linux-kernel - Re: [PATCH v8 05/29] iommu: Add a timeout parameter for PRQ response

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Date:   Mon, 3 Jun 2019 16:32:14 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, joro@...tes.org,
        jacob.jun.pan@...ux.intel.com, yi.l.liu@...el.com,
        jean-philippe.brucker@....com, will.deacon@....com,
        robin.murphy@....com, kevin.tian@...el.com, ashok.raj@...el.com,
        marc.zyngier@....com, peter.maydell@...aro.org,
        vincent.stehle@....com
Subject: Re: [PATCH v8 05/29] iommu: Add a timeout parameter for PRQ
 response

On Sun, 26 May 2019 18:09:40 +0200
Eric Auger <eric.auger@...hat.com> wrote:

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> 
> When an IO page request is processed outside IOMMU subsystem, response
> can be delayed or lost. Add a tunable setup parameter such that user can
> choose the timeout for IOMMU to track pending page requests.
> 
> This timeout mechanism is a basic safety net which can be implemented in
> conjunction with credit based or device level page response exception
> handling.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |  8 +++++
>  drivers/iommu/iommu.c                         | 29 +++++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 138f6664b2e2..b43f0893d252 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1813,6 +1813,14 @@
>  			1 - Bypass the IOMMU for DMA.
>  			unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
>  
> +	iommu.prq_timeout=
> +			Timeout in seconds to wait for page response
> +			of a pending page request.
> +			Format: <integer>
> +			Default: 10
> +			0 - no timeout tracking
> +			1 to 100 - allowed range
> +
>  	io7=		[HW] IO7 for Marvel based alpha systems
>  			See comment before marvel_specify_io7 in
>  			arch/alpha/kernel/core_marvel.c.
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 13b301cfb10f..64e87d56f471 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -45,6 +45,19 @@ static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>  #endif
>  static bool iommu_dma_strict __read_mostly = true;
>  
> +/*
> + * Timeout to wait for page response of a pending page request. This is
> + * intended as a basic safty net in case a pending page request is not
> + * responded for an exceptionally long time. Device may also implement
> + * its own protection mechanism against this exception.
> + * Units are in jiffies with a range between 1 - 100 seconds equivalent.
> + * Default to 10 seconds.
> + * Setting 0 means no timeout tracking.
> + */
> +#define IOMMU_PAGE_RESPONSE_MAX_TIMEOUT (HZ * 100)
> +#define IOMMU_PAGE_RESPONSE_DEF_TIMEOUT (HZ * 10)
> +static unsigned long prq_timeout = IOMMU_PAGE_RESPONSE_DEF_TIMEOUT;
> +
>  struct iommu_group {
>  	struct kobject kobj;
>  	struct kobject *devices_kobj;
> @@ -157,6 +170,22 @@ static int __init iommu_dma_setup(char *str)
>  }
>  early_param("iommu.strict", iommu_dma_setup);
>  
> +static int __init iommu_set_prq_timeout(char *str)
> +{
> +	unsigned long timeout;
> +
> +	if (!str)
> +		return -EINVAL;
> +	timeout = simple_strtoul(str, NULL, 0);
> +	timeout = timeout * HZ;
> +	if (timeout > IOMMU_PAGE_RESPONSE_MAX_TIMEOUT)
> +		return -EINVAL;
> +	prq_timeout = timeout;
> +
> +	return 0;
> +}
> +early_param("iommu.prq_timeout", iommu_set_prq_timeout);
> +
>  static ssize_t iommu_group_attr_show(struct kobject *kobj,
>  				     struct attribute *__attr, char *buf)
>  {

It doesn't seem to make much sense to include this patch without also
including "iommu: handle page response timeout".  Was that one lost?
Dropped?  Lives elsewhere?  Thanks,

Alex