linux-kernel - Re: [PATCH v2 13/16] powerpc/watchpoint: Prepare handler to handle more than one watcnhpoint

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Message-ID: <6b89991b-481a-8cbd-b5b7-559e5e16cf92@c-s.fr>
Date:   Wed, 1 Apr 2020 08:50:01 +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 13/16] powerpc/watchpoint: Prepare handler to handle
 more than one watcnhpoint



Le 01/04/2020 à 08:13, Ravi Bangoria a écrit :
> Currently we assume that we have only one watchpoint supported by hw.
> Get rid of that assumption and use dynamic loop instead. This should
> make supporting more watchpoints very easy.
> 
> With more than one watchpoint, exception handler need to know which
> DAWR caused the exception, and hw currently does not provide it. So
> we need sw logic for the same. To figure out which DAWR caused the
> exception, check all different combinations of user specified range,
> dawr address range, actual access range and dawrx constrains. For ex,
> if user specified range and actual access range overlaps but dawrx is
> configured for readonly watchpoint and the instruction is store, this
> DAWR must not have caused exception.
> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/processor.h |   2 +-
>   arch/powerpc/include/asm/sstep.h     |   2 +
>   arch/powerpc/kernel/hw_breakpoint.c  | 396 +++++++++++++++++++++------
>   arch/powerpc/kernel/process.c        |   3 -
>   4 files changed, 313 insertions(+), 90 deletions(-)
> 

[...]

> -static bool
> -dar_range_overlaps(unsigned long dar, int size, struct arch_hw_breakpoint *info)
> +static bool dar_user_range_overlaps(unsigned long dar, int size,
> +				    struct arch_hw_breakpoint *info)
>   {
>   	return ((dar <= info->address + info->len - 1) &&
>   		(dar + size - 1 >= info->address));
>   }

Here and several other places, I think it would be more clear if you 
could avoid the - 1 :

	return ((dar < info->address + info->len) &&
		(dar + size > info->address));


>   
> +static bool dar_in_hw_range(unsigned long dar, struct arch_hw_breakpoint *info)
> +{
> +	unsigned long hw_start_addr, hw_end_addr;
> +
> +	hw_start_addr = ALIGN_DOWN(info->address, HW_BREAKPOINT_SIZE);
> +	hw_end_addr = ALIGN(info->address + info->len, HW_BREAKPOINT_SIZE) - 1;
> +
> +	return ((hw_start_addr <= dar) && (hw_end_addr >= dar));
> +}

	hw_end_addr = ALIGN(info->address + info->len, HW_BREAKPOINT_SIZE);

	return ((hw_start_addr <= dar) && (hw_end_addr > dar));

Christophe

> +
> +static bool dar_hw_range_overlaps(unsigned long dar, int size,
> +				  struct arch_hw_breakpoint *info)
> +{
> +	unsigned long hw_start_addr, hw_end_addr;
> +
> +	hw_start_addr = ALIGN_DOWN(info->address, HW_BREAKPOINT_SIZE);
> +	hw_end_addr = ALIGN(info->address + info->len, HW_BREAKPOINT_SIZE) - 1;
> +
> +	return ((dar <= hw_end_addr) && (dar + size - 1 >= hw_start_addr));
> +}

Same

Christophe