linux-kernel - Re: the x86 sysret_rip test fails on the Intel FRED architecture

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Message-ID: <65D9F1DE-96D4-4CC7-A21C-A740B7DDE0C8@zytor.com>
Date:   Sat, 21 Jan 2023 20:44:38 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        "Li, Xin3" <xin3.li@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: the x86 sysret_rip test fails on the Intel FRED architecture

On January 21, 2023 8:34:09 PM PST, Dave Hansen <dave.hansen@...el.com> wrote:
>On 1/21/23 19:38, Li, Xin3 wrote:
>>> However, it doesn't seem to make sense to do so to me. The current behavior is
>>> much more of an artifact than desired behavior.
>> We kind of have an agreement that %r11 = %flags after returning from the kernel.
>> 
>> And the question is, is it what we want?
>
>Can the selftest just set r11=rflags before the syscall?  The old
>syscall entry path will set r11=rflags.  The FRED path won't touch it.
>Either case will pass an r11==rflags check.

That's a good idea.