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Date: Tue, 28 Nov 2017 17:48:00 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Ingo Molnar <mingo@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 15/24] x86/mm: Allow flushing for future ASID switches
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On Tue, Nov 28, 2017 at 05:39:08PM +0100, Peter Zijlstra wrote:

> @@ -220,7 +221,21 @@ For 32-bit we have the following conventions - kernel is built with
>  .macro SWITCH_TO_USER_CR3 scratch_reg:req
>  	STATIC_JUMP_IF_FALSE .Lend_\@, kaiser_enabled_key, def=1
>  	mov	%cr3, \scratch_reg
> -	ADJUST_USER_CR3 \scratch_reg
> +	push	\scratch_reg
> +	andq	$(0x7FF), \scratch_reg
> +	bt	\scratch_reg, PER_CPU_VAR(__asid_flush)
> +	jnc	.Lnoflush_\@
> +
> +	btr	\scratch_reg, PER_CPU_VAR(__asid_flush)
> +	pop	\scratch_reg
> +	jmp	.Ldo_\@
> +
> +.Lnoflush_\@:
> +	pop	\scratch_reg
> +	ALTERNATIVE "", "bts $63, \scratch_reg", X86_FEATURE_PCID
> +
> +.Ldo_\@:
> +	orq     $(KAISER_SWITCH_MASK), \scratch_reg
>  	mov	\scratch_reg, %cr3
>  .Lend_\@:
>  .endm

Ah, I suppose I should also deal with RESTORE_CR3...