diff mbox series

[v2,7/9] KVM: SVM: keep DR6 synchronized with vcpu->arch.dr6

Message ID 20200507115011.494562-8-pbonzini@redhat.com (mailing list archive)
State New, archived
Headers show
Series KVM_SET_GUEST_DEBUG tests and fixes, DR accessors cleanups | expand

Commit Message

Paolo Bonzini May 7, 2020, 11:50 a.m. UTC
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), 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>
---
 arch/x86/include/asm/kvm_host.h |  1 -
 arch/x86/kvm/svm/nested.c       | 23 +++++++++++++++--------
 arch/x86/kvm/svm/svm.c          |  9 ++-------
 arch/x86/kvm/vmx/vmx.c          |  6 ------
 arch/x86/kvm/x86.c              |  5 +----
 5 files changed, 18 insertions(+), 26 deletions(-)

Comments

Peter Xu May 7, 2020, 6:22 p.m. UTC | #1
On Thu, May 07, 2020 at 07:50:09AM -0400, Paolo Bonzini wrote:
> @@ -267,7 +268,7 @@ 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;

The rest looks very sane to me, but here I failed to figure out how arch.dr6
finally applied to save.dr6.  I saw it is applied in svm_vcpu_run() in the next
patch, but if that's the case then iiuc this commit may break bisection. Thanks,
Paolo Bonzini May 7, 2020, 10:21 p.m. UTC | #2
On 07/05/20 20:22, Peter Xu wrote:
>> -	svm->vmcb->save.dr6 = nested_vmcb->save.dr6;
>> +	svm->vcpu.arch.dr6  = nested_vmcb->save.dr6;
> The rest looks very sane to me, but here I failed to figure out how arch.dr6
> finally applied to save.dr6.  I saw it is applied in svm_vcpu_run() in the next
> patch, but if that's the case then iiuc this commit may break bisection. Thanks,

You're right, this needs a call to kvm_update_dr6 (which would go away
on the next patch).

Paolo
diff mbox series

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8c247bcb037e..93f6f696d059 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -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);
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index adab5b1c5fe1..1a547e3ac0e5 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -19,6 +19,7 @@ 
 #include <linux/kernel.h>
 
 #include <asm/msr-index.h>
+#include <asm/debugreg.h>
 
 #include "kvm_emulate.h"
 #include "trace.h"
@@ -267,7 +268,7 @@  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;
 	svm->vmcb->save.cpl = nested_vmcb->save.cpl;
 
 	svm->nested.vmcb_msrpm = nested_vmcb->control.msrpm_base_pa & ~0x0fffULL;
@@ -482,7 +483,7 @@  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;
@@ -606,7 +607,7 @@  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 the guest.  */
 	if (svm->vcpu.guest_debug &
@@ -615,22 +616,28 @@  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)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 38f6aeefeb55..f03bffafd9e6 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -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);
@@ -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;
@@ -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;
 	}
@@ -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,
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2384a2dbec44..6153a47109d3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -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)
 {
 }
@@ -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,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f7628555f036..b1b92d904f37 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1129,10 +1129,7 @@  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 */