linux-kernel - Re: [PATCH v13 05/15] iommu/smmuv3: Get prepared for nested stage support

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Date:   Tue, 2 Feb 2021 15:14:56 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     Eric Auger <eric.auger@...hat.com>, <eric.auger.pro@...il.com>,
        <iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
        <kvm@...r.kernel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <will@...nel.org>, <joro@...tes.org>, <maz@...nel.org>,
        <robin.murphy@....com>, <alex.williamson@...hat.com>
CC:     <jean-philippe@...aro.org>, <jacob.jun.pan@...ux.intel.com>,
        <nicoleotsuka@...il.com>, <vivek.gautam@....com>,
        <yi.l.liu@...el.com>, <zhangfei.gao@...aro.org>
Subject: Re: [PATCH v13 05/15] iommu/smmuv3: Get prepared for nested stage
 support

Hi Eric,

On 2020/11/18 19:21, Eric Auger wrote:
> When nested stage translation is setup, both s1_cfg and
> s2_cfg are set.
> 
> We introduce a new smmu domain abort field that will be set
> upon guest stage1 configuration passing.
> 
> arm_smmu_write_strtab_ent() is modified to write both stage
> fields in the STE and deal with the abort field.
> 
> In nested mode, only stage 2 is "finalized" as the host does
> not own/configure the stage 1 context descriptor; guest does.
> 
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> 
> ---
> v10 -> v11:
> - Fix an issue reported by Shameer when switching from with vSMMU
>   to without vSMMU. Despite the spec does not seem to mention it
>   seems to be needed to reset the 2 high 64b when switching from
>   S1+S2 cfg to S1 only. Especially dst[3] needs to be reset (S2TTB).
>   On some implementations, if the S2TTB is not reset, this causes
>   a C_BAD_STE error
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 64 +++++++++++++++++----
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  2 +
>  2 files changed, 56 insertions(+), 10 deletions(-)
> 
> 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 18ac5af1b284..412ea1bafa50 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -1181,8 +1181,10 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>  	 * three cases at the moment:
>  	 *
>  	 * 1. Invalid (all zero) -> bypass/fault (init)
> -	 * 2. Bypass/fault -> translation/bypass (attach)
> -	 * 3. Translation/bypass -> bypass/fault (detach)
> +	 * 2. Bypass/fault -> single stage translation/bypass (attach)
> +	 * 3. Single or nested stage Translation/bypass -> bypass/fault (detach)
> +	 * 4. S2 -> S1 + S2 (attach_pasid_table)
> +	 * 5. S1 + S2 -> S2 (detach_pasid_table)

The following line "BUG_ON(ste_live && !nested);" forbids this transform.
And I have a look at the 6th patch, the transform seems S1 + S2 -> abort.
So after detach, the status is not the same as that before attach. Does it
match our expectation?

>  	 *
>  	 * Given that we can't update the STE atomically and the SMMU
>  	 * doesn't read the thing in a defined order, that leaves us
> @@ -1193,7 +1195,8 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>  	 * 3. Update Config, sync
>  	 */
>  	u64 val = le64_to_cpu(dst[0]);
> -	bool ste_live = false;
> +	bool s1_live = false, s2_live = false, ste_live;
> +	bool abort, nested = false, translate = false;
>  	struct arm_smmu_device *smmu = NULL;
>  	struct arm_smmu_s1_cfg *s1_cfg;
>  	struct arm_smmu_s2_cfg *s2_cfg;
> @@ -1233,6 +1236,8 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>  		default:
>  			break;
>  		}
> +		nested = s1_cfg->set && s2_cfg->set;
> +		translate = s1_cfg->set || s2_cfg->set;
>  	}
>  
>  	if (val & STRTAB_STE_0_V) {
> @@ -1240,23 +1245,36 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>  		case STRTAB_STE_0_CFG_BYPASS:
>  			break;
>  		case STRTAB_STE_0_CFG_S1_TRANS:
> +			s1_live = true;
> +			break;
>  		case STRTAB_STE_0_CFG_S2_TRANS:
> -			ste_live = true;
> +			s2_live = true;
> +			break;
> +		case STRTAB_STE_0_CFG_NESTED:
> +			s1_live = true;
> +			s2_live = true;
>  			break;
>  		case STRTAB_STE_0_CFG_ABORT:
> -			BUG_ON(!disable_bypass);
>  			break;
>  		default:
>  			BUG(); /* STE corruption */
>  		}
>  	}
>  
> +	ste_live = s1_live || s2_live;
> +
>  	/* Nuke the existing STE_0 value, as we're going to rewrite it */
>  	val = STRTAB_STE_0_V;
>  
>  	/* Bypass/fault */
> -	if (!smmu_domain || !(s1_cfg->set || s2_cfg->set)) {
> -		if (!smmu_domain && disable_bypass)
> +
> +	if (!smmu_domain)
> +		abort = disable_bypass;
> +	else
> +		abort = smmu_domain->abort;
> +
> +	if (abort || !translate) {
> +		if (abort)
>  			val |= FIELD_PREP(STRTAB_STE_0_CFG, STRTAB_STE_0_CFG_ABORT);
>  		else
>  			val |= FIELD_PREP(STRTAB_STE_0_CFG, STRTAB_STE_0_CFG_BYPASS);
> @@ -1274,8 +1292,16 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>  		return;
>  	}
>  
> +	BUG_ON(ste_live && !nested);
> +
> +	if (ste_live) {
> +		/* First invalidate the live STE */
> +		dst[0] = cpu_to_le64(STRTAB_STE_0_CFG_ABORT);
> +		arm_smmu_sync_ste_for_sid(smmu, sid);
> +	}
> +
[...]

Thanks,
Keqian