linux-kernel - Re: [PATCH 10/18] x86/asm/32: Pull MSR_IA32_SYSENTER_CS update code out of native_load

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Message-ID: <20171027201153.GF12039@nazgul.tnic>
Date:   Fri, 27 Oct 2017 22:11:53 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 10/18] x86/asm/32: Pull MSR_IA32_SYSENTER_CS update code
 out of native_load_sp0()

On Thu, Oct 26, 2017 at 01:26:42AM -0700, Andy Lutomirski wrote:
> This causees the MSR_IA32_SYSENTER_CS write to move out of the

Spellcheck pls.

> paravirt hook.  This shouldn't affect Xen PV: Xen already ignores
> MSR_IA32_SYSENTER_ESP writes.  In any event, Xen doesn't support
> vm86() in a useful way.
> 
> Note to any potential backporters: This patch won't break lguest, as
> lguest didn't have any SYSENTER support at all.

...

> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index 11966251cd42..84d6c9f554d0 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -287,6 +287,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
>  	 * current_thread_info().
>  	 */
>  	load_sp0(tss, next);
> +	refresh_sysenter_cs(next);  /* in case prev or next is vm86 */

Ewww, side comments.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--