From: John Garry <john.garry@huawei.com>
To: Lu Baolu <baolu.lu@linux.intel.com>, <joro@8bytes.org>,
<will@kernel.org>, <dwmw2@infradead.org>, <robin.murphy@arm.com>,
<corbet@lwn.net>
Cc: <linux-kernel@vger.kernel.org>,
<iommu@lists.linux-foundation.org>, <linuxarm@huawei.com>,
<thunder.leizhen@huawei.com>, <chenxiang66@hisilicon.com>,
<linux-doc@vger.kernel.org>
Subject: Re: [PATCH v13 4/6] iommu/vt-d: Add support for IOMMU default DMA mode build options
Date: Thu, 17 Jun 2021 09:00:37 +0100 [thread overview]
Message-ID: <f3fe6c4b-f360-ab7b-7ad2-ced63269499d@huawei.com> (raw)
In-Reply-To: <46dbce5c-1c2b-60d4-df56-d2b95a959425@linux.intel.com>
On 17/06/2021 08:32, Lu Baolu wrote:
> On 6/16/21 7:03 PM, John Garry wrote:
>> @@ -4382,9 +4380,9 @@ int __init intel_iommu_init(void)
>> * is likely to be much lower than the overhead of
>> synchronizing
>> * the virtual and physical IOMMU page-tables.
>> */
>> - if (!intel_iommu_strict && cap_caching_mode(iommu->cap)) {
>> - pr_warn("IOMMU batching is disabled due to virtualization");
>> - intel_iommu_strict = 1;
>> + if (cap_caching_mode(iommu->cap)) {
>> + pr_warn("IOMMU batching disallowed due to
>> virtualization\n");
>> + iommu_set_dma_strict(true);
>
> With this change, VM guest will always show this warning.
Would they have got it before also normally?
I mean, default is intel_iommu_strict=0, so if
cap_caching_mode(iommu->cap) is true and intel_iommu_strict not set to 1
elsewhere previously, then we would get this print.
> How about
> removing this message? Users could get the same information through the
> kernel message added by "[PATCH v13 2/6] iommu: Print strict or lazy
> mode at init time".
I think that the print from 2/6 should occur before this print.
Regardless I would think that you would still like to be notified of
this change in policy, right?
However I now realize that the print is in a loop per iommu, so we would
get it per iommu:
for_each_active_iommu(iommu, drhd) {
/*
* The flush queue implementation does not perform
* page-selective invalidations that are required for efficient
* TLB flushes in virtual environments. The benefit of batching
* is likely to be much lower than the overhead of synchronizing
* the virtual and physical IOMMU page-tables.
*/
if (!intel_iommu_strict && cap_caching_mode(iommu->cap)) {
pr_warn("IOMMU batching is disabled due to virtualization");
intel_iommu_strict = 1;
}
...
}
I need to change that. How about this:
bool print_warning = false;
for_each_active_iommu(iommu, drhd) {
/*
* The flush queue implementation does not perform
* page-selective invalidations that are required for efficient
* TLB flushes in virtual environments. The benefit of batching
* is likely to be much lower than the overhead of synchronizing
* the virtual and physical IOMMU page-tables.
*/
if (!print_warning && cap_caching_mode(iommu->cap)) {
pr_warn("IOMMU batching disallowed due to virtualization\n");
iommu_set_dma_strict(true);
print_warning = true;
}
...
}
or use pr_warn_once().
Thanks,
John
next prev parent reply other threads:[~2021-06-17 8:06 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-16 11:03 [PATCH v13 0/6] iommu: Enhance IOMMU default DMA mode build options John Garry
2021-06-16 11:03 ` [PATCH v13 1/6] iommu: Deprecate Intel and AMD cmdline methods to enable strict mode John Garry
2021-06-17 19:01 ` Robin Murphy
2021-06-18 7:43 ` John Garry
2021-06-16 11:03 ` [PATCH v13 2/6] iommu: Print strict or lazy mode at init time John Garry
2021-06-16 11:03 ` [PATCH v13 3/6] iommu: Enhance IOMMU default DMA mode build options John Garry
2021-06-16 11:03 ` [PATCH v13 4/6] iommu/vt-d: Add support for " John Garry
2021-06-17 7:32 ` Lu Baolu
2021-06-17 8:00 ` John Garry [this message]
2021-06-17 19:03 ` Robin Murphy
2021-06-18 1:46 ` Lu Baolu
2021-06-18 7:31 ` John Garry
2021-06-16 11:03 ` [PATCH v13 5/6] iommu/amd: " John Garry
2021-06-16 11:03 ` [PATCH v13 6/6] iommu: Remove mode argument from iommu_set_dma_strict() John Garry
2021-06-17 7:36 ` Lu Baolu
2021-06-17 7:41 ` John Garry
2021-06-18 1:52 ` Lu Baolu
2021-06-17 18:56 ` Robin Murphy
2021-06-18 1:51 ` Lu Baolu
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