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KVM: SVM: keep DR6 synchronized with vcpu->arch.dr6
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kvm_x86_ops.set_dr6 is only ever called with vcpu->arch.dr6 as the
second argument.  Ensure that the VMCB value is synchronized to
vcpu->arch.dr6 on #DB (both "normal" and nested) and nested vmentry, so
that the current value of DR6 is always available in vcpu->arch.dr6.
The get_dr6 callback can just access vcpu->arch.dr6 and becomes redundant.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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bonzini committed May 8, 2020
1 parent 2c19dba commit 5679b80
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Showing 5 changed files with 21 additions and 28 deletions.
2 changes: 1 addition & 1 deletion arch/x86/include/asm/kvm_host.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1093,7 +1093,6 @@ struct kvm_x86_ops {
void (*set_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
void (*get_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
void (*set_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
u64 (*get_dr6)(struct kvm_vcpu *vcpu);
void (*set_dr6)(struct kvm_vcpu *vcpu, unsigned long value);
void (*sync_dirty_debug_regs)(struct kvm_vcpu *vcpu);
void (*set_dr7)(struct kvm_vcpu *vcpu, unsigned long value);
Expand Down Expand Up @@ -1624,6 +1623,7 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,

void kvm_define_shared_msr(unsigned index, u32 msr);
int kvm_set_shared_msr(unsigned index, u64 val, u64 mask);
void kvm_update_dr6(struct kvm_vcpu *vcpu);

u64 kvm_scale_tsc(struct kvm_vcpu *vcpu, u64 tsc);
u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc);
Expand Down
24 changes: 16 additions & 8 deletions arch/x86/kvm/svm/nested.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
#include <linux/kernel.h>

#include <asm/msr-index.h>
#include <asm/debugreg.h>

#include "kvm_emulate.h"
#include "trace.h"
Expand Down Expand Up @@ -267,7 +268,8 @@ void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
svm->vmcb->save.rsp = nested_vmcb->save.rsp;
svm->vmcb->save.rip = nested_vmcb->save.rip;
svm->vmcb->save.dr7 = nested_vmcb->save.dr7;
svm->vmcb->save.dr6 = nested_vmcb->save.dr6;
svm->vcpu.arch.dr6 = nested_vmcb->save.dr6;
kvm_update_dr6(&svm->vcpu);
svm->vmcb->save.cpl = nested_vmcb->save.cpl;

svm->nested.vmcb_msrpm = nested_vmcb->control.msrpm_base_pa & ~0x0fffULL;
Expand Down Expand Up @@ -482,7 +484,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
nested_vmcb->save.rsp = vmcb->save.rsp;
nested_vmcb->save.rax = vmcb->save.rax;
nested_vmcb->save.dr7 = vmcb->save.dr7;
nested_vmcb->save.dr6 = vmcb->save.dr6;
nested_vmcb->save.dr6 = svm->vcpu.arch.dr6;
nested_vmcb->save.cpl = vmcb->save.cpl;

nested_vmcb->control.int_ctl = vmcb->control.int_ctl;
Expand Down Expand Up @@ -606,7 +608,7 @@ static int nested_svm_exit_handled_msr(struct vcpu_svm *svm)
/* DB exceptions for our internal use must not cause vmexit */
static int nested_svm_intercept_db(struct vcpu_svm *svm)
{
unsigned long dr6;
unsigned long dr6 = svm->vmcb->save.dr6;

/* Always catch it and pass it to userspace if debugging. */
if (svm->vcpu.guest_debug &
Expand All @@ -615,22 +617,28 @@ static int nested_svm_intercept_db(struct vcpu_svm *svm)

/* if we're not singlestepping, it's not ours */
if (!svm->nmi_singlestep)
return NESTED_EXIT_DONE;
goto reflected_db;

/* if it's not a singlestep exception, it's not ours */
if (kvm_get_dr(&svm->vcpu, 6, &dr6))
return NESTED_EXIT_DONE;
if (!(dr6 & DR6_BS))
return NESTED_EXIT_DONE;
goto reflected_db;

/* if the guest is singlestepping, it should get the vmexit */
if (svm->nmi_singlestep_guest_rflags & X86_EFLAGS_TF) {
disable_nmi_singlestep(svm);
return NESTED_EXIT_DONE;
goto reflected_db;
}

