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KVM: New guest debug interface
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This rips out the support for KVM_DEBUG_GUEST and introduces a new IOCTL
instead: KVM_SET_GUEST_DEBUG. The IOCTL payload consists of a generic
part, controlling the "main switch" and the single-step feature. The
arch specific part adds an x86 interface for intercepting both types of
debug exceptions separately and re-injecting them when the host was not
interested. Moveover, the foundation for guest debugging via debug
registers is layed.

To signal breakpoint events properly back to userland, an arch-specific
data block is now returned along KVM_EXIT_DEBUG. For x86, the arch block
contains the PC, the debug exception, and relevant debug registers to
tell debug events properly apart.

The availability of this new interface is signaled by
KVM_CAP_SET_GUEST_DEBUG. Empty stubs for not yet supported archs are
provided.

Note that both SVM and VTX are supported, but only the latter was tested
yet. Based on the experience with all those VTX corner case, I would be
fairly surprised if SVM will work out of the box.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
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Jan Kiszka authored and Avi Kivity committed Mar 24, 2009
1 parent 8ab2d2e commit d0bfb94
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Showing 14 changed files with 179 additions and 101 deletions.
7 changes: 7 additions & 0 deletions arch/ia64/include/asm/kvm.h
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Expand Up @@ -214,4 +214,11 @@ struct kvm_sregs {
struct kvm_fpu {
};

struct kvm_debug_exit_arch {
};

/* for KVM_SET_GUEST_DEBUG */
struct kvm_guest_debug_arch {
};

#endif
4 changes: 2 additions & 2 deletions arch/ia64/kvm/kvm-ia64.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1303,8 +1303,8 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
return -EINVAL;
}

int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
struct kvm_debug_guest *dbg)
int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
struct kvm_guest_debug *dbg)
{
return -EINVAL;
}
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7 changes: 7 additions & 0 deletions arch/powerpc/include/asm/kvm.h
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Expand Up @@ -52,4 +52,11 @@ struct kvm_fpu {
__u64 fpr[32];
};

struct kvm_debug_exit_arch {
};

/* for KVM_SET_GUEST_DEBUG */
struct kvm_guest_debug_arch {
};

#endif /* __LINUX_KVM_POWERPC_H */
4 changes: 2 additions & 2 deletions arch/powerpc/kvm/powerpc.c
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Expand Up @@ -240,8 +240,8 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
kvmppc_core_vcpu_put(vcpu);
}

int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
struct kvm_debug_guest *dbg)
int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
struct kvm_guest_debug *dbg)
{
int i;

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7 changes: 7 additions & 0 deletions arch/s390/include/asm/kvm.h
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Expand Up @@ -42,4 +42,11 @@ struct kvm_fpu {
__u64 fprs[16];
};

struct kvm_debug_exit_arch {
};

/* for KVM_SET_GUEST_DEBUG */
struct kvm_guest_debug_arch {
};

#endif
4 changes: 2 additions & 2 deletions arch/s390/kvm/kvm-s390.c
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Original file line number Diff line number Diff line change
Expand Up @@ -422,8 +422,8 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
return -EINVAL; /* not implemented yet */
}

int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
struct kvm_debug_guest *dbg)
int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
struct kvm_guest_debug *dbg)
{
return -EINVAL; /* not implemented yet */
}
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18 changes: 18 additions & 0 deletions arch/x86/include/asm/kvm.h
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Expand Up @@ -212,6 +212,24 @@ struct kvm_pit_channel_state {
__s64 count_load_time;
};

struct kvm_debug_exit_arch {
__u32 exception;
__u32 pad;
__u64 pc;
__u64 dr6;
__u64 dr7;
};

#define KVM_GUESTDBG_USE_SW_BP 0x00010000
#define KVM_GUESTDBG_USE_HW_BP 0x00020000
#define KVM_GUESTDBG_INJECT_DB 0x00040000
#define KVM_GUESTDBG_INJECT_BP 0x00080000

/* for KVM_SET_GUEST_DEBUG */
struct kvm_guest_debug_arch {
__u64 debugreg[8];
};

struct kvm_pit_state {
struct kvm_pit_channel_state channels[3];
};
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9 changes: 1 addition & 8 deletions arch/x86/include/asm/kvm_host.h
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Expand Up @@ -135,12 +135,6 @@ enum {

#define KVM_NR_MEM_OBJS 40

struct kvm_guest_debug {
int enabled;
unsigned long bp[4];
int singlestep;
};

/*
* We don't want allocation failures within the mmu code, so we preallocate
* enough memory for a single page fault in a cache.
Expand Down Expand Up @@ -448,8 +442,7 @@ struct kvm_x86_ops {
void (*vcpu_put)(struct kvm_vcpu *vcpu);

int (*set_guest_debug)(struct kvm_vcpu *vcpu,
struct kvm_debug_guest *dbg);
void (*guest_debug_pre)(struct kvm_vcpu *vcpu);
struct kvm_guest_debug *dbg);
int (*get_msr)(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata);
int (*set_msr)(struct kvm_vcpu *vcpu, u32 msr_index, u64 data);
u64 (*get_segment_base)(struct kvm_vcpu *vcpu, int seg);
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50 changes: 48 additions & 2 deletions arch/x86/kvm/svm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -968,9 +968,32 @@ static void svm_set_segment(struct kvm_vcpu *vcpu,

