linux-kernel - [RFC PATCH 29/67] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior

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Message-Id: <df78c741300046037935c0f7ae763e302e66f639.1605232743.git.isaku.yamahata@intel.com>
Date:   Mon, 16 Nov 2020 10:26:14 -0800
From:   isaku.yamahata@...el.com
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     isaku.yamahata@...el.com, isaku.yamahata@...il.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: [RFC PATCH 29/67] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior

From: Sean Christopherson <sean.j.christopherson@...el.com>

Add a flag, KVM_DEBUGREG_AUTO_SWITCHED, to skip saving/restoring DRs
irrespective of any other flags.  TDX-SEAM unconditionally saves and
restores host DRs, ergo there is nothing to do.

Opportunistically convert the KVM_DEBUGREG_* definitions to use BIT().

Reported-by: Xiaoyao Li <xiaoyao.li@...el.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/include/asm/kvm_host.h | 7 ++++---
 arch/x86/kvm/x86.c              | 6 ++++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a6c89666ec49..815469875445 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -464,9 +464,10 @@ struct kvm_pmu {
 struct kvm_pmu_ops;
 
 enum {
-	KVM_DEBUGREG_BP_ENABLED = 1,
-	KVM_DEBUGREG_WONT_EXIT = 2,
-	KVM_DEBUGREG_RELOAD = 4,
+	KVM_DEBUGREG_BP_ENABLED 	= BIT(0),
+	KVM_DEBUGREG_WONT_EXIT		= BIT(1),
+	KVM_DEBUGREG_RELOAD		= BIT(2),
+	KVM_DEBUGREG_AUTO_SWITCHED	= BIT(3),
 };
 
 struct kvm_mtrr_range {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 42bd24ba7fdd..098888edc3ad 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9009,7 +9009,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
 
-	if (unlikely(vcpu->arch.switch_db_regs)) {
+	if (unlikely(vcpu->arch.switch_db_regs & ~KVM_DEBUGREG_AUTO_SWITCHED)) {
 		set_debugreg(0, 7);
 		set_debugreg(vcpu->arch.eff_db[0], 0);
 		set_debugreg(vcpu->arch.eff_db[1], 1);
@@ -9029,6 +9029,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	 */
 	if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)) {
 		WARN_ON(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP);
+		WARN_ON(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCHED);
 		kvm_x86_ops.sync_dirty_debug_regs(vcpu);
 		kvm_update_dr0123(vcpu);
 		kvm_update_dr7(vcpu);
@@ -9042,7 +9043,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	 * care about the messed up debug address registers. But if
 	 * we have some of them active, restore the old state.
 	 */
-	if (hw_breakpoint_active())
+	if (hw_breakpoint_active() &&
+	    !(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCHED))
 		hw_breakpoint_restore();
 
 	vcpu->arch.last_vmentry_cpu = vcpu->cpu;
-- 
2.17.1