linux-kernel - Re: [PATCH v2 23/24] iommu/arm-smmu: Allow non-strict in pgtable

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Message-ID: <20210802130438.GA28547@willie-the-truck>
Date:   Mon, 2 Aug 2021 14:04:39 +0100
From:   Will Deacon <will@...nel.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     joro@...tes.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        suravee.suthikulpanit@....com, baolu.lu@...ux.intel.com,
        john.garry@...wei.com, dianders@...omium.org
Subject: Re: [PATCH v2 23/24] iommu/arm-smmu: Allow non-strict in
 pgtable_quirks interface

On Wed, Jul 28, 2021 at 04:58:44PM +0100, Robin Murphy wrote:
> To make io-pgtable aware of a flush queue being dynamically enabled,
> allow IO_PGTABLE_QUIRK_NON_STRICT to be set even after a domain has been
> attached to, and hook up the final piece of the puzzle in iommu-dma.
> 
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 15 +++++++++++++++
>  drivers/iommu/arm/arm-smmu/arm-smmu.c       | 11 +++++++++++
>  drivers/iommu/dma-iommu.c                   |  3 +++
>  3 files changed, 29 insertions(+)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 19400826eba7..40fa9cb382c3 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2711,6 +2711,20 @@ static int arm_smmu_enable_nesting(struct iommu_domain *domain)
>  	return ret;
>  }
>  
> +static int arm_smmu_set_pgtable_quirks(struct iommu_domain *domain,
> +		unsigned long quirks)
> +{
> +	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
> +
> +	if (quirks == IO_PGTABLE_QUIRK_NON_STRICT && smmu_domain->pgtbl_ops) {
> +		struct io_pgtable *iop = io_pgtable_ops_to_pgtable(smmu_domain->pgtbl_ops);
> +
> +		iop->cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
> +		return 0;
> +	}
> +	return -EINVAL;
> +}

I don't see anything serialising this against a concurrent iommu_unmap(), so
the ordering and atomicity looks quite suspicious to me here. I don't think
it's just the page-table quirks either, but also setting cookie->fq_domain.

Will