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Date: Mon, 15 Aug 2016 11:52:06 +0100
From: Catalin Marinas <>
To: Ard Biesheuvel <>
Cc: Will Deacon <>, Mark Rutland <>,
	Kees Cook <>,,
	Julien Grall <>,
	James Morse <>,
	"" <>
Subject: Re: [PATCH 0/7] arm64: Privileged Access Never
 using TTBR0_EL1 switching

On Mon, Aug 15, 2016 at 12:43:31PM +0200, Ard Biesheuvel wrote:
> But, how about we store the reserved ASID in TTBR1_EL1 instead, and
> switch TCR_EL1.A1 and TCR_EL1.EPD0 in a single write? That way, we can
> switch ASIDs and disable table walks atomically (I hope), and we
> wouldn't need to change TTBR0_EL1 at all.

I did this before for AArch32 + LPAE (patches on the list sometime last
year I think). But the idea was nak'ed by the ARM architects. The
TCR_EL1.A1 can be cached somewhere in the TLB state machine, so you need
TLBI (IOW, toggling A1 does not guarantee an ASID switch).


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