linux-kernel - Re: [RFC PATCH v3 2/2] selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`

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Message-ID: <48072ce2-e28d-9267-1f8e-3c76682fb782@zytor.com>
Date:   Tue, 24 Jan 2023 12:59:23 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        x86 Mailing List <x86@...nel.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xin Li <xin3.li@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linux Kselftest Mailing List 
        <linux-kselftest@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v3 2/2] selftests/x86: sysret_rip: Add more syscall
 tests with respect to `%rcx` and `%r11`



On 1/24/23 02:09, Ammar Faizi wrote:
> From: Ammar Faizi <ammarfaizi2@...weeb.org>
> 
> Test that:
> 
>   - "syscall" in a FRED system doesn't clobber %rcx and %r11.
>   - "syscall" in a non-FRED system sets %rcx=%rip and %r11=%rflags.
> 
> Test them out with a trivial system call like __NR_getppid and friends
> which are extremely likely to return with SYSRET on an IDT system.
> 
> Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-786b55054126@zytor.com
> Co-developed-by: H. Peter Anvin (Intel) <hpa@...or.com>
> Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
> Acked-by: H. Peter Anvin (Intel) <hpa@...or.com>
> Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>

Add to the description that the purpose of this is to ensure that 
various system calls are *consistent*, as per the comment immediately 
below your code.

	-hpa