Messages in this thread | | | Subject | Re: [PATCH v14 6/6] iommu: Remove mode argument from iommu_set_dma_strict() | From | John Garry <> | Date | Mon, 21 Jun 2021 13:08:51 +0100 |
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On 21/06/2021 12:59, Robin Murphy wrote:
+ Nadav
>> On a personal level I would be happy with that approach, but I think >> it's better to not start changing things right away in a follow-up series. >> >> So how about we add this patch (which replaces 6/6 "iommu: Remove mode >> argument from iommu_set_dma_strict()")? >> >> Robin, any opinion? > For me it boils down to whether there are any realistic workloads where > non-strict mode*would* still perform better under virtualisation. The > only reason for the user to explicitly pass "iommu.strict=0" is because > they expect it to increase unmap performance; if it's only ever going to > lead to an unexpected performance loss, I don't see any value in > overriding the kernel's decision purely for the sake of subservience. > > If there*are* certain valid cases for allowing it for people who really > know what they're doing, then we should arguably also log a counterpart > message to say "we're honouring your override but beware it may have the > opposite effect to what you expect" for the benefit of other users who > assume it's a generic go-faster knob. At that point it starts getting > non-trivial enough that I'd want to know for sure it's worthwhile. > > The other reason this might be better to revisit later is that an AMD > equivalent is still in flight[1], and there might be more that can > eventually be factored out. I think both series are pretty much good to > merge for 5.14, but time's already tight to sort out the conflicts which > exist as-is, without making them any worse.
ok, fine. Can revisit.
As for getting these merged, I'll dry-run merging both of those series to see the conflicts. It doesn't look too problematic from a glance.
Cheers, John
> > Robin. > > [1] > https://lore.kernel.org/linux-iommu/20210616100500.174507-3-namit@vmware.com/ > >> ------->8--------- >> >> [PATCH] iommu/vt-d: Make "iommu.strict" override batching due to >> virtualization >> >> As a change in policy, make iommu.strict cmdline argument override >> whether we disable batching due to virtualization. >> >> The API of iommu_set_dma_strict() is changed to accept a "force" >> argument, which means that we always set iommu_dma_strict true, >> regardless of whether we already set via cmdline. Also return a boolean, >> to tell whether iommu_dma_strict was set or not. >> >> Note that in all pre-existing callsites of iommu_set_dma_strict(), >> argument strict was true, so this argument is dropped. >> >> Signed-off-by: John Garry<john.garry@huawei.com> >> >> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c >> index 06666f9d8116..e8d65239b359 100644 >> --- a/drivers/iommu/intel/iommu.c >> +++ b/drivers/iommu/intel/iommu.c >> @@ -4380,10 +4380,8 @@ 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 (cap_caching_mode(iommu->cap)) { >> + if (cap_caching_mode(iommu->cap) && iommu_set_dma_strict(false)) >> pr_info_once("IOMMU batching disallowed due to >> virtualization\n"); >> - iommu_set_dma_strict(true); >> - } >> iommu_device_sysfs_add(&iommu->iommu, NULL, >> intel_iommu_groups, >> "%s", iommu->name); >> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >> index 60b1ec42e73b..1434bee64af3 100644 >> --- a/drivers/iommu/iommu.c >> +++ b/drivers/iommu/iommu.c >> @@ -349,10 +349,14 @@ static int __init iommu_dma_setup(char *str) >> } >> early_param("iommu.strict", iommu_dma_setup); >> >> -void iommu_set_dma_strict(bool strict) >> +/* Return true if we set iommu_dma_strict */ >> +bool iommu_set_dma_strict(bool force) >> { >> - if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT)) >> - iommu_dma_strict = strict; >> + if (force || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT)) { >> + iommu_dma_strict = true; >> + return true; >> + } >> + return false; >> } >> >> bool iommu_get_dma_strict(struct iommu_domain *domain) >> diff --git a/include/linux/iommu.h b/include/linux/iommu.h >> index 32d448050bf7..f17b20234296 100644 >> --- a/include/linux/iommu.h >> +++ b/include/linux/iommu.h >> @@ -476,7 +476,7 @@ int iommu_enable_nesting(struct iommu_domain *domain); >> int iommu_set_pgtable_quirks(struct iommu_domain *domain, >> unsigned long quirks); >> >> -void iommu_set_dma_strict(bool val); >> +bool iommu_set_dma_strict(bool force); >> bool iommu_get_dma_strict(struct iommu_domain *domain); >> >> extern int report_iommu_fault(struct iommu_domain *domain, struct >> device *dev,
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