linux-kernel - Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT

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Message-ID: <91e61165-6695-4948-9a38-79c1b1e6305c@intel.com>
Date:   Tue, 28 Nov 2023 13:54:45 +0800
From:   Yi Liu <yi.l.liu@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        Baolu Lu <baolu.lu@...ux.intel.com>
CC:     <joro@...tes.org>, <alex.williamson@...hat.com>, <jgg@...dia.com>,
        <kevin.tian@...el.com>, <robin.murphy@....com>,
        <cohuck@...hat.com>, <eric.auger@...hat.com>,
        <kvm@...r.kernel.org>, <mjrosato@...ux.ibm.com>,
        <chao.p.peng@...ux.intel.com>, <yi.y.sun@...ux.intel.com>,
        <peterx@...hat.com>, <jasowang@...hat.com>,
        <shameerali.kolothum.thodi@...wei.com>, <lulu@...hat.com>,
        <suravee.suthikulpanit@....com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        <zhenzhong.duan@...el.com>, <joao.m.martins@...cle.com>,
        <xin.zeng@...el.com>, <yan.y.zhao@...el.com>
Subject: Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

On 2023/11/21 13:19, Nicolin Chen wrote:
> On Tue, Nov 21, 2023 at 01:02:49PM +0800, Baolu Lu wrote:
>> On 11/17/23 9:07 PM, Yi Liu wrote:
>>> In nested translation, the stage-1 page table is user-managed but cached
>>> by the IOMMU hardware, so an update on present page table entries in the
>>> stage-1 page table should be followed with a cache invalidation.
>>>
>>> Add an IOMMU_HWPT_INVALIDATE ioctl to support such a cache invalidation.
>>> It takes hwpt_id to specify the iommu_domain, and a multi-entry array to
>>> support multiple invalidation requests in one ioctl.
>>>
>>> Check cache_invalidate_user op in the iommufd_hw_pagetable_alloc_nested,
>>> since all nested domains need that.
>>>
>>> Co-developed-by: Nicolin Chen<nicolinc@...dia.com>
>>> Signed-off-by: Nicolin Chen<nicolinc@...dia.com>
>>> Signed-off-by: Yi Liu<yi.l.liu@...el.com>
>>> ---
>>>    drivers/iommu/iommufd/hw_pagetable.c    | 35 +++++++++++++++++++++++++
>>>    drivers/iommu/iommufd/iommufd_private.h |  9 +++++++
>>>    drivers/iommu/iommufd/main.c            |  3 +++
>>>    include/uapi/linux/iommufd.h            | 35 +++++++++++++++++++++++++
>>>    4 files changed, 82 insertions(+)
>>>
>>> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
>>> index 2abbeafdbd22..367459d92f69 100644
>>> --- a/drivers/iommu/iommufd/hw_pagetable.c
>>> +++ b/drivers/iommu/iommufd/hw_pagetable.c
>>> @@ -238,6 +238,11 @@ iommufd_hwpt_nested_alloc(struct iommufd_ctx *ictx,
>>>                rc = -EINVAL;
>>>                goto out_abort;
>>>        }
>>> +     /* Driver is buggy by missing cache_invalidate_user in domain_ops */
>>> +     if (WARN_ON_ONCE(!hwpt->domain->ops->cache_invalidate_user)) {
>>> +             rc = -EINVAL;
>>> +             goto out_abort;
>>> +     }
>>>        return hwpt_nested;
>>
>> The WARN message here may cause kernel regression when users bisect
>> issues. Till this patch, there are no drivers support the
>> cache_invalidation_user callback yet.
> 
> Ah, this is an unintended consequence from our uAPI bisect to
> merge the nesting alloc first...
> 
> Would removing the WARN_ON_ONCE be okay? Although having this
> WARN is actually the point here...

seems like we may need to remove it. how about your opinion, @Jason?

> Thanks
> Nic

-- 
Regards,
Yi Liu