The patch below does not apply to the 6.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.15.y git checkout FETCH_HEAD git cherry-pick -x 80c64c7afea1da6a93ebe88d3d29d8a60377ef80 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025081242-polygon-exploring-2a87@gregkh' --subject-prefix 'PATCH 6.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 80c64c7afea1da6a93ebe88d3d29d8a60377ef80 Mon Sep 17 00:00:00 2001 From: Sean Christopherson seanjc@google.com Date: Tue, 10 Jun 2025 16:20:05 -0700 Subject: [PATCH] KVM: x86: Drop kvm_x86_ops.set_dr6() in favor of a new KVM_RUN flag

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

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h index 8d50e3e0a19b..9e0c37ea267e 100644 --- a/arch/x86/include/asm/kvm-x86-ops.h +++ b/arch/x86/include/asm/kvm-x86-ops.h @@ -49,7 +49,6 @@ 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 8d81684fa15d..4f7ee2dbf10e 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1676,6 +1676,7 @@ 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 { @@ -1728,7 +1729,6 @@ 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 83d1b62130b1..be8c43049f4d 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -4438,10 +4438,13 @@ 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(); @@ -5252,7 +5255,6 @@ 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 fef3e3803707..c85cbce6d2f6 100644 --- a/arch/x86/kvm/vmx/main.c +++ b/arch/x86/kvm/vmx/main.c @@ -489,14 +489,6 @@ static void vt_set_gdt(struct kvm_vcpu *vcpu, struct desc_ptr *dt) vmx_set_gdt(vcpu, dt); }

-static void vt_set_dr6(struct kvm_vcpu *vcpu, unsigned long val) -{ - if (is_td_vcpu(vcpu)) - return; - - vmx_set_dr6(vcpu, val); -} - static void vt_set_dr7(struct kvm_vcpu *vcpu, unsigned long val) { if (is_td_vcpu(vcpu)) @@ -943,7 +935,6 @@ struct kvm_x86_ops vt_x86_ops __initdata = { .set_idt = vt_op(set_idt), .get_gdt = vt_op(get_gdt), .set_gdt = vt_op(set_gdt), - .set_dr6 = vt_op(set_dr6), .set_dr7 = vt_op(set_dr7), .sync_dirty_debug_regs = vt_op(sync_dirty_debug_regs), .cache_reg = vt_op(cache_reg), diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index a61a28944de6..4ee6cc796855 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -5606,12 +5606,6 @@ 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); @@ -7370,6 +7364,9 @@ 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 07ff02eed399..7fe3549bbd93 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11046,7 +11046,7 @@ 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(0, 7); }