/* it's ours, the nested hypervisor must not see this one */
return NESTED_EXIT_HOST;

reflected_db:
/*
* Synchronize guest DR6 here just like in db_interception; it will
* be moved into the nested VMCB by nested_svm_vmexit.
*/
svm->vcpu.arch.dr6 = dr6;
return NESTED_EXIT_DONE;
}

static int nested_svm_intercept_ioio(struct vcpu_svm *svm)
Expand Down
9 changes: 2 additions & 7 deletions arch/x86/kvm/svm/svm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1672,11 +1672,6 @@ static void new_asid(struct vcpu_svm *svm, struct svm_cpu_data *sd)
mark_dirty(svm->vmcb, VMCB_ASID);
}

static u64 svm_get_dr6(struct kvm_vcpu *vcpu)
{
return to_svm(vcpu)->vmcb->save.dr6;
}

static void svm_set_dr6(struct kvm_vcpu *vcpu, unsigned long value)
{
struct vcpu_svm *svm = to_svm(vcpu);
Expand All @@ -1693,7 +1688,7 @@ static void svm_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)
get_debugreg(vcpu->arch.db[1], 1);
get_debugreg(vcpu->arch.db[2], 2);
get_debugreg(vcpu->arch.db[3], 3);
vcpu->arch.dr6 = svm_get_dr6(vcpu);
vcpu->arch.dr6 = svm->vmcb->save.dr6;
vcpu->arch.dr7 = svm->vmcb->save.dr7;

vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_WONT_EXIT;
Expand Down Expand Up @@ -1739,6 +1734,7 @@ static int db_interception(struct vcpu_svm *svm)
if (!(svm->vcpu.guest_debug &
(KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP)) &&
!svm->nmi_singlestep) {
vcpu->arch.dr6 = svm->vmcb->save.dr6;
kvm_queue_exception(&svm->vcpu, DB_VECTOR);
return 1;
}
Expand Down Expand Up @@ -3931,7 +3927,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
.set_idt = svm_set_idt,
.get_gdt = svm_get_gdt,
.set_gdt = svm_set_gdt,
.get_dr6 = svm_get_dr6,
.set_dr6 = svm_set_dr6,
.set_dr7 = svm_set_dr7,
.sync_dirty_debug_regs = svm_sync_dirty_debug_regs,
Expand Down
6 changes: 0 additions & 6 deletions arch/x86/kvm/vmx/vmx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4965,11 +4965,6 @@ static int handle_dr(struct kvm_vcpu *vcpu)
return kvm_skip_emulated_instruction(vcpu);
}

static u64 vmx_get_dr6(struct kvm_vcpu *vcpu)
{
return vcpu->arch.dr6;
}

static void vmx_set_dr6(struct kvm_vcpu *vcpu, unsigned long val)
{
}
Expand Down Expand Up @@ -7736,7 +7731,6 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
.set_idt = vmx_set_idt,
.get_gdt = vmx_get_gdt,
.set_gdt = vmx_set_gdt,
.get_dr6 = vmx_get_dr6,
.set_dr6 = vmx_set_dr6,
.set_dr7 = vmx_set_dr7,
.sync_dirty_debug_regs = vmx_sync_dirty_debug_regs,
Expand Down
8 changes: 2 additions & 6 deletions arch/x86/kvm/x86.c
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Original file line number Diff line number Diff line change
Expand Up @@ -104,7 +104,6 @@ static u64 __read_mostly cr4_reserved_bits = CR4_RESERVED_BITS;
KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK)

static void update_cr8_intercept(struct kvm_vcpu *vcpu);
static void kvm_update_dr6(struct kvm_vcpu *vcpu);
static void process_nmi(struct kvm_vcpu *vcpu);
static void enter_smm(struct kvm_vcpu *vcpu);
static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
Expand Down Expand Up @@ -1048,7 +1047,7 @@ static void kvm_update_dr0123(struct kvm_vcpu *vcpu)
}
}

static void kvm_update_dr6(struct kvm_vcpu *vcpu)
void kvm_update_dr6(struct kvm_vcpu *vcpu)
{
if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
kvm_x86_ops.set_dr6(vcpu, vcpu->arch.dr6);
Expand Down Expand Up @@ -1129,10 +1128,7 @@ int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
case 4:
/* fall through */
case 6:
if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
*val = vcpu->arch.dr6;
else
*val = kvm_x86_ops.get_dr6(vcpu);
*val = vcpu->arch.dr6;
break;
case 5:
/* fall through */
Expand Down

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