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Message-ID: <ZM0FQW9qo3RoNKmX@nvidia.com>
Date: Fri, 4 Aug 2023 11:03:45 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: "Liu, Yi L" <yi.l.liu@...el.com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>,
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Subject: Re: [PATCH v4 07/12] iommufd: Add data structure for Intel VT-d
stage-1 cache invalidation
On Fri, Aug 04, 2023 at 01:04:57PM +0000, Liu, Yi L wrote:
> > > Having the driver copy in a loop might be better
> > >
> >
> > Can you elaborate?
>
> I think Jason means the way in patch 09.
Yeah, you can't reuse the stack buffer for an array, so patch 9 copies
each element uniquely.
This is more calls to copy_to_user, which has some cost
But we avoid a memory allocation
Patch 9 should not abuse the user_data, cast it to the inv_info and
just put req on the stack:
struct iommu_hwpt_vtd_s1_invalidate *inv_info = user_data;
struct iommu_hwpt_vtd_s1_invalidate_desc req;
But I'm not sure about this entry_size logic, what happens if the
entry_size is larger than the kernel supports? I think it should
fail..
Jason
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