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KVM: x86: drop TSC offsetting kvm_x86_ops to fix KVM_GET/SET_CLOCK
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Since commit a545ab6 ("kvm: x86: add tsc_offset field to struct
kvm_vcpu_arch", 2016-09-07) the offset between host and L1 TSC is
cached and need not be fished out of the VMCS or VMCB.  This means
that we can implement adjust_tsc_offset_guest and read_l1_tsc
entirely in generic code.  The simplification is particularly
significant for VMX code, where vmx->nested.vmcs01_tsc_offset
was duplicating what is now in vcpu->arch.tsc_offset.  Therefore
the vmcs01_tsc_offset can be dropped completely.

More importantly, this fixes KVM_GET_CLOCK/KVM_SET_CLOCK
which, after commit 108b249 ("KVM: x86: introduce get_kvmclock_ns",
2016-09-01) called read_l1_tsc while the VMCS was not loaded.
It thus returned bogus values on Intel CPUs.

Fixes: 108b249
Reported-by: Roman Kagan <rkagan@virtuozzo.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Paolo Bonzini committed Nov 2, 2016
1 parent bd768e1 commit ea26e4e
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Showing 4 changed files with 6 additions and 65 deletions.
3 changes: 0 additions & 3 deletions arch/x86/include/asm/kvm_host.h
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Original file line number Diff line number Diff line change
Expand Up @@ -948,7 +948,6 @@ struct kvm_x86_ops {
int (*get_lpage_level)(void);
bool (*rdtscp_supported)(void);
bool (*invpcid_supported)(void);
void (*adjust_tsc_offset_guest)(struct kvm_vcpu *vcpu, s64 adjustment);

void (*set_tdp_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);

Expand All @@ -958,8 +957,6 @@ struct kvm_x86_ops {

void (*write_tsc_offset)(struct kvm_vcpu *vcpu, u64 offset);

u64 (*read_l1_tsc)(struct kvm_vcpu *vcpu, u64 host_tsc);

void (*get_exit_info)(struct kvm_vcpu *vcpu, u64 *info1, u64 *info2);

int (*check_intercept)(struct kvm_vcpu *vcpu,
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23 changes: 0 additions & 23 deletions arch/x86/kvm/svm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1138,21 +1138,6 @@ static void svm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
mark_dirty(svm->vmcb, VMCB_INTERCEPTS);
}

static void svm_adjust_tsc_offset_guest(struct kvm_vcpu *vcpu, s64 adjustment)
{
struct vcpu_svm *svm = to_svm(vcpu);

svm->vmcb->control.tsc_offset += adjustment;
if (is_guest_mode(vcpu))
svm->nested.hsave->control.tsc_offset += adjustment;
else
trace_kvm_write_tsc_offset(vcpu->vcpu_id,
svm->vmcb->control.tsc_offset - adjustment,
svm->vmcb->control.tsc_offset);

mark_dirty(svm->vmcb, VMCB_INTERCEPTS);
}

static void avic_init_vmcb(struct vcpu_svm *svm)
{
struct vmcb *vmcb = svm->vmcb;
Expand Down Expand Up @@ -3449,12 +3434,6 @@ static int cr8_write_interception(struct vcpu_svm *svm)
return 0;
}

static u64 svm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc)
{
struct vmcb *vmcb = get_host_vmcb(to_svm(vcpu));
return vmcb->control.tsc_offset + host_tsc;
}

static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
{
struct vcpu_svm *svm = to_svm(vcpu);
Expand Down Expand Up @@ -5422,8 +5401,6 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
.has_wbinvd_exit = svm_has_wbinvd_exit,

.write_tsc_offset = svm_write_tsc_offset,
.adjust_tsc_offset_guest = svm_adjust_tsc_offset_guest,
.read_l1_tsc = svm_read_l1_tsc,

.set_tdp_cr3 = set_tdp_cr3,

Expand Down
39 changes: 3 additions & 36 deletions arch/x86/kvm/vmx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -421,7 +421,6 @@ struct nested_vmx {
/* vmcs02_list cache of VMCSs recently used to run L2 guests */
struct list_head vmcs02_pool;
int vmcs02_num;
u64 vmcs01_tsc_offset;
bool change_vmcs01_virtual_x2apic_mode;
/* L2 must run next, and mustn't decide to exit to L1. */
bool nested_run_pending;
Expand Down Expand Up @@ -2604,20 +2603,6 @@ static u64 guest_read_tsc(struct kvm_vcpu *vcpu)
return kvm_scale_tsc(vcpu, host_tsc) + tsc_offset;
}

