linux-kernel - Re: [PATCH v5 03/16] x86/mtrr: get MTRR number and support TOP

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Message-ID: <946157a5-fdb2-a45a-63aa-97e9d602e6f0@hygon.cn>
Date:   Tue, 4 Sep 2018 11:02:41 +0800
From:   Pu Wen <puwen@...on.cn>
To:     Borislav Petkov <bp@...en8.de>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, thomas.lendacky@....com, pbonzini@...hat.com,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH v5 03/16] x86/mtrr: get MTRR number and support TOP_MEM2

On 2018/9/4 3:04, Borislav Petkov wrote:
> It was "Hygon Dhyana" before now "Hygon" only. Can we agree on the
> naming nomenclature and stick with it.

OK, agree on it.

...

>> -	if (!((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) &&
>> -	      (boot_cpu_data.x86 >= 0x0f)))
>> +	if (!((boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
>> +	       boot_cpu_data.x86 >= 0x0f) ||
>> +	       boot_cpu_data.x86_vendor == X86_VENDOR_HYGON))
> 
> Why are you even touching this statement? The function returns early on
> !X86_VENDOR_AMD.

The statement is briefly equal to !(X86_VENDOR_AMD || X86_VENDOR_HYGON).
So the function will not return early on !X86_VENDOR_AMD. :-)

Also the statement can be changed to:
+	if (!(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
+	      boot_cpu_data.x86 >= 0x0f) &&
+	    !(boot_cpu_data.x86_vendor == X86_VENDOR_HYGON))
or:
+	if ((boot_cpu_data.x86_vendor != X86_VENDOR_AMD ||
+	     boot_cpu_data.x86 < 0x0f) &&
+	    (boot_cpu_data.x86_vendor != X86_VENDOR_HYGON))

Which statement is better?

Thanks,
Pu Wen