Re: [PATCH] arm64: errata: Add NXP iMX8QM workaround for A53 cache coherency issue

[Mark Rutland]

On Wed, Jul 29, 2026 at 11:28:52AM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@xxxxxxx>
> 
> According to NXP errata document IMX8_1N94W[1], the i.MX8QuadMax SoC
> suffers from a serious cache coherency issue (ERR050104). The upper
> bits, above bit 35, of the ARADDR and ACADDR buses within the Arm A53
> subsystem have been incorrectly connected. This causes some TLBI and IC
> maintenance operations exchanged between the A53 and A72 core clusters
> to be corrupted.
> 
> The workaround requires:
> 
>   - Downgrading targeted TLBI operations to broadcast-all variants.
>     Instead of patching the low-level __TLBI_1 macro (which interferes
>     with the REPEAT_TLBI workaround and causes excessive over-
>     invalidation), redirect high-level TLB flush functions
>     (flush_tlb_mm, __do_flush_tlb_range, flush_tlb_kernel_range,
>     __flush_tlb_kernel_pgtable) to use VMALLE1IS via static key checks.
> 
>   - Upgrading IC IVAU to IC IALLUIS for both kernel (via ALTERNATIVE in
>     invalidate_icache_by_line) and EL0 userspace (via trap-and-upgrade
>     in user_cache_maint_handler with SCTLR_EL1.UCI=0).
> 
>   - Disabling KVM since correct TLB maintenance cannot be guaranteed
>     for guests without the proper devicetree.
> 
>   - No need to touch SMMU Broadcast TLB Maintenance (BTM) since i.MX8QM
>     does not support broadcast TLB.
> 
> SoC detection uses devicetree compatible string "fsl,imx8qm" since the
> boot CPU MIDR_EL1 (0x410fd034) and AIDR_EL1 (0) are not unique to this
> SoC.
> 
> [1] https://www.nxp.com/docs/en/errata/IMX8_1N94W.pdf

[...]

> +	if (alternative_has_cap_unlikely(ARM64_WORKAROUND_NXP_ERR050104)) {
> +		__tlbi(vmalle1is);
> +	} else {
> +		switch (flags & (TLBF_NOWALKCACHE | TLBF_NOBROADCAST)) {
> +		case TLBF_NONE:
> +			__flush_s1_tlb_range_op(vae1is, start, pages, stride,
> +						asid, tlb_level);
> +			break;
> +		case TLBF_NOWALKCACHE:
> +			__flush_s1_tlb_range_op(vale1is, start, pages, stride,
> +						asid, tlb_level);
> +			break;
> +		case TLBF_NOBROADCAST:
> +			/* Combination unused */
> +			BUG();
> +			break;
> +		case TLBF_NOWALKCACHE | TLBF_NOBROADCAST:
> +			__flush_s1_tlb_range_op(vale1, start, pages, stride,
> +						asid, tlb_level);
> +			break;
> +		}
>  	}

Are you sure the workaround needs to be applied for the TLBF_NOBROADCAST
cases? The NXP document lists non-broadcast TLBI instructions, but I
strongly suspect that's in error, as those shouldn't result in
transactions over the core's external interfaces.

[...]

> @@ -585,6 +585,12 @@ static void user_cache_maint_handler(unsigned long esr, struct pt_regs *regs)
>  		__user_cache_maint("dc civac", address, ret);
>  		break;
>  	case ESR_ELx_SYS64_ISS_CRM_IC_IVAU:	/* IC IVAU */
> +		if (cpus_have_final_cap(ARM64_WORKAROUND_NXP_ERR050104)) {
> +			/* ERR050104: upgrade IC IVAU to IC IALLUIS */
> +			asm volatile("ic ialluis");
> +			ret = 0;
> +			break;
> +		}
>  		__user_cache_maint("ic ivau", address, ret);
>  		break;

This doesn't address my feedback on v1:

  https://lore.kernel.org/all/ZIHisLL9FXlbuMLJ@FVFF77S0Q05N/

... which I see Sashiko has also spotted.

Please make this:

	 case ESR_ELx_SYS64_ISS_CRM_IC_IVAU:     /* IC IVAU */
	 	__user_cache_maint("ic ivau", address, ret)
		if (cpus_have_final_cap(ARM64_WORKAROUND_NXP_ERR050104) && !ret)
			asm volatile("ic ialluis");
		break;

If there's a reason that doesn't work, please explain that reason.

Mark.