[PATCH 0/5] Debug register emulation fixes and optimizations (reloaded)

[PATCH 0/5] Debug register emulation fixes and optimizations (reloaded)

[Jan Kiszka]

Major parts of this series were already posted a while ago during the
debug register switch optimizations. This version now comes with an
additional fix for VMX (patch 1) and a rework of mov dr emulation for
SVM.

Find this series also at git://git.kiszka.org/linux-kvm.git queues/debugregs

Jan Kiszka (5):
      KVM: VMX: Fix exceptions of mov to dr
      KVM: VMX: Fix emulation of DR4 and DR5
      KVM: VMX: Clean up DR6 emulation
      KVM: SVM: Clean up and enhance mov dr emulation
      KVM: SVM: Trap all debug register accesses

 arch/x86/include/asm/kvm_host.h |    5 +-
 arch/x86/kvm/svm.c              |   78 +++++++++++++++++++++------------------
 arch/x86/kvm/vmx.c              |   67 +++++++++++++++++++--------------
 arch/x86/kvm/x86.c              |   19 +--------
 4 files changed, 84 insertions(+), 85 deletions(-)

[PATCH 1/5] KVM: VMX: Fix exceptions of mov to dr

[Jan Kiszka]

Injecting GP without an error code is a bad idea (causes unhandled guest
exits). Moreover, we must not skip the instruction if we injected an
exception.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 arch/x86/kvm/vmx.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9f56110..4903b41 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3049,6 +3049,7 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 	unsigned long val;
 	int dr, reg;
 
+	/* Do not handle if the CPL > 0, will trigger GP on re-entry */
 	if (!kvm_require_cpl(vcpu, 0))
 		return 1;
 	dr = vmcs_readl(GUEST_DR7);
@@ -3103,20 +3104,22 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 				vcpu->arch.eff_db[dr] = val;
 			break;
 		case 4 ... 5:
-			if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
+			if (kvm_read_cr4_bits(vcpu, X86_CR4_DE)) {
 				kvm_queue_exception(vcpu, UD_VECTOR);
+				return 1;
+			}
 			break;
 		case 6:
 			if (val & 0xffffffff00000000ULL) {
-				kvm_queue_exception(vcpu, GP_VECTOR);
-				break;
+				kvm_inject_gp(vcpu, 0);
+				return 1;
 			}
 			vcpu->arch.dr6 = (val & DR6_VOLATILE) | DR6_FIXED_1;
 			break;
 		case 7:
 			if (val & 0xffffffff00000000ULL) {
-				kvm_queue_exception(vcpu, GP_VECTOR);
-				break;
+				kvm_inject_gp(vcpu, 0);
+				return 1;
 			}
 			vcpu->arch.dr7 = (val & DR7_VOLATILE) | DR7_FIXED_1;
 			if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)) {

[PATCH 2/5] KVM: VMX: Fix emulation of DR4 and DR5

[Jan Kiszka]

Make sure DR4 and DR5 are aliased to DR6 and DR7, respectively, if
CR4.DE is not set.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 arch/x86/kvm/vmx.c |   35 ++++++++++++++++++++++++++---------
 1 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4903b41..834a8eb 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3043,6 +3043,15 @@ static int handle_cr(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+static int check_dr_alias(struct kvm_vcpu *vcpu)
+{
+	if (kvm_read_cr4_bits(vcpu, X86_CR4_DE)) {
+		kvm_queue_exception(vcpu, UD_VECTOR);
+		return -1;
+	}
+	return 0;
+}
+
 static int handle_dr(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification;
@@ -3085,14 +3094,20 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 		case 0 ... 3:
 			val = vcpu->arch.db[dr];
 			break;
+		case 4:
+			if (check_dr_alias(vcpu) < 0)
+				return 1;
+			/* fall through */
 		case 6:
 			val = vcpu->arch.dr6;
 			break;
-		case 7:
+		case 5:
+			if (check_dr_alias(vcpu) < 0)
+				return 1;
+			/* fall through */
+		default: /* 7 */
 			val = vcpu->arch.dr7;
 			break;
-		default:
-			val = 0;
 		}
 		kvm_register_write(vcpu, reg, val);
 	} else {
@@ -3103,12 +3118,10 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 			if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
 				vcpu->arch.eff_db[dr] = val;
 			break;
-		case 4 ... 5:
-			if (kvm_read_cr4_bits(vcpu, X86_CR4_DE)) {
-				kvm_queue_exception(vcpu, UD_VECTOR);
+		case 4:
+			if (check_dr_alias(vcpu) < 0)
 				return 1;
-			}
-			break;
+			/* fall through */
 		case 6:
 			if (val & 0xffffffff00000000ULL) {
 				kvm_inject_gp(vcpu, 0);
@@ -3116,7 +3129,11 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 			}
 			vcpu->arch.dr6 = (val & DR6_VOLATILE) | DR6_FIXED_1;
 			break;
-		case 7:
+		case 5:
+			if (check_dr_alias(vcpu) < 0)
+				return 1;
+			/* fall through */
+		default: /* 7 */
 			if (val & 0xffffffff00000000ULL) {
 				kvm_inject_gp(vcpu, 0);
 				return 1;