}

static int svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_debug_guest *dbg)
static int svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
{
return -EOPNOTSUPP;
int old_debug = vcpu->guest_debug;
struct vcpu_svm *svm = to_svm(vcpu);

vcpu->guest_debug = dbg->control;

svm->vmcb->control.intercept_exceptions &=
~((1 << DB_VECTOR) | (1 << BP_VECTOR));
if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) {
if (vcpu->guest_debug &
(KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
svm->vmcb->control.intercept_exceptions |=
1 << DB_VECTOR;
if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
svm->vmcb->control.intercept_exceptions |=
1 << BP_VECTOR;
} else
vcpu->guest_debug = 0;

if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
svm->vmcb->save.rflags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
else if (old_debug & KVM_GUESTDBG_SINGLESTEP)
svm->vmcb->save.rflags &= ~(X86_EFLAGS_TF | X86_EFLAGS_RF);

return 0;
}

static int svm_get_irq(struct kvm_vcpu *vcpu)
Expand Down Expand Up @@ -1094,6 +1117,27 @@ static int pf_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
return kvm_mmu_page_fault(&svm->vcpu, fault_address, error_code);
}

static int db_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
{
if (!(svm->vcpu.guest_debug &
(KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))) {
kvm_queue_exception(&svm->vcpu, DB_VECTOR);
return 1;
}
kvm_run->exit_reason = KVM_EXIT_DEBUG;
kvm_run->debug.arch.pc = svm->vmcb->save.cs.base + svm->vmcb->save.rip;
kvm_run->debug.arch.exception = DB_VECTOR;
return 0;
}

static int bp_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
{
kvm_run->exit_reason = KVM_EXIT_DEBUG;
kvm_run->debug.arch.pc = svm->vmcb->save.cs.base + svm->vmcb->save.rip;
kvm_run->debug.arch.exception = BP_VECTOR;
return 0;
}

static int ud_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
{
int er;
Expand Down Expand Up @@ -2050,6 +2094,8 @@ static int (*svm_exit_handlers[])(struct vcpu_svm *svm,
[SVM_EXIT_WRITE_DR3] = emulate_on_interception,
[SVM_EXIT_WRITE_DR5] = emulate_on_interception,
[SVM_EXIT_WRITE_DR7] = emulate_on_interception,
[SVM_EXIT_EXCP_BASE + DB_VECTOR] = db_interception,
[SVM_EXIT_EXCP_BASE + BP_VECTOR] = bp_interception,
[SVM_EXIT_EXCP_BASE + UD_VECTOR] = ud_interception,
[SVM_EXIT_EXCP_BASE + PF_VECTOR] = pf_interception,
[SVM_EXIT_EXCP_BASE + NM_VECTOR] = nm_interception,
Expand Down
93 changes: 36 additions & 57 deletions arch/x86/kvm/vmx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -480,8 +480,13 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
eb = (1u << PF_VECTOR) | (1u << UD_VECTOR);
if (!vcpu->fpu_active)
eb |= 1u << NM_VECTOR;
if (vcpu->guest_debug.enabled)
eb |= 1u << DB_VECTOR;
if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) {
if (vcpu->guest_debug &
(KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
eb |= 1u << DB_VECTOR;
if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
eb |= 1u << BP_VECTOR;
}
if (vcpu->arch.rmode.active)
eb = ~0;
if (vm_need_ept())
Expand Down Expand Up @@ -1003,40 +1008,23 @@ static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
}
}

static int set_guest_debug(struct kvm_vcpu *vcpu, struct kvm_debug_guest *dbg)
static int set_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
{
unsigned long dr7 = 0x400;
int old_singlestep;

old_singlestep = vcpu->guest_debug.singlestep;

vcpu->guest_debug.enabled = dbg->enabled;
if (vcpu->guest_debug.enabled) {
int i;

dr7 |= 0x200; /* exact */
for (i = 0; i < 4; ++i) {
if (!dbg->breakpoints[i].enabled)
continue;
vcpu->guest_debug.bp[i] = dbg->breakpoints[i].address;
dr7 |= 2 << (i*2); /* global enable */
dr7 |= 0 << (i*4+16); /* execution breakpoint */
}

vcpu->guest_debug.singlestep = dbg->singlestep;
} else
vcpu->guest_debug.singlestep = 0;
int old_debug = vcpu->guest_debug;
unsigned long flags;

