linux-kernel - [PATCH 1/2] KVM: x86: handle hardware breakpoints during emulation

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Message-Id: <1369929631-2101-2-git-send-email-pbonzini@redhat.com>
Date:	Thu, 30 May 2013 18:00:30 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, gnatapov@...hat.com, jan.kiszka@...mens.com
Subject: [PATCH 1/2] KVM: x86: handle hardware breakpoints during emulation

This lets debugging work better during emulation of invalid
guest state.

The check is done before emulating the instruction, and (in the case
of guest debugging) reuses EMULATE_DO_MMIO to exit with KVM_EXIT_DEBUG.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/include/asm/kvm_host.h |  3 +-
 arch/x86/kvm/x86.c              | 65 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e2e09f3..aefd8c2 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -788,9 +788,10 @@ extern u32  kvm_min_guest_tsc_khz;
 extern u32  kvm_max_guest_tsc_khz;
 
 enum emulation_result {
-	EMULATE_DONE,       /* no further processing */
-	EMULATE_DO_MMIO,      /* kvm_run filled with mmio request */
+	EMULATE_DONE,         /* no further processing */
+	EMULATE_DO_MMIO,      /* kvm_run ready for userspace exit */
 	EMULATE_FAIL,         /* can't emulate this instruction */
+	EMULATE_PROCEED,      /* proceed with rest of emulation */
 };
 
 #define EMULTYPE_NO_DECODE	    (1 << 0)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1d928af..33b51bc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4872,6 +4872,60 @@ static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
 static int complete_emulated_mmio(struct kvm_vcpu *vcpu);
 static int complete_emulated_pio(struct kvm_vcpu *vcpu);
 
+static int kvm_vcpu_check_hw_bp(unsigned long addr, u32 type, u32 dr7,
+				unsigned long *db)
+{
+	u32 dr6 = 0;
+	int i;
+	u32 enable, rwlen;
+
+	enable = dr7;
+	rwlen = dr7 >> 16;
+	for (i = 0; i < 4; i++, enable >>= 2, rwlen >>= 4)
+		if ((enable & 3) && (rwlen & 15) == type && db[i] == addr)
+			dr6 |= (1 << i);
+	return dr6;
+}
+
+static int kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu)
+{
+	struct kvm_run *kvm_run = vcpu->run;
+	unsigned long eip = vcpu->arch.emulate_ctxt.eip;
+	u32 dr6 = 0;
+
+	if (unlikely(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) &&
+	    (vcpu->arch.guest_debug_dr7 & DR7_BP_EN_MASK)) {
+		dr6 = kvm_vcpu_check_hw_bp(eip, 0,
+					   vcpu->arch.guest_debug_dr7,
+					   vcpu->arch.eff_db);
+
+		if (dr6 != 0) {
+			kvm_run->debug.arch.dr6 = dr6 | DR6_FIXED_1;
+			kvm_run->debug.arch.pc = kvm_rip_read(vcpu) +
+				get_segment_base(vcpu, VCPU_SREG_CS);
+
+			kvm_run->debug.arch.exception = DB_VECTOR;
+			kvm_run->exit_reason = KVM_EXIT_DEBUG;
+			return EMULATE_DO_MMIO;
+		}
+	}
+
+	if (unlikely(vcpu->arch.dr7 & DR7_BP_EN_MASK)) {
+		dr6 = kvm_vcpu_check_hw_bp(eip, 0,
+					   vcpu->arch.dr7,
+					   vcpu->arch.db);
+
+		if (dr6 != 0) {
+			vcpu->arch.dr6 &= ~15;
+			vcpu->arch.dr6 |= dr6;
+			kvm_queue_exception(vcpu, DB_VECTOR);
+			return EMULATE_DONE;
+		}
+	}
+
+	return EMULATE_PROCEED;
+}
+
 int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 			    unsigned long cr2,
 			    int emulation_type,
@@ -4892,6 +4946,17 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 
 	if (!(emulation_type & EMULTYPE_NO_DECODE)) {
 		init_emulate_ctxt(vcpu);
+
+		/*
+		 * We will reenter on the same instruction since
+		 * we do not set complete_userspace_io.  This does not
+		 * handle watchpoints yet, those would be handled in
+		 * the emulate_ops.
+		 */
+		r = kvm_vcpu_check_breakpoint(vcpu);
+		if (r != EMULATE_PROCEED)
+			return r;
+
 		ctxt->interruptibility = 0;
 		ctxt->have_exception = false;
 		ctxt->perm_ok = false;
-- 
1.8.1.4


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