From 375e28ffc0cf4fc48862c03994ec4a93254cf1c6 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 10 Aug 2021 06:07:06 -0400 Subject: KVM: X86: Set host DR6 only on VMX and for KVM_DEBUGREG_WONT_EXIT Commit c77fb5fe6f03 ("KVM: x86: Allow the guest to run with dirty debug registers") allows the guest accessing to DRs without exiting when KVM_DEBUGREG_WONT_EXIT and we need to ensure that they are synchronized on entry to the guest---including DR6 that was not synced before the commit. But the commit sets the hardware DR6 not only when KVM_DEBUGREG_WONT_EXIT, but also when KVM_DEBUGREG_BP_ENABLED. The second case is unnecessary and just leads to a more case which leaks stale DR6 to the host which has to be resolved by unconditionally reseting DR6 in kvm_arch_vcpu_put(). Even if KVM_DEBUGREG_WONT_EXIT, however, setting the host DR6 only matters on VMX because SVM always uses the DR6 value from the VMCB. So move this line to vmx.c and make it conditional on KVM_DEBUGREG_WONT_EXIT. Reported-by: Lai Jiangshan Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/vmx.c | 4 ++++ arch/x86/kvm/x86.c | 1 - 2 files changed, 4 insertions(+), 1 deletion(-) (limited to 'arch/x86') diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index ae8e62df16dd..7c1c8ef1a286 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6625,6 +6625,10 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu) vmx->loaded_vmcs->host_state.cr4 = cr4; } + /* When KVM_DEBUGREG_WONT_EXIT, dr6 is accessible in guest. */ + if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)) + set_debugreg(vcpu->arch.dr6, 6); + /* When single-stepping over STI and MOV SS, we must clear the * corresponding interruptibility bits in the guest state. Otherwise * vmentry fails as it then expects bit 14 (BS) in pending debug diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index eca5f005a7fc..15ac8645e532 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9602,7 +9602,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) set_debugreg(vcpu->arch.eff_db[1], 1); set_debugreg(vcpu->arch.eff_db[2], 2); set_debugreg(vcpu->arch.eff_db[3], 3); - set_debugreg(vcpu->arch.dr6, 6); } else if (unlikely(hw_breakpoint_active())) { set_debugreg(0, 7); } -- cgit