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Date:   Mon, 22 May 2023 17:22:16 -0700
From:   Jerry Snitselaar <jsnitsel@redhat.com>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Cc:     linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
        joro@8bytes.org, joao.m.martins@oracle.com,
        alejandro.j.jimenez@oracle.com, boris.ostrovsky@oracle.com,
        jon.grimm@amd.com, santosh.shukla@amd.com, vasant.hegde@amd.com,
        kishon.vijayabraham@amd.com
Subject: Re: [PATCH v2 5/5] iommu/amd: Improving Interrupt Remapping Table
 Invalidation
Message-ID: <sxyc5b2ifguf7r3krewwp4o42uzqlkhvshhc4m2nhkumedgy5s@r2arntwzmmpa>
References: <20230519005529.28171-1-suravee.suthikulpanit@amd.com>
 <20230519005529.28171-6-suravee.suthikulpanit@amd.com>
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In-Reply-To: <20230519005529.28171-6-suravee.suthikulpanit@amd.com>
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On Thu, May 18, 2023 at 08:55:29PM -0400, Suravee Suthikulpanit wrote:
> Invalidating Interrupt Remapping Table (IRT) requires, the AMD IOMMU driver
> to issue INVALIDATE_INTERRUPT_TABLE and COMPLETION_WAIT commands.
> Currently, the driver issues the two commands separately, which requires
> calling raw_spin_lock_irqsave() twice. In addition, the COMPLETION_WAIT
> could potentially be interleaved with other commands causing delay of
> the COMPLETION_WAIT command.
> 
> Therefore, combine issuing of the two commands in one spin-lock, and
> changing struct amd_iommu.cmd_sem_val to use atomic64 to minimize
> locking.
> 
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>

> ---
>  drivers/iommu/amd/amd_iommu_types.h |  2 +-
>  drivers/iommu/amd/init.c            |  2 +-
>  drivers/iommu/amd/iommu.c           | 27 ++++++++++++++++++++++-----
>  3 files changed, 24 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
> index 486a052e37ca..2fa65da2a9a5 100644
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -744,7 +744,7 @@ struct amd_iommu {
>  
>  	u32 flags;
>  	volatile u64 *cmd_sem;
> -	u64 cmd_sem_val;
> +	atomic64_t cmd_sem_val;
>  
>  #ifdef CONFIG_AMD_IOMMU_DEBUGFS
>  	/* DebugFS Info */
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index fc0392d706db..16737819f79a 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -1750,7 +1750,7 @@ static int __init init_iommu_one(struct amd_iommu *iommu, struct ivhd_header *h,
>  	iommu->pci_seg = pci_seg;
>  
>  	raw_spin_lock_init(&iommu->lock);
> -	iommu->cmd_sem_val = 0;
> +	atomic64_set(&iommu->cmd_sem_val, 0);
>  
>  	/* Add IOMMU to internal data structures */
>  	list_add_tail(&iommu->list, &amd_iommu_list);
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index 51c2b018433d..57ae4a8072d3 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -1182,11 +1182,11 @@ static int iommu_completion_wait(struct amd_iommu *iommu)
>  	if (!iommu->need_sync)
>  		return 0;
>  
> -	raw_spin_lock_irqsave(&iommu->lock, flags);
> -
> -	data = ++iommu->cmd_sem_val;
> +	data = atomic64_add_return(1, &iommu->cmd_sem_val);
>  	build_completion_wait(&cmd, iommu, data);
>  
> +	raw_spin_lock_irqsave(&iommu->lock, flags);
> +
>  	ret = __iommu_queue_command_sync(iommu, &cmd, false);
>  	if (ret)
>  		goto out_unlock;
> @@ -1284,11 +1284,28 @@ static void amd_iommu_flush_irt_all(struct amd_iommu *iommu)
>  
>  static void iommu_flush_irt_and_complete(struct amd_iommu *iommu, u16 devid)
>  {
> +	int ret;
> +	u64 data;
> +	unsigned long flags;
> +	struct iommu_cmd cmd, cmd2;
> +
>  	if (iommu->irtcachedis_enabled)
>  		return;
>  
> -	iommu_flush_irt(iommu, devid);
> -	iommu_completion_wait(iommu);
> +	build_inv_irt(&cmd, devid);
> +	data = atomic64_add_return(1, &iommu->cmd_sem_val);
> +	build_completion_wait(&cmd2, iommu, data);
> +
> +	raw_spin_lock_irqsave(&iommu->lock, flags);
> +	ret = __iommu_queue_command_sync(iommu, &cmd, true);
> +	if (ret)
> +		goto out;
> +	ret = __iommu_queue_command_sync(iommu, &cmd2, false);
> +	if (ret)
> +		goto out;
> +	wait_on_sem(iommu, data);
> +out:
> +	raw_spin_unlock_irqrestore(&iommu->lock, flags);
>  }
>  
>  void iommu_flush_all_caches(struct amd_iommu *iommu)
> -- 
> 2.31.1
>