linux-kernel - Re: [PATCH 6/6] arm64: trap userspace "dc cvau" cache operation on errata-affected core

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Date:	Tue, 14 Jun 2016 17:16:50 +0100
From:	Suzuki K Poulose <Suzuki.Poulose@....com>
To:	Andre Przywara <andre.przywara@....com>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] arm64: trap userspace "dc cvau" cache operation on
 errata-affected core

On 09/05/16 17:49, Andre Przywara wrote:
> The ARM errata 819472, 826319, 827319 and 824069 for affected
> Cortex-A53 cores demand to promote "dc cvau" instructions to
> "dc civac". Since we allow userspace to also emit those instructions,
> we should make sure that "dc cvau" gets promoted there too.
> So lets grasp the nettle here and actually trap every userland cache
> maintenance instruction once we detect at least one affected core in
> the system.
> We then emulate the instruction by executing it on behalf of userland,
> promoting "dc cvau" to "dc civac" on the way and injecting access
> fault back into userspace.
>
> Signed-off-by: Andre Przywara <andre.przywara@....com>


> +
> +asmlinkage void __exception do_sysinstr(unsigned int esr, struct pt_regs *regs)
> +{
> +	unsigned long address;
> +	int ret;
> +
> +	/* if this is a write with: Op0=1, Op2=1, Op1=3, CRn=7 */
> +	if ((esr & 0x01fffc01) == 0x0012dc00) {
> +		int rt = (esr >> 5) & 0x1f;
> +		int crm = (esr >> 1) & 0x0f;
> +
> +		address = regs->regs[rt];
> +
> +		switch (crm) {
> +		case 11:		/* DC CVAU, gets promoted */
> +			__user_cache_maint("dc civac", address, ret);
> +			break;
> +		case 10:		/* DC CVAC, gets promoted */
> +			__user_cache_maint("dc civac", address, ret);
> +			break;
> +		case 14:		/* DC CIVAC */
> +			__user_cache_maint("dc civac", address, ret);
> +			break;
> +		case 5:			/* IC IVAU */
> +			__user_cache_maint("ic ivau", address, ret);
> +			break;
> +		default:
> +			force_signal_inject(SIGILL, ILL_ILLOPC, regs, 0);
> +			return;
> +		}
> +	} else {
> +		force_signal_inject(SIGILL, ILL_ILLOPC, regs, 0);
> +		return;

Correct me if I am wrong, I think we should handle DC ZVA and emulate the same ?
Thats the only EL0 accessible instruction we don't handle above.

Suzuki