From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
robin.murphy@arm.com, will@kernel.org, joro@8bytes.org,
darren@os.amperecomputing.com, scott@os.amperecomputing.com
Subject: Re: [PATCH] iommu/arm-smmu-v3: Enable PCI ATS in passthrough mode as well
Date: Fri, 3 Feb 2023 12:00:16 +0000 [thread overview]
Message-ID: <Y9z3UG+wEBn4i3G2@myrica> (raw)
In-Reply-To: <20230202124053.848792-1-gankulkarni@os.amperecomputing.com>
On Thu, Feb 02, 2023 at 04:40:53AM -0800, Ganapatrao Kulkarni wrote:
> The current smmu-v3 driver does not enable PCI ATS for physical functions
> of ATS capable End Points when booted in smmu bypass mode
> (iommu.passthrough=1). This will not allow virtual functions to enable
> ATS(even though EP supports it) while they are attached to a VM using
> VFIO driver.
>
> This patch adds changes to enable ATS support for physical functions
> in passthrough/bypass mode as well.
[...]
> @@ -2453,8 +2458,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>
> master->domain = smmu_domain;
>
> - if (smmu_domain->stage != ARM_SMMU_DOMAIN_BYPASS)
> - master->ats_enabled = arm_smmu_ats_supported(master);
> + master->ats_enabled = arm_smmu_ats_supported(master);
I should have added a comment for this. Only found the reason in an old
cover letter [1]:
"When no translation stages are enabled (0b100), ATS Translation Requests
(and Translated traffic, if SMMU_CR0.ATSCHK == 1) are denied as though
EATS == 0b00; the actual value of the EATS field is IGNORED. Such a
Translation Request causes F_BAD_ATS_TREQ and Translated traffic causes
F_TRANSL_FORBIDDEN."
(See 3.9.1.1 "Responses to ATS Translation Requests and Translated
transactions" and 5.2 "Stream Table Entry")
So I don't think we can enable ATS for bypass domains :/ The PF needs to
be in translated mode in that case.
I can send a patch adding the comment next cycle.
Thanks,
Jean
[1] https://lore.kernel.org/linux-iommu/20190409165245.26500-1-jean-philippe.brucker@arm.com/
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next prev parent reply other threads:[~2023-02-03 12:01 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-02 12:40 [PATCH] iommu/arm-smmu-v3: Enable PCI ATS in passthrough mode as well Ganapatrao Kulkarni
2023-02-02 13:22 ` Robin Murphy
2023-02-03 10:44 ` Ganapatrao Kulkarni
2023-02-03 12:12 ` Robin Murphy
2023-02-03 12:00 ` Jean-Philippe Brucker [this message]
2023-02-03 12:05 ` Will Deacon
2023-02-06 17:20 ` Ganapatrao Kulkarni
2023-02-06 19:45 ` Jean-Philippe Brucker
2023-02-07 9:50 ` Ganapatrao Kulkarni
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