linux-kernel - Re: [PATCH v2 24/37] arm64: mte: Add in-kernel tag fault handler

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Date:   Thu, 17 Sep 2020 15:03:37 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        kasan-dev@...glegroups.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 24/37] arm64: mte: Add in-kernel tag fault handler

On Tue, Sep 15, 2020 at 11:16:06PM +0200, Andrey Konovalov wrote:
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index a3bd189602df..cdc23662691c 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -294,6 +295,18 @@ static void die_kernel_fault(const char *msg, unsigned long addr,
>  	do_exit(SIGKILL);
>  }
>  
> +static void report_tag_fault(unsigned long addr, unsigned int esr,
> +			     struct pt_regs *regs)
> +{
> +	bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> +
> +	pr_alert("Memory Tagging Extension Fault in %pS\n", (void *)regs->pc);
> +	pr_alert("  %s at address %lx\n", is_write ? "Write" : "Read", addr);
> +	pr_alert("  Pointer tag: [%02x], memory tag: [%02x]\n",
> +			mte_get_ptr_tag(addr),
> +			mte_get_mem_tag((void *)addr));
> +}
> +
>  static void __do_kernel_fault(unsigned long addr, unsigned int esr,
>  			      struct pt_regs *regs)
>  {
> @@ -641,10 +654,31 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
>  	return 0;
>  }
>  
> +static void do_tag_recovery(unsigned long addr, unsigned int esr,
> +			   struct pt_regs *regs)
> +{
> +	report_tag_fault(addr, esr, regs);

I'd only report this once since we expect it to be disabled lazily on
the other CPUs (i.e. just use a "static bool reported" to keep track).

> +
> +	/*
> +	 * Disable Memory Tagging Extension Tag Checking on the local CPU

Too verbose, just say MTE tag checking, people reading this code should
have learnt already what MTE stands for ;).

> +	 * for the current EL.
> +	 * It will be done lazily on the other CPUs when they will hit a
> +	 * tag fault.
> +	 */
> +	sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_NONE);
> +	isb();
> +}
> +
> +
>  static int do_tag_check_fault(unsigned long addr, unsigned int esr,
>  			      struct pt_regs *regs)
>  {
> -	do_bad_area(addr, esr, regs);
> +	/* The tag check fault (TCF) is per TTBR */
> +	if (is_ttbr0_addr(addr))
> +		do_bad_area(addr, esr, regs);
> +	else
> +		do_tag_recovery(addr, esr, regs);

This part looks fine now.

-- 
Catalin