linux-kernel - Re: [PATCH v2 1/1] x86/ia32: Normalize any null selector value to 0

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Message-ID: <3ff385ea-0b7a-441f-9905-4aad54c7575d@zytor.com>
Date: Wed, 20 Nov 2024 19:54:54 -0800
From: Xin Li <xin@...or.com>
To: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: bp@...en8.de, brgerst@...il.com, dave.hansen@...ux.intel.com,
        ebiederm@...ssion.com, hpa@...or.com, linux-kernel@...r.kernel.org,
        mingo@...hat.com, tglx@...utronix.de, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2 1/1] x86/ia32: Normalize any null selector value to 0

On 11/20/2024 11:34 AM, Andrew Cooper wrote:
> On 20/11/2024 7:09 pm, Xin Li wrote:
>> On 11/20/2024 1:33 AM, Andrew Cooper wrote:
>>> Right now, this change is codifying the problem behaviour we were trying
>>> to fix out under FRED.
>>>
>>> Under FRED, if userspace loads e.g. 2 into a selector, it should remain
>>> 2 until userspace changes it to something else.
>>
>> Okay, I will fix it by:
>> 1) For null selector values, do nothing.
>> 2) For non-null selector values, set RPL bits.
>>
>> sounds okay?
> 
> Yeah, that sounds okay.

Actually this is what v1 does:

https://lore.kernel.org/lkml/20230706052231.2183-1-xin3.li@intel.com/

But obviously I need to rewrite the change log.

> 
> The selftest ought to work under FRED, but it was speculative coding.  I
> can't rule out that tweaks might be needed.

The v1 makes the test happy with both IDT and FRED.

Thanks!
     Xin