linux-kernel - Re: [PATCH v2 14/16] powerpc/watchpoint: Don't allow concurrent perf and ptrace events

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Date:   Wed, 1 Apr 2020 08:52:16 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>, mpe@...erman.id.au,
        mikey@...ling.org
Cc:     apopple@...ux.ibm.com, paulus@...ba.org, npiggin@...il.com,
        naveen.n.rao@...ux.vnet.ibm.com, peterz@...radead.org,
        jolsa@...nel.org, oleg@...hat.com, fweisbec@...il.com,
        mingo@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 14/16] powerpc/watchpoint: Don't allow concurrent perf
 and ptrace events



Le 01/04/2020 à 08:13, Ravi Bangoria a écrit :
> With Book3s DAWR, ptrace and perf watchpoints on powerpc behaves
> differently. Ptrace watchpoint works in one-shot mode and generates
> signal before executing instruction. It's ptrace user's job to
> single-step the instruction and re-enable the watchpoint. OTOH, in
> case of perf watchpoint, kernel emulates/single-steps the instruction
> and then generates event. If perf and ptrace creates two events with
> same or overlapping address ranges, it's ambiguous to decide who
> should single-step the instruction. Because of this issue, don't
> allow perf and ptrace watchpoint at the same time if their address
> range overlaps.
> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/hw_breakpoint.h |   2 +
>   arch/powerpc/kernel/hw_breakpoint.c      | 222 +++++++++++++++++++++++
>   kernel/events/hw_breakpoint.c            |  16 ++
>   3 files changed, 240 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
> index abc4603c0efe..9d3bd1169591 100644
> --- a/arch/powerpc/include/asm/hw_breakpoint.h
> +++ b/arch/powerpc/include/asm/hw_breakpoint.h
> @@ -70,6 +70,8 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
>   						unsigned long val, void *data);
>   int arch_install_hw_breakpoint(struct perf_event *bp);
>   void arch_uninstall_hw_breakpoint(struct perf_event *bp);
> +int arch_reserve_bp_slot(struct perf_event *bp);
> +void arch_release_bp_slot(struct perf_event *bp);
>   void arch_unregister_hw_breakpoint(struct perf_event *bp);
>   void hw_breakpoint_pmu_read(struct perf_event *bp);
>   extern void flush_ptrace_hw_breakpoint(struct task_struct *tsk);
> diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
> index 07a6cdea84ed..f813acb0d9f0 100644
> --- a/arch/powerpc/kernel/hw_breakpoint.c
> +++ b/arch/powerpc/kernel/hw_breakpoint.c
> @@ -123,6 +123,228 @@ static bool is_ptrace_bp(struct perf_event *bp)
>   	return bp->overflow_handler == ptrace_triggered;
>   }
>   
> +struct breakpoint {
> +	struct list_head list;
> +	struct perf_event *bp;
> +	bool ptrace_bp;
> +};
> +
> +static DEFINE_PER_CPU(struct breakpoint *, cpu_bps[HBP_NUM_MAX]);
> +static LIST_HEAD(task_bps);
> +
> +static struct breakpoint *alloc_breakpoint(struct perf_event *bp)
> +{
> +	struct breakpoint *tmp;
> +
> +	tmp = kzalloc(sizeof(*tmp), GFP_KERNEL);
> +	if (!tmp)
> +		return ERR_PTR(-ENOMEM);
> +	tmp->bp = bp;
> +	tmp->ptrace_bp = is_ptrace_bp(bp);
> +	return tmp;
> +}
> +
> +static bool bp_addr_range_overlap(struct perf_event *bp1, struct perf_event *bp2)
> +{
> +	__u64 bp1_saddr, bp1_eaddr, bp2_saddr, bp2_eaddr;
> +
> +	bp1_saddr = ALIGN_DOWN(bp1->attr.bp_addr, HW_BREAKPOINT_SIZE);
> +	bp1_eaddr = ALIGN(bp1->attr.bp_addr + bp1->attr.bp_len, HW_BREAKPOINT_SIZE) - 1;
> +	bp2_saddr = ALIGN_DOWN(bp2->attr.bp_addr, HW_BREAKPOINT_SIZE);
> +	bp2_eaddr = ALIGN(bp2->attr.bp_addr + bp2->attr.bp_len, HW_BREAKPOINT_SIZE) - 1;
> +
> +	return (bp1_saddr <= bp2_eaddr && bp1_eaddr >= bp2_saddr);

Could avoid the - 1 on bp1_eaddr and bp2_eaddr by doing:

	return (bp1_saddr < bp2_eaddr && bp1_eaddr > bp2_saddr);


Christophe