Re: [PATCH 5/5] KVM: x86: BSP in MSR_IA32_APICBASE is writable

From: Nadav Amit <nadav.amit@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Nadav Amit <namit@cs.technion.ac.il>,
	mtosatti@redhat.com, kvm@vger.kernel.org
Subject: Re: [PATCH 5/5] KVM: x86: BSP in MSR_IA32_APICBASE is writable
Date: Mon, 30 Mar 2015 22:31:18 +0300	[thread overview]
Message-ID: <68F69D11-D45C-497D-B51B-9D85BA2F5891@gmail.com> (raw)
In-Reply-To: <55196188.3020804@redhat.com>

Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 30/03/2015 16:40, Nadav Amit wrote:
>> Paolo,
>> 
>> It appears you are right and I have not tested 4 and 5 well enough. I’ll
>> repost them (the others were tested presumably well enough).
>> 
>> Two short questions:
>> Can I use init.c in the kvm-unit-tests ? 
>> Why is it disabled?
> 
> Because QEMU support for INIT is incomplete, so the tests would fail
> ("Uh, hard reset!").  IIRC sending init to BSP with APIC_DEST_SELF is
> also not supported by actual hardware (or at least not supported
> "officially") so that test would also have to be changed to not use a
> shortcut.

So, I would revive the init unit-test and disable the failing assertions,
right?

BTW: It appears that there is another bug - DR[0..3] are not reloaded after
reset.

Regards,
Nadav

-- >8 --

From: Nadav Amit <namit@cs.technion.ac.il>
Subject: [PATCH] KVM: x86: DR0-DR3 are not clear on reset

DR0-DR3 are not cleared as they should during reset and when they are set from
userspace.  It appears to be caused by c77fb5fe6f03 ("KVM: x86: Allow the guest
to run with dirty debug registers").

Force their reload on these situations.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/x86.c              | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index bf5a160..913ae41 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -345,6 +345,7 @@ struct kvm_pmu {
 enum {
 	KVM_DEBUGREG_BP_ENABLED = 1,
 	KVM_DEBUGREG_WONT_EXIT = 2,
+	KVM_DEBUGREG_RELOAD = 4,
 };
 
 struct kvm_vcpu_arch {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cc2c759..1f65c3a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -801,6 +801,17 @@ unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_get_cr8);
 
+static void kvm_update_dr0123(struct kvm_vcpu *vcpu)
+{
+	int i;
+
+	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)) {
+		for (i = 0; i < KVM_NR_DB_REGS; i++)
+			vcpu->arch.eff_db[i] = vcpu->arch.db[i];
+		vcpu->arch.switch_db_regs |= KVM_DEBUGREG_RELOAD;
+	}
+}
+
 static void kvm_update_dr6(struct kvm_vcpu *vcpu)
 {
 	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
@@ -3150,6 +3161,7 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 		return -EINVAL;
 
 	memcpy(vcpu->arch.db, dbgregs->db, sizeof(vcpu->arch.db));
+	kvm_update_dr0123(vcpu);
 	vcpu->arch.dr6 = dbgregs->dr6;
 	kvm_update_dr6(vcpu);
 	vcpu->arch.dr7 = dbgregs->dr7;
@@ -6322,6 +6334,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		set_debugreg(vcpu->arch.eff_db[2], 2);
 		set_debugreg(vcpu->arch.eff_db[3], 3);
 		set_debugreg(vcpu->arch.dr6, 6);
+		vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD;
 	}
 
 	trace_kvm_entry(vcpu->vcpu_id);
@@ -7096,6 +7109,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu)
 	kvm_clear_exception_queue(vcpu);
 
 	memset(vcpu->arch.db, 0, sizeof(vcpu->arch.db));
+	kvm_update_dr0123(vcpu);
 	vcpu->arch.dr6 = DR6_INIT;
 	kvm_update_dr6(vcpu);
 	vcpu->arch.dr7 = DR7_FIXED_1;
-- 
1.9.1

