linux-kernel - RE: [RFC PATCH v3 0/2] selftests/x86: sysret

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Message-ID: <SA1PR11MB6734D1FC972F663487E9140DA8C99@SA1PR11MB6734.namprd11.prod.outlook.com>
Date:   Tue, 24 Jan 2023 23:20:11 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     "H. Peter Anvin" <hpa@...or.com>,
        Ammar Faizi <ammarfaizi2@...weeb.org>,
        x86 Mailing List <x86@...nel.org>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "andrew.cooper3@...rix.com" <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>,
        "Lutomirski, Andy" <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 0/2] selftests/x86: sysret_rip update for FRED
 system

> >>
> >> Xin Li reported sysret_rip test fails at:
> >>
> >>         assert(ctx->uc_mcontext.gregs[REG_EFL] ==
> >>                ctx->uc_mcontext.gregs[REG_R11]);
> >
> >On FRED systems, flags is 0x200a93 and r11 is 0xfeedfacedeadbeef here.
> >
> >We need to remove or change this assertion, maybe:
> >  assert(ctx->uc_mcontext.gregs[REG_EFL] == ctx->uc_mcontext.gregs[REG_R11] ||
> >         r11_sentinel == ctx->uc_mcontext.gregs[REG_R11]);
> >
> >>
> >> in a FRED system. Let's handle the FRED system scenario too. The 'syscall'
> >> instruction in a FRED system doesn't set %r11=%rflags.
> >>
> 
> This should use check_regs_result() – which is exactly the reason I made that a
> separate function.

Exactly.