linux-kernel - Re: [PATCH] x86/mm: Simplify redundant overlap calculation

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Date: Tue, 23 Jan 2024 16:54:22 +0000
From: David Binderman <dcb314@...mail.com>
To: Dave Hansen <dave.hansen@...ux.intel.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86/mm: Simplify redundant overlap calculation


Hello there,

>Remove the second condition.  It is exactly the same as the first.

I don't think the first condition is sufficient. I suspect something like

       return (r2_start <= r1_start && r1_start <= r2_end) ||
               (r2_start <= r1_end && r1_end <= r2_end);

Given the range [r2_start .. r2_end], then if r1_start or r1_end
are in that range, you have overlap.

Unless you know different.

Regards

David Binderman



Fixes: 91ee8f5c1f50 ("x86/mm/cpa: Allow range check for static protections")
Reported-by: David Binderman <dcb314@...mail.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org
---
 arch/x86/mm/pat/set_memory.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

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
--
2.34.1