu);
vmx_start_preemption_timer(vcpu, timer_value);
}

/*
* Note no nested_vmx_succeed or nested_vmx_fail here. At this point
Expand Down Expand Up @@ -3457,6 +3479,7 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
* the nested entry.
*/
vmx->nested.nested_run_pending = 1;
vmx->nested.has_preemption_timer_deadline = false;
status = nested_vmx_enter_non_root_mode(vcpu, true);
if (unlikely(status != NVMX_VMENTRY_SUCCESS))
goto vmentry_failed;
Expand Down Expand Up @@ -3957,9 +3980,10 @@ static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
vmcs12->guest_activity_state = GUEST_ACTIVITY_ACTIVE;

if (nested_cpu_has_preemption_timer(vmcs12) &&
vmcs12->vm_exit_controls & VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)
vmcs12->vmx_preemption_timer_value =
vmx_get_preemption_timer_value(vcpu);
vmcs12->vm_exit_controls & VM_EXIT_SAVE_VMX_PREEMPTION_TIMER &&
!vmx->nested.nested_run_pending)
vmcs12->vmx_preemption_timer_value =
vmx_get_preemption_timer_value(vcpu);

/*
* In some cases (usually, nested EPT), L2 is allowed to change its
Expand Down Expand Up @@ -5891,8 +5915,10 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
.flags = 0,
.format = KVM_STATE_NESTED_FORMAT_VMX,
.size = sizeof(kvm_state),
.hdr.vmx.flags = 0,
.hdr.vmx.vmxon_pa = -1ull,
.hdr.vmx.vmcs12_pa = -1ull,
.hdr.vmx.preemption_timer_deadline = 0,
};
struct kvm_vmx_nested_state_data __user *user_vmx_nested_state =
&user_kvm_nested_state->data.vmx[0];
Expand Down Expand Up @@ -5934,6 +5960,14 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,

if (vmx->nested.mtf_pending)
kvm_state.flags |= KVM_STATE_NESTED_MTF_PENDING;

if (nested_cpu_has_preemption_timer(vmcs12) &&
vmx->nested.has_preemption_timer_deadline) {
kvm_state.hdr.vmx.flags |=
KVM_STATE_VMX_PREEMPTION_TIMER_DEADLINE;
kvm_state.hdr.vmx.preemption_timer_deadline =
vmx->nested.preemption_timer_deadline;
}
}
}

Expand Down Expand Up @@ -5979,7 +6013,6 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
get_shadow_vmcs12(vcpu), VMCS12_SIZE))
return -EFAULT;
}

out:
return kvm_state.size;
}
Expand Down Expand Up @@ -6141,6 +6174,12 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
goto error_guest_mode;
}

if (kvm_state->hdr.vmx.flags & KVM_STATE_VMX_PREEMPTION_TIMER_DEADLINE) {
vmx->nested.has_preemption_timer_deadline = true;
vmx->nested.preemption_timer_deadline =
kvm_state->hdr.vmx.preemption_timer_deadline;
}

if (nested_vmx_check_controls(vcpu, vmcs12) ||
nested_vmx_check_host_state(vcpu, vmcs12) ||
nested_vmx_check_guest_state(vcpu, vmcs12, &ignored))
Expand Down
2 changes: 2 additions & 0 deletions arch/x86/kvm/vmx/vmx.h
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Original file line number Diff line number Diff line change
Expand Up @@ -169,6 +169,8 @@ struct nested_vmx {
u16 posted_intr_nv;

struct hrtimer preemption_timer;
u64 preemption_timer_deadline;
bool has_preemption_timer_deadline;
bool preemption_timer_expired;

/* to migrate it to L2 if VM_ENTRY_LOAD_DEBUG_CONTROLS is off */
Expand Down

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