From: John Garry <john.garry@huawei.com>
To: Robin Murphy <robin.murphy@arm.com>, <joro@8bytes.org>,
<will@kernel.org>
Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
hch@lst.de
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: <72eb3de9-1d1c-ae46-c5a9-95f26525d435@huawei.com> (raw)
In-Reply-To: <58ea001c-4c37-9c5a-77be-38ac3bea2476@arm.com>
>>
>> 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
message.
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.
Thanks,
John
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prev parent 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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