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

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Message-ID: <48ef25ff-0d06-54d9-b467-ff068465e3dc@arm.com>
Date:   Thu, 17 Sep 2020 15:24:39 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.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 9/17/20 3:03 PM, Catalin Marinas wrote:
> 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).
>

Ok, I will fix it in the next version.

>> +
>> +	/*
>> +	 * 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 ;).
> 

All right, will change it ;)

>> +	 * 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.
> 

Ok, thanks.

-- 
Regards,
Vincenzo