linux-kernel - Re: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled

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Date:   Wed, 29 Nov 2017 13:47:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling
 with IRQ state tracing enabled

On Wed, Nov 29, 2017 at 08:09:51AM +0100, Ingo Molnar wrote:
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index f81d50d7ceac..c0b52df8ee4f 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -945,16 +945,16 @@ idtentry simd_coprocessor_error		do_simd_coprocessor_error	has_error_code=0
>  	 */
>  ENTRY(native_load_gs_index)
>  	FRAME_BEGIN
> +	SWAPGS					/* switch from user GS to kernel GS */
>  	pushfq
>  	DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
>  	TRACE_IRQS_OFF
> -	SWAPGS

I'm thinking those moves it too far back; we should at least have
interrupts disabled when we do SWAPGS, no? Also, curse paravirt.