[PATCH 4/5] KVM: SVM: Clean up and enhance mov dr emulation

[Jan Kiszka]

Enhance mov dr instruction emulation used by SVM so that it properly
handles dr4/5: alias to dr6/7 if cr4.de is cleared. Otherwise return
EMULATE_FAIL which will let our only possible caller in that scenario,
ud_interception, re-inject UD.

We do not need to inject faults, SVM does this for us (exceptions take
precedence over instruction interceptions). For the same reason, the
value overflow checks can be removed.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 arch/x86/include/asm/kvm_host.h |    5 +--
 arch/x86/kvm/svm.c              |   64 ++++++++++++++++++---------------------
 arch/x86/kvm/x86.c              |   19 +-----------
 3 files changed, 33 insertions(+), 55 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a1f0b5d..d73ed48 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -506,9 +506,8 @@ struct kvm_x86_ops {
 	void (*set_idt)(struct kvm_vcpu *vcpu, struct descriptor_table *dt);
 	void (*get_gdt)(struct kvm_vcpu *vcpu, struct descriptor_table *dt);
 	void (*set_gdt)(struct kvm_vcpu *vcpu, struct descriptor_table *dt);
-	unsigned long (*get_dr)(struct kvm_vcpu *vcpu, int dr);
-	void (*set_dr)(struct kvm_vcpu *vcpu, int dr, unsigned long value,
-		       int *exception);
+	int (*get_dr)(struct kvm_vcpu *vcpu, int dr, unsigned long *dest);
+	int (*set_dr)(struct kvm_vcpu *vcpu, int dr, unsigned long value);
 	void (*cache_reg)(struct kvm_vcpu *vcpu, enum kvm_reg reg);
 	unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);
 	void (*set_rflags)(struct kvm_vcpu *vcpu, unsigned long rflags);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 8d7cb62..4295dfc 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1122,76 +1122,70 @@ static void new_asid(struct vcpu_svm *svm, struct svm_cpu_data *sd)
 	svm->vmcb->control.asid = sd->next_asid++;
 }
 
-static unsigned long svm_get_dr(struct kvm_vcpu *vcpu, int dr)
+static int svm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *dest)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
-	unsigned long val;
 
 	switch (dr) {
 	case 0 ... 3:
-		val = vcpu->arch.db[dr];
+		*dest = vcpu->arch.db[dr];
 		break;
+	case 4:
+		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
+			return EMULATE_FAIL; /* will re-inject UD */
+		/* fall through */
 	case 6:
 		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
-			val = vcpu->arch.dr6;
+			*dest = vcpu->arch.dr6;
 		else
-			val = svm->vmcb->save.dr6;
+			*dest = svm->vmcb->save.dr6;
 		break;
+	case 5:
+		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
+			return EMULATE_FAIL; /* will re-inject UD */
+		/* fall through */
 	case 7:
 		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
-			val = vcpu->arch.dr7;
+			*dest = vcpu->arch.dr7;
 		else
-			val = svm->vmcb->save.dr7;
+			*dest = svm->vmcb->save.dr7;
 		break;
-	default:
-		val = 0;
 	}
 
