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    SubjectRe: [PATCH 4/6] hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events
    Frederic Weisbecker wrote:
    [...]
    > @@ -94,6 +87,12 @@ static inline void hw_breakpoint_disable(void)
    > set_debugreg(0UL, 3);
    > }
    >
    > +#ifdef CONFIG_KVM
    > +extern void hw_breakpoint_restore(void);
    > +#else
    > +static inline void hw_breakpoint_restore(void) { }
    > +#endif
    > +

    Hmm, if this shall become a KVM-only API, why the empty wrapper?

    [...]
    > -void arch_flush_thread_hw_breakpoint(struct task_struct *tsk)
    > +#ifdef CONFIG_KVM
    > +void hw_breakpoint_restore(void)
    > {
    > - int i;
    > - struct thread_struct *thread = &(tsk->thread);
    > -
    > - thread->debugreg7 = 0;
    > - for (i = 0; i < HBP_NUM; i++)
    > - thread->debugreg[i] = 0;
    > + set_debugreg(__get_cpu_var(cpu_debugreg[0]), 0);
    > + set_debugreg(__get_cpu_var(cpu_debugreg[1]), 1);
    > + set_debugreg(__get_cpu_var(cpu_debugreg[2]), 2);
    > + set_debugreg(__get_cpu_var(cpu_debugreg[3]), 3);
    > + set_debugreg(current->thread.debugreg6, 6);
    > + set_debugreg(__get_cpu_var(dr7), 7);
    > }
    > +#endif

    EXPORT_SYMBOL_GPL(hw_breakpoint_restore);

    as KVM can be built as module.

    [...]
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index fc2974a..32d7bca 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -42,6 +42,7 @@
    > #define CREATE_TRACE_POINTS
    > #include "trace.h"
    >
    > +#include <asm/debugreg.h>
    > #include <asm/uaccess.h>
    > #include <asm/msr.h>
    > #include <asm/desc.h>
    > @@ -3643,14 +3644,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
    > trace_kvm_entry(vcpu->vcpu_id);
    > kvm_x86_ops->run(vcpu, kvm_run);
    >
    > - if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) {
    > - set_debugreg(current->thread.debugreg[0], 0);
    > - set_debugreg(current->thread.debugreg[1], 1);
    > - set_debugreg(current->thread.debugreg[2], 2);
    > - set_debugreg(current->thread.debugreg[3], 3);
    > - set_debugreg(current->thread.debugreg6, 6);
    > - set_debugreg(current->thread.debugreg7, 7);
    > - }
    > + if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG)))
    > + hw_breakpoint_restore();

    TIF_DEBUG is only set on active ptrace hw-breakpoints, thus we miss
    other types here, right? (Note: arch.switch_db_regs is guest-related,
    thus does not help in this regard.)

    Jan

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