linux-kernel - Re: [PATCH v2 1/2] vfio: introduce vfio_dma

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Date:   Thu, 16 Jan 2020 02:30:52 +0000
From:   Mika Penttilä <mika.penttila@...tfour.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Yan Zhao <yan.y.zhao@...el.com>
CC:     "zhenyuw@...ux.intel.com" <zhenyuw@...ux.intel.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "kevin.tian@...el.com" <kevin.tian@...el.com>,
        "peterx@...hat.com" <peterx@...hat.com>
Subject: Re: [PATCH v2 1/2] vfio: introduce vfio_dma_rw to read/write a range
 of IOVAs



On 15.1.2020 22.06, Alex Williamson wrote:
> On Tue, 14 Jan 2020 22:53:03 -0500
> Yan Zhao <yan.y.zhao@...el.com> wrote:
>
>> vfio_dma_rw will read/write a range of user space memory pointed to by
>> IOVA into/from a kernel buffer without pinning the user space memory.
>>
>> TODO: mark the IOVAs to user space memory dirty if they are written in
>> vfio_dma_rw().
>>
>> Cc: Kevin Tian <kevin.tian@...el.com>
>> Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
>> ---
>>   drivers/vfio/vfio.c             | 45 +++++++++++++++++++
>>   drivers/vfio/vfio_iommu_type1.c | 76 +++++++++++++++++++++++++++++++++
>>   include/linux/vfio.h            |  5 +++
>>   3 files changed, 126 insertions(+)
>>
>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
>> index c8482624ca34..8bd52bc841cf 100644
>> --- a/drivers/vfio/vfio.c
>> +++ b/drivers/vfio/vfio.c
>> @@ -1961,6 +1961,51 @@ int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn, int npage)
>>   }
>>   EXPORT_SYMBOL(vfio_unpin_pages);
>>   
>> +/*
>> + * Read/Write a range of IOVAs pointing to user space memory into/from a kernel
>> + * buffer without pinning the user space memory
>> + * @dev [in]  : device
>> + * @iova [in] : base IOVA of a user space buffer
>> + * @data [in] : pointer to kernel buffer
>> + * @len [in]  : kernel buffer length
>> + * @write     : indicate read or write
>> + * Return error code on failure or 0 on success.
>> + */
>> +int vfio_dma_rw(struct device *dev, dma_addr_t iova, void *data,
>> +		   size_t len, bool write)
>> +{
>> +	struct vfio_container *container;
>> +	struct vfio_group *group;
>> +	struct vfio_iommu_driver *driver;
>> +	int ret = 0;

Do you know the iova given to vfio_dma_rw() is indeed a gpa and not iova 
from a iommu mapping? So isn't it you actually assume all the guest is 
pinned,
like from device assignment?

Or who and how is the vfio mapping added before the vfio_dma_rw() ?

Thanks,
Mika