-	return val;
+	return EMULATE_DONE;
 }
 
-static void svm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long value,
-		       int *exception)
+static int svm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long value)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	*exception = 0;
-
 	switch (dr) {
 	case 0 ... 3:
 		vcpu->arch.db[dr] = value;
 		if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
 			vcpu->arch.eff_db[dr] = value;
-		return;
-	case 4 ... 5:
-		if (vcpu->arch.cr4 & X86_CR4_DE)
-			*exception = UD_VECTOR;
-		return;
+		break;
+	case 4:
+		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
+			return EMULATE_FAIL; /* will re-inject UD */
+		/* fall through */
 	case 6:
-		if (value & 0xffffffff00000000ULL) {
-			*exception = GP_VECTOR;
-			return;
-		}
 		vcpu->arch.dr6 = (value & DR6_VOLATILE) | DR6_FIXED_1;
-		return;
+		break;
+	case 5:
+		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
+			return EMULATE_FAIL; /* will re-inject UD */
+		/* fall through */
 	case 7:
-		if (value & 0xffffffff00000000ULL) {
-			*exception = GP_VECTOR;
-			return;
-		}
 		vcpu->arch.dr7 = (value & DR7_VOLATILE) | DR7_FIXED_1;
 		if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)) {
 			svm->vmcb->save.dr7 = vcpu->arch.dr7;
 			vcpu->arch.switch_db_regs = (value & DR7_BP_EN_MASK);
 		}
-		return;
-	default:
-		/* FIXME: Possible case? */
-		printk(KERN_DEBUG "%s: unexpected dr %u\n",
-		       __func__, dr);
-		*exception = UD_VECTOR;
-		return;
+		break;
 	}
+
+	return EMULATE_DONE;
 }
 
 static int pf_interception(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 56a90a6..2b358ba 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3271,29 +3271,14 @@ int emulate_clts(struct kvm_vcpu *vcpu)
 
 int emulator_get_dr(struct x86_emulate_ctxt *ctxt, int dr, unsigned long *dest)
 {
-	struct kvm_vcpu *vcpu = ctxt->vcpu;
-
-	switch (dr) {
-	case 0 ... 3:
-		*dest = kvm_x86_ops->get_dr(vcpu, dr);
-		return X86EMUL_CONTINUE;
-	default:
-		pr_unimpl(vcpu, "%s: unexpected dr %u\n", __func__, dr);
-		return X86EMUL_UNHANDLEABLE;
-	}
+	return kvm_x86_ops->get_dr(ctxt->vcpu, dr, dest);
 }
 
 int emulator_set_dr(struct x86_emulate_ctxt *ctxt, int dr, unsigned long value)
 {
 	unsigned long mask = (ctxt->mode == X86EMUL_MODE_PROT64) ? ~0ULL : ~0U;
-	int exception;
 
-	kvm_x86_ops->set_dr(ctxt->vcpu, dr, value & mask, &exception);
-	if (exception) {
-		/* FIXME: better handling */
-		return X86EMUL_UNHANDLEABLE;
-	}
-	return X86EMUL_CONTINUE;
+	return kvm_x86_ops->set_dr(ctxt->vcpu, dr, value & mask);
 }
 
 void kvm_report_emulation_failure(struct kvm_vcpu *vcpu, const char *context)

[PATCH 5/5] KVM: SVM: Trap all debug register accesses

[Jan Kiszka]

To enable proper debug register emulation under all conditions, trap
access to all DR0..7. This may be optimized later on.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 arch/x86/kvm/svm.c |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 4295dfc..a281368 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -554,13 +554,19 @@ static void init_vmcb(struct vcpu_svm *svm)
 	control->intercept_dr_read = 	INTERCEPT_DR0_MASK |
 					INTERCEPT_DR1_MASK |
 					INTERCEPT_DR2_MASK |
-					INTERCEPT_DR3_MASK;
+					INTERCEPT_DR3_MASK |
+					INTERCEPT_DR4_MASK |
+					INTERCEPT_DR5_MASK |
+					INTERCEPT_DR6_MASK |
+					INTERCEPT_DR7_MASK;
 
 	control->intercept_dr_write = 	INTERCEPT_DR0_MASK |
 					INTERCEPT_DR1_MASK |
 					INTERCEPT_DR2_MASK |
 					INTERCEPT_DR3_MASK |
+					INTERCEPT_DR4_MASK |
 					INTERCEPT_DR5_MASK |
+					INTERCEPT_DR6_MASK |
 					INTERCEPT_DR7_MASK;
 
