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

[David Binderman]

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@xxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
---
 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