/*
* Like guest_read_tsc, but always returns L1's notion of the timestamp
* counter, even if a nested guest (L2) is currently running.
*/
static u64 vmx_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc)
{
u64 tsc_offset;

tsc_offset = is_guest_mode(vcpu) ?
to_vmx(vcpu)->nested.vmcs01_tsc_offset :
vmcs_read64(TSC_OFFSET);
return host_tsc + tsc_offset;
}

/*
* writes 'offset' into guest's timestamp counter offset register
*/
Expand All @@ -2631,7 +2616,6 @@ static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
* to the newly set TSC to get L2's TSC.
*/
struct vmcs12 *vmcs12;
to_vmx(vcpu)->nested.vmcs01_tsc_offset = offset;
/* recalculate vmcs02.TSC_OFFSET: */
vmcs12 = get_vmcs12(vcpu);
vmcs_write64(TSC_OFFSET, offset +
Expand All @@ -2644,19 +2628,6 @@ static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
}
}

static void vmx_adjust_tsc_offset_guest(struct kvm_vcpu *vcpu, s64 adjustment)
{
u64 offset = vmcs_read64(TSC_OFFSET);

vmcs_write64(TSC_OFFSET, offset + adjustment);
if (is_guest_mode(vcpu)) {
/* Even when running L2, the adjustment needs to apply to L1 */
to_vmx(vcpu)->nested.vmcs01_tsc_offset += adjustment;
} else
trace_kvm_write_tsc_offset(vcpu->vcpu_id, offset,
offset + adjustment);
}

static bool guest_cpuid_has_vmx(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *best = kvm_find_cpuid_entry(vcpu, 1, 0);
Expand Down Expand Up @@ -10061,9 +10032,9 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)

if (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING)
vmcs_write64(TSC_OFFSET,
vmx->nested.vmcs01_tsc_offset + vmcs12->tsc_offset);
vcpu->arch.tsc_offset + vmcs12->tsc_offset);
else
vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);
vmcs_write64(TSC_OFFSET, vcpu->arch.tsc_offset);
if (kvm_has_tsc_control)
decache_tsc_multiplier(vmx);

Expand Down Expand Up @@ -10293,8 +10264,6 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)

enter_guest_mode(vcpu);

vmx->nested.vmcs01_tsc_offset = vmcs_read64(TSC_OFFSET);

if (!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS))
vmx->nested.vmcs01_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL);

Expand Down Expand Up @@ -10818,7 +10787,7 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
load_vmcs12_host_state(vcpu, vmcs12);

/* Update any VMCS fields that might have changed while L2 ran */
vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);
vmcs_write64(TSC_OFFSET, vcpu->arch.tsc_offset);
if (vmx->hv_deadline_tsc == -1)
vmcs_clear_bits(PIN_BASED_VM_EXEC_CONTROL,
PIN_BASED_VMX_PREEMPTION_TIMER);
Expand Down Expand Up @@ -11339,8 +11308,6 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
.has_wbinvd_exit = cpu_has_vmx_wbinvd_exit,

.write_tsc_offset = vmx_write_tsc_offset,
.adjust_tsc_offset_guest = vmx_adjust_tsc_offset_guest,
.read_l1_tsc = vmx_read_l1_tsc,

.set_tdp_cr3 = vmx_set_cr3,

Expand Down
6 changes: 3 additions & 3 deletions arch/x86/kvm/x86.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1409,7 +1409,7 @@ static u64 kvm_compute_tsc_offset(struct kvm_vcpu *vcpu, u64 target_tsc)

u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc)
{
return kvm_x86_ops->read_l1_tsc(vcpu, kvm_scale_tsc(vcpu, host_tsc));
return vcpu->arch.tsc_offset + kvm_scale_tsc(vcpu, host_tsc);
}
EXPORT_SYMBOL_GPL(kvm_read_l1_tsc);

Expand Down Expand Up @@ -1547,15 +1547,15 @@ EXPORT_SYMBOL_GPL(kvm_write_tsc);
static inline void adjust_tsc_offset_guest(struct kvm_vcpu *vcpu,
s64 adjustment)
{
kvm_x86_ops->adjust_tsc_offset_guest(vcpu, adjustment);
kvm_vcpu_write_tsc_offset(vcpu, vcpu->arch.tsc_offset + adjustment);
}

static inline void adjust_tsc_offset_host(struct kvm_vcpu *vcpu, s64 adjustment)
{
if (vcpu->arch.tsc_scaling_ratio != kvm_default_tsc_scaling_ratio)
WARN_ON(adjustment < 0);
adjustment = kvm_scale_tsc(vcpu, (u64) adjustment);
kvm_x86_ops->adjust_tsc_offset_guest(vcpu, adjustment);
adjust_tsc_offset_guest(vcpu, adjustment);
}

#ifdef CONFIG_X86_64
Expand Down

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