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Date:   Mon, 22 May 2023 17:10:04 -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 3/5] iommu/amd: Introduce Disable IRTE Caching Support
Message-ID: <qbcm4ac4foyafz7xqkkv45exevquu6psqnczwq5dnyrwm3on2o@auwkdo5al2fv>
References: <20230519005529.28171-1-suravee.suthikulpanit@amd.com>
 <20230519005529.28171-4-suravee.suthikulpanit@amd.com>
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On Thu, May 18, 2023 at 08:55:27PM -0400, Suravee Suthikulpanit wrote:
> An Interrupt Remapping Table (IRT) stores interrupt remapping configuration
> for each device. In a normal operation, the AMD IOMMU caches the table
> to optimize subsequent data accesses. This requires the IOMMU driver to
> invalidate IRT whenever it updates the table. The invalidation process
> includes issuing an INVALIDATE_INTERRUPT_TABLE command following by
> a COMPLETION_WAIT command.
> 
> However, there are cases in which the IRT is updated at a high rate.
> For example, for IOMMU AVIC, the IRTE[IsRun] bit is updated on every
> vcpu scheduling (i.e. amd_iommu_update_ga()). On system with large
> amount of vcpus and VFIO PCI pass-through devices, the invalidation
> process could potentially become a performance bottleneck.
> 
> Introducing a new kernel boot option:
> 
>     amd_iommu=irtcachedis
> 
> which disables IRTE caching by setting the IRTCachedis bit in each IOMMU
> Control register, and bypass the IRT invalidation process.
> 
> Co-developed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
> [Awaiting sign-off by Alejandro]
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>

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

> ---
>  .../admin-guide/kernel-parameters.txt         |  1 +
>  drivers/iommu/amd/amd_iommu_types.h           |  4 +++
>  drivers/iommu/amd/init.c                      | 36 +++++++++++++++++++
>  3 files changed, 41 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6221a1d057dd..f29dee600faf 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -323,6 +323,7 @@
>  				       option with care.
>  			pgtbl_v1     - Use v1 page table for DMA-API (Default).
>  			pgtbl_v2     - Use v2 page table for DMA-API.
> +			irtcachedis  - Disable Interrupt Remapping Table (IRT) caching.
>  
>  	amd_iommu_dump=	[HW,X86-64]
>  			Enable AMD IOMMU driver option to dump the ACPI table
> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
> index a0ff1e852efc..486a052e37ca 100644
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -172,6 +172,7 @@
>  #define CONTROL_GAINT_EN	29
>  #define CONTROL_XT_EN		50
>  #define CONTROL_INTCAPXT_EN	51
> +#define CONTROL_IRTCACHEDIS	59
>  #define CONTROL_SNPAVIC_EN	61
>  
>  #define CTRL_INV_TO_MASK	(7 << CONTROL_INV_TIMEOUT)
> @@ -708,6 +709,9 @@ struct amd_iommu {
>  	/* if one, we need to send a completion wait command */
>  	bool need_sync;
>  
> +	/* true if disable irte caching */
> +	bool irtcachedis_enabled;
> +
>  	/* Handle for IOMMU core code */
>  	struct iommu_device iommu;
>  
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index fd487c33b28a..fc0392d706db 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -160,6 +160,7 @@ static int amd_iommu_xt_mode = IRQ_REMAP_XAPIC_MODE;
>  static bool amd_iommu_detected;
>  static bool amd_iommu_disabled __initdata;
>  static bool amd_iommu_force_enable __initdata;
> +static bool amd_iommu_irtcachedis;
>  static int amd_iommu_target_ivhd_type;
>  
>  /* Global EFR and EFR2 registers */
> @@ -477,6 +478,9 @@ static void iommu_disable(struct amd_iommu *iommu)
>  
>  	/* Disable IOMMU hardware itself */
>  	iommu_feature_disable(iommu, CONTROL_IOMMU_EN);
> +
> +	/* Clear IRTE cache disabling bit */
> +	iommu_feature_disable(iommu, CONTROL_IRTCACHEDIS);
>  }
>  
>  /*
> @@ -2700,6 +2704,33 @@ static void iommu_enable_ga(struct amd_iommu *iommu)
>  #endif
>  }
>  
> +static void iommu_disable_irtcachedis(struct amd_iommu *iommu)
> +{
> +	iommu_feature_disable(iommu, CONTROL_IRTCACHEDIS);
> +}
> +
> +static void iommu_enable_irtcachedis(struct amd_iommu *iommu)
> +{
> +	u64 ctrl;
> +
> +	if (!amd_iommu_irtcachedis)
> +		return;
> +
> +	/*
> +	 * Note:
> +	 * The support for IRTCacheDis feature is dertermined by
> +	 * checking if the bit is writable.
> +	 */
> +	iommu_feature_enable(iommu, CONTROL_IRTCACHEDIS);
> +	ctrl = readq(iommu->mmio_base +  MMIO_CONTROL_OFFSET);
> +	ctrl &= (1ULL << CONTROL_IRTCACHEDIS);
> +	if (ctrl)
> +		iommu->irtcachedis_enabled = true;
> +	pr_info("iommu%d (%#06x) : IRT cache is %s\n",
> +		iommu->index, iommu->devid,
> +		iommu->irtcachedis_enabled ? "disabled" : "enabled");
> +}
> +
>  static void early_enable_iommu(struct amd_iommu *iommu)
>  {
>  	iommu_disable(iommu);
> @@ -2710,6 +2741,7 @@ static void early_enable_iommu(struct amd_iommu *iommu)
>  	iommu_set_exclusion_range(iommu);
>  	iommu_enable_ga(iommu);
>  	iommu_enable_xt(iommu);
> +	iommu_enable_irtcachedis(iommu);
>  	iommu_enable(iommu);
>  	iommu_flush_all_caches(iommu);
>  }
> @@ -2760,10 +2792,12 @@ static void early_enable_iommus(void)
>  		for_each_iommu(iommu) {
>  			iommu_disable_command_buffer(iommu);
>  			iommu_disable_event_buffer(iommu);
> +			iommu_disable_irtcachedis(iommu);
>  			iommu_enable_command_buffer(iommu);
>  			iommu_enable_event_buffer(iommu);
>  			iommu_enable_ga(iommu);
>  			iommu_enable_xt(iommu);
> +			iommu_enable_irtcachedis(iommu);
>  			iommu_set_device_table(iommu);
>  			iommu_flush_all_caches(iommu);
>  		}
> @@ -3411,6 +3445,8 @@ static int __init parse_amd_iommu_options(char *str)
>  			amd_iommu_pgtable = AMD_IOMMU_V1;
>  		} else if (strncmp(str, "pgtbl_v2", 8) == 0) {
>  			amd_iommu_pgtable = AMD_IOMMU_V2;
> +		} else if (strncmp(str, "irtcachedis", 11) == 0) {
> +			amd_iommu_irtcachedis = true;
>  		} else {
>  			pr_notice("Unknown option - '%s'\n", str);
>  		}
> -- 
> 2.31.1
>