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Message-ID: <7f4729cd-da86-4198-a2be-1c12a5513eb3@intel.com>
Date: Tue, 23 Jan 2024 11:28:26 -0800
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] x86/mm: Simplify redundant overlap calculation
Content-Language: en-US
To: Dave Hansen <dave.hansen@linux.intel.com>, <linux-kernel@vger.kernel.org>
CC: David Binderman <dcb314@hotmail.com>, Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	<x86@kernel.org>
References: <20240123163623.1342917-1-dave.hansen@linux.intel.com>
From: Sohil Mehta <sohil.mehta@intel.com>
In-Reply-To: <20240123163623.1342917-1-dave.hansen@linux.intel.com>
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On 1/23/2024 8:36 AM, Dave Hansen wrote:
> There have been a couple of reports that the two sides of the
> overlaps() calculation are redundant.  I spent way too much time
> looking at this, but I became convinced that they are redundant
> when a little test program of mine produced identical disassembly
> for both versions of the check.
> 
> Remove the second condition.  It is exactly the same as the first.
> 
> Fixes: 91ee8f5c1f50 ("x86/mm/cpa: Allow range check for static protections")
> Reported-by: David Binderman <dcb314@hotmail.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: x86@kernel.org
> ---
>  arch/x86/mm/pat/set_memory.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 

Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>

> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index e9b448d1b1b70..fdc00516c0b54 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -435,8 +435,7 @@ static void cpa_flush(struct cpa_data *data, int cache)
>  static bool overlaps(unsigned long r1_start, unsigned long r1_end,
>  		     unsigned long r2_start, unsigned long r2_end)
>  {
> -	return (r1_start <= r2_end && r1_end >= r2_start) ||
> -		(r2_start <= r1_end && r2_end >= r1_start);
> +	return (r1_start <= r2_end && r1_end >= r2_start);
>  }
>  
>  #ifdef CONFIG_PCI_BIOS