Re: [PATCH v1 5/7] iommu/arm-smmu-v3: Skip cd sync if CD table isn't active

From: Jason Gunthorpe <jgg@nvidia.com>
To: Michael Shavit <mshavit@google.com>
Cc: Will Deacon <will@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Joerg Roedel <joro@8bytes.org>,
	jean-philippe@linaro.org, nicolinc@nvidia.com,
	baolu.lu@linux.intel.com, linux-arm-kernel@lists.infradead.org,
	iommu@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 5/7] iommu/arm-smmu-v3: Skip cd sync if CD table isn't active
Date: Thu, 27 Jul 2023 15:33:40 -0300	[thread overview]
Message-ID: <ZMK4hEJXb2m36VOF@nvidia.com> (raw)
In-Reply-To: <20230727182647.4106140-6-mshavit@google.com>

On Fri, Jul 28, 2023 at 02:26:21AM +0800, Michael Shavit wrote:
> This commit explicitly keeps track of whether a CD table is installed in
> an STE so that arm_smmu_sync_cd can skip the sync when unnecessary. This
> was previously achieved through the domain->devices list, but we are
> moving to a model where arm_smmu_sync_cd directly operates on a master
> and the master's CD table instead of a domain.
> 
> Signed-off-by: Michael Shavit <mshavit@google.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 4 ++++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 2 ++
>  2 files changed, 6 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 654acf6002bf3..af7949b62327b 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -987,6 +987,9 @@ static void arm_smmu_sync_cd(struct arm_smmu_domain *smmu_domain,
>  		},
>  	};
>  
> +	if (!smmu_domain->cd_table.installed)
> +		return;
> +
>  	cmds.num = 0;
>  
>  	spin_lock_irqsave(&smmu_domain->devices_lock, flags);
> @@ -1368,6 +1371,7 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
>  				  cd_table->l1_desc ?
>  					  STRTAB_STE_0_S1FMT_64K_L2 :
>  					  STRTAB_STE_0_S1FMT_LINEAR);
> +		cd_table->installed = true;
>  	}
>  
>  	if (s2_cfg) {
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> index 0e55ca0d40e6b..f301efe90b599 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> @@ -599,6 +599,8 @@ struct arm_smmu_ctx_desc_cfg {
>  	u8				max_cds_bits;
>  	/* Whether CD entries in this table have the stall bit set. */
>  	bool				stall_enabled;
> +	/* Whether this CD table is installed in any STE */
> +	bool                            installed;

Do

u8 xx:1;
u8 yy:1;

For these things, Linus has complained about lists of bools in structs
before.

Jason