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 11:06:10 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Auger Eric <eric.auger@...hat.com>
Cc:     baolu.lu@...ux.intel.com, 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 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.

Best regards,
baolu