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Mon, 17 Nov 2025 19:45:41 +0000 Message-ID: Date: Mon, 17 Nov 2025 11:45:38 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 6/8] x86/traps: Communicate a LASS violation in #GP message Content-Language: en-US To: Borislav Petkov CC: , Dave Hansen , "Thomas Gleixner" , Ingo Molnar , "Jonathan Corbet" , "H . 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That comment still reads weird: > I see. The idea with the comment was to clarify why the check is outside cpu_feature_enabled(X86_FEATURE_LASS). That clearly failed! :) > I guess you want to have > > if (cpu_feature_enabled(X86_FEATURE_LASS)) { > if (*addr < PAGE_SIZE) > return GP_NULL_POINTER; > else > return GP_LASS_VIOLATION; > } > > so that it is perfectly clear. > You are right. The condition would typically hit only with LASS enabled. But since we are adding an extra hint for NULL pointers, I figured it would be helpful even without LASS (even though it is unlikely to happen). Therefore, the printed message isn't LASS specific either: Oops: general protection fault, kernel NULL pointer dereference 0x0: Also, it makes the code a tiny bit prettier (aesthetically, without the nested if). We now have 4 hints and a check for each: if (condition1) return HINT_1; ... if (condition4) return HINT_4; Would this update to the comment help clarify? /* * A NULL pointer dereference usually causes a #PF. However, it * can result in a #GP when LASS is active. Provide the same * hint in the rare case that the condition is hit without LASS. */ if (*addr < PAGE_SIZE) return GP_NULL_POINTER; /* * Assume that LASS caused the exception, because the address is * canonical and in the user half. */ if (cpu_feature_enabled(X86_FEATURE_LASS)) return GP_LASS_VIOLATION; Though, I won't push for it further. Code clarity is more important than reducing indentation.