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Subject: Re: [Xen-devel] [PATCH v2] xen: get rid of paravirt op
 adjust_exception_frame
To: Andy Lutomirski <luto@amacapital.net>, Juergen Gross <jgross@suse.com>
Cc: X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Thomas Gleixner <tglx@linutronix.de>
References: <20170801103954.23904-1-jgross@suse.com>
 <CALCETrXzn64KH=xOxMSpa+-DjHx_p87gX50noaqQaSFMMZFfQQ@mail.gmail.com>
From: Andrew Cooper <andrew.cooper3@citrix.com>
Message-ID: <5c14a9a9-7b13-50d0-2338-2bccac7b7ac3@citrix.com>
Date: Wed, 2 Aug 2017 00:38:59 +0100
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On 01/08/2017 20:45, Andy Lutomirski wrote:
> Also, IMO it would be nice to fully finish the job.  Remaining steps are:
>
> 1. Unsuck the SYSCALL entries on Xen PV.
> 2. Unsuck the SYENTER entry on Xen PV.
> 3. Make a xen_nmi that's actually correct (should be trivial)
>
> #1 is here:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_syscall&id=14fee348e3e86c994400d68085217d1232a637d6

If the

/* Zero-extending 32-bit regs, do not remove */
movl    %eax, %eax

comments are to be believed, then the entry logic needs reordering
slightly to:

GLOBAL(entry_*_compat_after_hwframe)
    movl    %eax, %eax    /* Zero-extending 32-bit regs, do not remove */
    pushq    %rax                /* pt_regs->orig_ax */

~Andrew

(It is unfortunate this can't be simplified to pushq %eax)