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
WARNING: multiple messages have this Message-ID (diff)
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-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, iommu@lists.linux-foundation.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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2021-06-17 8:06 UTC|newest] Thread overview: 38+ 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 ` John Garry 2021-06-16 11:03 ` [PATCH v13 1/6] iommu: Deprecate Intel and AMD cmdline methods to enable strict mode John Garry 2021-06-16 11:03 ` John Garry 2021-06-17 19:01 ` Robin Murphy 2021-06-17 19:01 ` Robin Murphy 2021-06-18 7:43 ` John Garry 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 ` 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 ` John Garry 2021-06-16 11:03 ` [PATCH v13 4/6] iommu/vt-d: Add support for " John Garry 2021-06-16 11:03 ` John Garry 2021-06-17 7:32 ` Lu Baolu 2021-06-17 7:32 ` Lu Baolu 2021-06-17 8:00 ` John Garry [this message] 2021-06-17 8:00 ` John Garry 2021-06-17 19:03 ` Robin Murphy 2021-06-17 19:03 ` Robin Murphy 2021-06-18 1:46 ` Lu Baolu 2021-06-18 1:46 ` Lu Baolu 2021-06-18 7:31 ` John Garry 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 ` John Garry 2021-06-16 11:03 ` [PATCH v13 6/6] iommu: Remove mode argument from iommu_set_dma_strict() John Garry 2021-06-16 11:03 ` John Garry 2021-06-17 7:36 ` Lu Baolu 2021-06-17 7:36 ` Lu Baolu 2021-06-17 7:41 ` John Garry 2021-06-17 7:41 ` John Garry 2021-06-18 1:52 ` Lu Baolu 2021-06-18 1:52 ` Lu Baolu 2021-06-17 18:56 ` Robin Murphy 2021-06-17 18:56 ` Robin Murphy 2021-06-18 1:51 ` Lu Baolu 2021-06-18 1:51 ` Lu Baolu
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