linux-kernel - Re: [PATCH v2] x86/xen/64: Rearrange the SYSCALL entries

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Date:   Wed, 9 Aug 2017 17:39:12 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>
Cc:     Borislav Petkov <bpetkov@...e.de>, linux-kernel@...r.kernel.org,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2] x86/xen/64: Rearrange the SYSCALL entries

On 08/08/17 05:59, Andy Lutomirski wrote:
> Xen's raw SYSCALL entries are much less weird than native.  Rather
> than fudging them to look like native entries, use the Xen-provided
> stack frame directly.
> 
> This lets us eliminate entry_SYSCALL_64_after_swapgs and two uses of
> the SWAPGS_UNSAFE_STACK paravirt hook.  The SYSENTER code would
> benefit from similar treatment.
> 
> This makes one change to the native code path: the compat
> instruction that clears the high 32 bits of %rax is moved slightly
> later.  I'd be surprised if this affects performance at all.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>

Reviewed-by: Juergen Gross <jgross@...e.com>
Tested-by: Juergen Gross <jgross@...e.com>


Thanks,

Juergen