linux-kernel - Re: [PATCH V2 3/4] arm64/mm: Consolidate page fault information capture

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Message-ID: <20190604144209.GJ6610@arrakis.emea.arm.com>
Date:   Tue, 4 Jun 2019 15:42:09 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH V2 3/4] arm64/mm: Consolidate page fault information
 capture

On Mon, Jun 03, 2019 at 12:11:24PM +0530, Anshuman Khandual wrote:
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index da02678..4bb65f3 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -435,6 +435,14 @@ static bool is_el0_instruction_abort(unsigned int esr)
>  	return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_LOW;
>  }
>  
> +/*
> + * This is applicable only for EL0 write aborts.
> + */
> +static bool is_el0_write_abort(unsigned int esr)
> +{
> +	return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM);
> +}

What makes this EL0 only?

> +
>  static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
>  				   struct pt_regs *regs)
>  {
> @@ -443,6 +451,9 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
>  	vm_fault_t fault, major = 0;
>  	unsigned long vm_flags = VM_READ | VM_WRITE;
>  	unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
> +	bool is_user = user_mode(regs);
> +	bool is_el0_exec = is_el0_instruction_abort(esr);
> +	bool is_el0_write = is_el0_write_abort(esr);
>  
>  	if (notify_page_fault(regs, esr))
>  		return 0;
> @@ -454,12 +465,12 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
>  	if (faulthandler_disabled() || !mm)
>  		goto no_context;
>  
> -	if (user_mode(regs))
> +	if (is_user)
>  		mm_flags |= FAULT_FLAG_USER;
>  
> -	if (is_el0_instruction_abort(esr)) {
> +	if (is_el0_exec) {
>  		vm_flags = VM_EXEC;
> -	} else if ((esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM)) {
> +	} else if (is_el0_write) {
>  		vm_flags = VM_WRITE;
>  		mm_flags |= FAULT_FLAG_WRITE;
>  	}

This can be triggered by an EL1 write to a user mapping, so is_el0_write
is misleading.

-- 
Catalin