KVM: x86: Drop kvm_x86_ops.set_dr6() in favor of a new KVM_RUN flag

[ Upstream commit 80c64c7afea1da6a93ebe88d3d29d8a60377ef80 ]

Instruct vendor code to load the guest's DR6 into hardware via a new
KVM_RUN flag, and remove kvm_x86_ops.set_dr6(), whose sole purpose was to
load vcpu->arch.dr6 into hardware when DR6 can be read/written directly
by the guest.

Note, TDX already WARNs on any run_flag being set, i.e. will yell if KVM
thinks DR6 needs to be reloaded.  TDX vCPUs force KVM_DEBUGREG_AUTO_SWITCH
and never clear the flag, i.e. should never observe KVM_RUN_LOAD_GUEST_DR6.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250610232010.162191-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
[sean: drop TDX changes]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index cfb22f8c451a7fe16e6d19f8d5fe3742a5e6232f..861d080ed4c6abc97e9f60a486d6d1ce3f9a9b44 100644 (file)
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -47,7 +47,6 @@ KVM_X86_OP(set_idt)
 KVM_X86_OP(get_gdt)
 KVM_X86_OP(set_gdt)
 KVM_X86_OP(sync_dirty_debug_regs)
-KVM_X86_OP(set_dr6)
 KVM_X86_OP(set_dr7)
 KVM_X86_OP(cache_reg)
 KVM_X86_OP(get_rflags)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index cccc8cbe72db959f0f3b9eae3e47e68203aefcee..2ed05925d9d5bbcebf721986ca60e9ce5eb37368 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1629,6 +1629,7 @@ static inline u16 kvm_lapic_irq_dest_mode(bool dest_mode_logical)
 
 enum kvm_x86_run_flags {
        KVM_RUN_FORCE_IMMEDIATE_EXIT    = BIT(0),
+       KVM_RUN_LOAD_GUEST_DR6          = BIT(1),
 };
 
 struct kvm_x86_ops {
@@ -1679,7 +1680,6 @@ struct kvm_x86_ops {
        void (*get_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
        void (*set_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
        void (*sync_dirty_debug_regs)(struct kvm_vcpu *vcpu);
-       void (*set_dr6)(struct kvm_vcpu *vcpu, unsigned long value);
        void (*set_dr7)(struct kvm_vcpu *vcpu, unsigned long value);
        void (*cache_reg)(struct kvm_vcpu *vcpu, enum kvm_reg reg);
        unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7d1b871cfc02d357b03f60ab1a0771cf12bb250c..800f781475c0287b83ed5b36ceac496c957c0cd8 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4270,10 +4270,13 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
        svm_hv_update_vp_id(svm->vmcb, vcpu);
 
        /*
-        * Run with all-zero DR6 unless needed, so that we can get the exact cause
-        * of a #DB.
+        * Run with all-zero DR6 unless the guest can write DR6 freely, so that
+        * KVM can get the exact cause of a #DB.  Note, loading guest DR6 from
+        * KVM's snapshot is only necessary when DR accesses won't exit.
         */
-       if (likely(!(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)))
+       if (unlikely(run_flags & KVM_RUN_LOAD_GUEST_DR6))
+               svm_set_dr6(vcpu, vcpu->arch.dr6);
+       else if (likely(!(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)))
                svm_set_dr6(vcpu, DR6_ACTIVE_LOW);
 
        clgi();
@@ -5084,7 +5087,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
        .set_idt = svm_set_idt,
        .get_gdt = svm_get_gdt,
        .set_gdt = svm_set_gdt,
-       .set_dr6 = svm_set_dr6,
        .set_dr7 = svm_set_dr7,
        .sync_dirty_debug_regs = svm_sync_dirty_debug_regs,
        .cache_reg = svm_cache_reg,

diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index 47476fcc179a5265805fa1f251db7166a5bf2777..7668e2fb8043ef96182f85a7f7ac45a35cd2db05 100644 (file)
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -60,7 +60,6 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
        .set_idt = vmx_set_idt,
        .get_gdt = vmx_get_gdt,
        .set_gdt = vmx_set_gdt,
-       .set_dr6 = vmx_set_dr6,
        .set_dr7 = vmx_set_dr7,
        .sync_dirty_debug_regs = vmx_sync_dirty_debug_regs,
        .cache_reg = vmx_cache_reg,

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2a977cdfcd0c126ec616ba83a79cc56a52b5e64e..b9c7940feac6baf5fc8a0f9bd62d521815118275 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5630,12 +5630,6 @@ void vmx_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)
        set_debugreg(DR6_RESERVED, 6);
 }
 
-void vmx_set_dr6(struct kvm_vcpu *vcpu, unsigned long val)
-{
-       lockdep_assert_irqs_disabled();
-       set_debugreg(vcpu->arch.dr6, 6);
-}
-
 void vmx_set_dr7(struct kvm_vcpu *vcpu, unsigned long val)
 {
        vmcs_writel(GUEST_DR7, val);
@@ -7400,6 +7394,9 @@ fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
                vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
        vcpu->arch.regs_dirty = 0;
 
+       if (run_flags & KVM_RUN_LOAD_GUEST_DR6)
+               set_debugreg(vcpu->arch.dr6, 6);
+
        /*
         * Refresh vmcs.HOST_CR3 if necessary.  This must be done immediately
         * prior to VM-Enter, as the kernel may load a new ASID (PCID) any time

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 44ab46f2a2d2ba8329a0e2869cc7be8299c6384e..7beea8fb6ea6431bde560ce05c5e27f31f342356 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10977,7 +10977,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
                set_debugreg(vcpu->arch.eff_db[3], 3);
                /* When KVM_DEBUGREG_WONT_EXIT, dr6 is accessible in guest. */
                if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT))
-                       kvm_x86_call(set_dr6)(vcpu, vcpu->arch.dr6);
+                       run_flags |= KVM_RUN_LOAD_GUEST_DR6;
        } else if (unlikely(hw_breakpoint_active())) {
                set_debugreg(DR7_FIXED_1, 7);
        }