if (old_singlestep && !vcpu->guest_debug.singlestep) {
unsigned long flags;
vcpu->guest_debug = dbg->control;
if (!(vcpu->guest_debug & KVM_GUESTDBG_ENABLE))
vcpu->guest_debug = 0;

flags = vmcs_readl(GUEST_RFLAGS);
flags = vmcs_readl(GUEST_RFLAGS);
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
flags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
else if (old_debug & KVM_GUESTDBG_SINGLESTEP)
flags &= ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
vmcs_writel(GUEST_RFLAGS, flags);
}
vmcs_writel(GUEST_RFLAGS, flags);

update_exception_bitmap(vcpu);
vmcs_writel(GUEST_DR7, dr7);

return 0;
}
Expand Down Expand Up @@ -2540,24 +2528,6 @@ static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr)
return 0;
}

static void kvm_guest_debug_pre(struct kvm_vcpu *vcpu)
{
struct kvm_guest_debug *dbg = &vcpu->guest_debug;

set_debugreg(dbg->bp[0], 0);
set_debugreg(dbg->bp[1], 1);
set_debugreg(dbg->bp[2], 2);
set_debugreg(dbg->bp[3], 3);

if (dbg->singlestep) {
unsigned long flags;

flags = vmcs_readl(GUEST_RFLAGS);
flags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
vmcs_writel(GUEST_RFLAGS, flags);
}
}

static int handle_rmode_exception(struct kvm_vcpu *vcpu,
int vec, u32 err_code)
{
Expand All @@ -2574,9 +2544,17 @@ static int handle_rmode_exception(struct kvm_vcpu *vcpu,
* the required debugging infrastructure rework.
*/
switch (vec) {
case DE_VECTOR:
case DB_VECTOR:
if (vcpu->guest_debug &
(KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
return 0;
kvm_queue_exception(vcpu, vec);
return 1;
case BP_VECTOR:
if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
return 0;
/* fall through */
case DE_VECTOR:
case OF_VECTOR:
case BR_VECTOR:
case UD_VECTOR:
Expand All @@ -2593,7 +2571,7 @@ static int handle_rmode_exception(struct kvm_vcpu *vcpu,
static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
u32 intr_info, error_code;
u32 intr_info, ex_no, error_code;
unsigned long cr2, rip;
u32 vect_info;
enum emulation_result er;
Expand Down Expand Up @@ -2653,14 +2631,16 @@ static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
return 1;
}

if ((intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VECTOR_MASK)) ==
(INTR_TYPE_HARD_EXCEPTION | 1)) {
ex_no = intr_info & INTR_INFO_VECTOR_MASK;
if (ex_no == DB_VECTOR || ex_no == BP_VECTOR) {
kvm_run->exit_reason = KVM_EXIT_DEBUG;
return 0;
kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip;
kvm_run->debug.arch.exception = ex_no;
} else {
kvm_run->exit_reason = KVM_EXIT_EXCEPTION;
kvm_run->ex.exception = ex_no;
kvm_run->ex.error_code = error_code;
}
kvm_run->exit_reason = KVM_EXIT_EXCEPTION;
kvm_run->ex.exception = intr_info & INTR_INFO_VECTOR_MASK;
kvm_run->ex.error_code = error_code;
return 0;
}

Expand Down Expand Up @@ -3600,7 +3580,6 @@ static struct kvm_x86_ops vmx_x86_ops = {
.vcpu_put = vmx_vcpu_put,

.set_guest_debug = set_guest_debug,
.guest_debug_pre = kvm_guest_debug_pre,
.get_msr = vmx_get_msr,
.set_msr = vmx_set_msr,
.get_segment_base = vmx_get_segment_base,
Expand Down
14 changes: 8 additions & 6 deletions arch/x86/kvm/x86.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3005,9 +3005,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
goto out;
}

if (vcpu->guest_debug.enabled)
kvm_x86_ops->guest_debug_pre(vcpu);

vcpu->guest_mode = 1;
/*
* Make sure that guest_mode assignment won't happen after
Expand Down Expand Up @@ -3218,7 +3215,7 @@ int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
/*
* Don't leak debug flags in case they were set for guest debugging
*/
if (vcpu->guest_debug.enabled && vcpu->guest_debug.singlestep)
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
regs->rflags &= ~(X86_EFLAGS_TF | X86_EFLAGS_RF);

vcpu_put(vcpu);
Expand Down Expand Up @@ -3837,15 +3834,20 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
return 0;
}

int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
struct kvm_debug_guest *dbg)
int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
struct kvm_guest_debug *dbg)
{
int r;

vcpu_load(vcpu);

r = kvm_x86_ops->set_guest_debug(vcpu, dbg);

if (dbg->control & KVM_GUESTDBG_INJECT_DB)
kvm_queue_exception(vcpu, DB_VECTOR);
else if (dbg->control & KVM_GUESTDBG_INJECT_BP)
kvm_queue_exception(vcpu, BP_VECTOR);

vcpu_put(vcpu);

return r;
Expand Down
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