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

From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
	Andrey Konovalov <andreyknvl@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>,
	kasan-dev@googlegroups.com,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Alexander Potapenko <glider@google.com>,
	Marco Elver <elver@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Elena Petrova <lenaptr@google.com>,
	Branislav Rankov <Branislav.Rankov@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 24/37] arm64: mte: Add in-kernel tag fault handler
Date: Thu, 17 Sep 2020 15:24:39 +0100	[thread overview]
Message-ID: <48ef25ff-0d06-54d9-b467-ff068465e3dc@arm.com> (raw)
In-Reply-To: <20200917140337.GC10662@gaia>

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