linux-kernel - Re: [PATCH v2 04/10] iommu/vt-d: Match CPU and IOMMU paging mode

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Date:   Tue, 19 Nov 2019 09:04:10 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>, Yi Liu <yi.l.liu@...el.com>
Subject: Re: [PATCH v2 04/10] iommu/vt-d: Match CPU and IOMMU paging mode

Hi Lu, Jacob,

On 11/19/19 4:06 AM, Lu Baolu wrote:
> Hi Eric and Jacob,
> 
> On 11/19/19 5:52 AM, Jacob Pan wrote:
>> On Mon, 18 Nov 2019 21:55:03 +0100
>> Auger Eric <eric.auger@...hat.com> wrote:
>>
>>> Hi Jacob,
>>>
>>> On 11/18/19 8:42 PM, Jacob Pan wrote:
>>>> When setting up first level page tables for sharing with CPU, we
>>>> need to ensure IOMMU can support no less than the levels supported
>>>> by the CPU.
>>>> It is not adequate, as in the current code, to set up 5-level paging
>>>> in PASID entry First Level Paging Mode(FLPM) solely based on CPU.
>>>>
>>>> Fixes: 437f35e1cd4c8 ("iommu/vt-d: Add first level page table
>>>> interface")
>>>> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>>>> Acked-by: Lu Baolu <baolu.lu@...ux.intel.com>
>>>> ---
>>>>   drivers/iommu/intel-pasid.c | 12 ++++++++++--
>>>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/iommu/intel-pasid.c
>>>> b/drivers/iommu/intel-pasid.c index 040a445be300..e7cb0b8a7332
>>>> 100644 --- a/drivers/iommu/intel-pasid.c
>>>> +++ b/drivers/iommu/intel-pasid.c
>>>> @@ -499,8 +499,16 @@ int intel_pasid_setup_first_level(struct
>>>> intel_iommu *iommu, }
>>>>     #ifdef CONFIG_X86
>>>> -    if (cpu_feature_enabled(X86_FEATURE_LA57))
>>>> -        pasid_set_flpm(pte, 1);
>>>> +    /* Both CPU and IOMMU paging mode need to match */
>>>> +    if (cpu_feature_enabled(X86_FEATURE_LA57)) {
>>>> +        if (cap_5lp_support(iommu->cap)) {
>>>> +            pasid_set_flpm(pte, 1);
>>>> +        } else {
>>>> +            pr_err("VT-d has no 5-level paging support
>>>> for CPU\n");
>>>> +            pasid_clear_entry(pte);
>>>> +            return -EINVAL;
>>> Can it happen? If I am not wrong intel_pasid_setup_first_level() only
>>> seems to be called from intel_svm_bind_mm which now checks the
>>> SVM_CAPABLE flag.
>>>
>> You are right, this check is not needed any more. I will drop the patch.
>>> Thanks
> 
> I'd suggest to keep this. This helper is not only for svm, although
> currently svm is the only caller. For first level pasid setup, let's
> set an assumption that hardware should never report mismatching paging
> modes, this is helpful especially when running vIOMMU in VM guests.

OK. So maybe just add the rationale in the commit message?

Thanks

Eric
> 
> Best regards,
> baolu
>