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From: John Garry <>
To: Robin Murphy <>, <>,
Subject: Re: [PATCH] iommu: Print default strict or lazy mode at init time
Date: Tue, 1 Jun 2021 18:44:00 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

>> pr_info("DMA domain default TLB invalidation policy: %s mode %s\n",
>>                iommu_dma_strict ? "strict" : "lazy",
>>                 (iommu_cmd_line & IOMMU_CMD_LINE_STRICT) ?
>>                         "(set via kernel command line)" : "");
>> I think it's worth mentioning "default" somewhere, as not all IOMMUs 
>> or devices will use lazy mode even if it's default.
> But that's part of what I think is misleading - I boot and see that the 
> default is something, so I reboot with iommu.strict to explicitly set it 
> the other way, but now that's the default... huh?
> The way I see it, we're saying what the current IOMMU API policy is - 
> the value of iommu_dma_strict at any given time is fact - but we're not 
> necessarily saying how widely that policy is enforced. We similarly 
> report the type for default domains from global policy even though that 
> may also be overridden per-group by drivers and/or userspace later; 

> we 
> don't say it's the *default* default domain type.

I think that is this is the behavior a user would understand from that 

However from a glance at the intel IOMMU driver, it seems possible to 
change default domain type after iommu_subsys_init().

> However, having now debugged the AMD issue from another thread, I think 
> doing this at subsys_initcall is in fact going to be too early to be 
> meaningful, since it ignores drivers' ability to change the global 
> policy :(

A user may still learn the IOMMU group domain type from sysfs. There is 
no such thing for TLB invalidation mode - how about add a file for this? 
It would be useful.

iommu mailing list

      reply	other threads:[~2021-06-01 17:45 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-28 13:37 [PATCH] iommu: Print default strict or lazy mode at init time John Garry
2021-06-01  9:09 ` Robin Murphy
2021-06-01 15:50   ` John Garry
2021-06-01 16:42     ` Robin Murphy
2021-06-01 17:44       ` John Garry [this message]

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