 	control->intercept_exceptions = (1 << PF_VECTOR) |
@@ -2319,11 +2325,17 @@ static int (*svm_exit_handlers[])(struct vcpu_svm *svm) = {
 	[SVM_EXIT_READ_DR1]			= emulate_on_interception,
 	[SVM_EXIT_READ_DR2]			= emulate_on_interception,
 	[SVM_EXIT_READ_DR3]			= emulate_on_interception,
+	[SVM_EXIT_READ_DR4]			= emulate_on_interception,
+	[SVM_EXIT_READ_DR5]			= emulate_on_interception,
+	[SVM_EXIT_READ_DR6]			= emulate_on_interception,
+	[SVM_EXIT_READ_DR7]			= emulate_on_interception,
 	[SVM_EXIT_WRITE_DR0]			= emulate_on_interception,
 	[SVM_EXIT_WRITE_DR1]			= emulate_on_interception,
 	[SVM_EXIT_WRITE_DR2]			= emulate_on_interception,
 	[SVM_EXIT_WRITE_DR3]			= emulate_on_interception,
+	[SVM_EXIT_WRITE_DR4]			= emulate_on_interception,
 	[SVM_EXIT_WRITE_DR5]			= emulate_on_interception,
+	[SVM_EXIT_WRITE_DR6]			= 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,

[PATCH 3/5] KVM: VMX: Clean up DR6 emulation

[Jan Kiszka]

As we trap all debug register accesses, we do not need to switch real
DR6 at all. Clean up update_exception_bitmap at this chance, too.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 arch/x86/kvm/vmx.c |   23 ++++++-----------------
 1 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 834a8eb..75f1785 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -579,17 +579,12 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
 {
 	u32 eb;
 
-	eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR)
-		| (1u << NM_VECTOR);
-	/*
-	 * Unconditionally intercept #DB so we can maintain dr6 without
-	 * reading it every exit.
-	 */
-	eb |= 1u << DB_VECTOR;
-	if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) {
-		if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
-			eb |= 1u << BP_VECTOR;
-	}
+	eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) |
+	     (1u << NM_VECTOR) | (1u << DB_VECTOR);
+	if ((vcpu->guest_debug &
+	     (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) ==
+	    (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP))
+		eb |= 1u << BP_VECTOR;
 	if (to_vmx(vcpu)->rmode.vm86_active)
 		eb = ~0;
 	if (enable_ept)
@@ -3781,9 +3776,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	 */
 	vmcs_writel(HOST_CR0, read_cr0());
 
-	if (vcpu->arch.switch_db_regs)
-		set_debugreg(vcpu->arch.dr6, 6);
-
 	asm(
 		/* Store host registers */
 		"push %%"R"dx; push %%"R"bp;"
@@ -3884,9 +3876,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 				  | (1 << VCPU_EXREG_PDPTR));
 	vcpu->arch.regs_dirty = 0;
 
-	if (vcpu->arch.switch_db_regs)
-		get_debugreg(vcpu->arch.dr6, 6);
-
 	vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
 	if (vmx->rmode.irq.pending)
 		fixup_rmode_irq(vmx);

Re: [PATCH 0/5] Debug register emulation fixes and optimizations (reloaded)

[Avi Kivity]

On 01/20/2010 07:20 PM, Jan Kiszka wrote:
> Major parts of this series were already posted a while ago during the
> debug register switch optimizations. This version now comes with an
> additional fix for VMX (patch 1) and a rework of mov dr emulation for
> SVM.
>    
Looks good.

-- 
error compiling committee.c: too many arguments to function

Re: [PATCH 0/5] Debug register emulation fixes and optimizations (reloaded)

[Marcelo Tosatti]

On Wed, Jan 20, 2010 at 06:20:20PM +0100, Jan Kiszka wrote:
> Major parts of this series were already posted a while ago during the
> debug register switch optimizations. This version now comes with an
> additional fix for VMX (patch 1) and a rework of mov dr emulation for
> SVM.
> 
> Find this series also at git://git.kiszka.org/linux-kvm.git queues/debugregs
> 
> Jan Kiszka (5):
>       KVM: VMX: Fix exceptions of mov to dr
>       KVM: VMX: Fix emulation of DR4 and DR5
>       KVM: VMX: Clean up DR6 emulation
>       KVM: SVM: Clean up and enhance mov dr emulation
>       KVM: SVM: Trap all debug register accesses
> 
>  arch/x86/include/asm/kvm_host.h |    5 +-
>  arch/x86/kvm/svm.c              |   78 +++++++++++++++++++++------------------
>  arch/x86/kvm/vmx.c              |   67 +++++++++++++++++++--------------
>  arch/x86/kvm/x86.c              |   19 +--------
>  4 files changed, 84 insertions(+), 85 deletions(-)

Applied, thanks.