Message-ID: <48072ce2-e28d-9267-1f8e-3c76682fb782@zytor.com>
Date:   Tue, 24 Jan 2023 12:59:23 -0800
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Subject: Re: [RFC PATCH v3 2/2] selftests/x86: sysret_rip: Add more syscall
 tests with respect to `%rcx` and `%r11`
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To:     Ammar Faizi <ammarfaizi2@gnuweeb.org>,
        x86 Mailing List <x86@kernel.org>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Xin Li <xin3.li@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Cooper <Andrew.Cooper3@citrix.com>,
        Brian Gerst <brgerst@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Shuah Khan <shuah@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Linux Kselftest Mailing List 
        <linux-kselftest@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <b6e36a5c-6f5e-eda6-54ad-a0c20eb00402@intel.com>
 <25b96960-a07e-a952-5c23-786b55054126@zytor.com>
 <fb1cab9f-a373-38e6-92e6-456332010653@gnuweeb.org>
 <6cd0db14-c9e2-3598-fd10-4b473d78c373@citrix.com>
 <5ecc383c-621b-57d9-7f6d-d63496fca3b3@zytor.com>
 <20230124022729.596997-1-ammarfaizi2@gnuweeb.org>
 <20230124022729.596997-3-ammarfaizi2@gnuweeb.org>
 <ce25e53f-91d4-d793-42a5-036d6bce0b4c@zytor.com>
 <Y899kHYbz32H1S6a@biznet-home.integral.gnuweeb.org>
 <BC632CA8-D2CB-4781-82E5-9810347293B0@zytor.com>
 <Y8+hGxVpgFVcm15g@biznet-home.integral.gnuweeb.org>
 <20230124100926.637335-1-ammarfaizi2@gnuweeb.org>
 <20230124100926.637335-3-ammarfaizi2@gnuweeb.org>
From:   "H. Peter Anvin" <hpa@zytor.com>
In-Reply-To: <20230124100926.637335-3-ammarfaizi2@gnuweeb.org>
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On 1/24/23 02:09, Ammar Faizi wrote:
> From: Ammar Faizi <ammarfaizi2@gnuweeb.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@zytor.com>
> Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> Acked-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.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