Wednesday, February 13, 2019 11:59 AM, Gaëtan RiveT:
> Subject: Re: [PATCH 2/6] vfio: don't fail to DMA map if memory is already
> mapped
>
> On Wed, Feb 13, 2019 at 11:10:22AM +0200, Shahaf Shuler wrote:
> > Currently vfio DMA map function will fail in case the same memory
> > segment is mapped twice.
> >
> > This is too strict, as this is not an error to map the same memory
> > twice.
> >
> > Instead, use the kernel return value to detect such state and have the
> > DMA function to return as successful.
> >
> > For type1 mapping the kernel driver first implementation returns EBUSY
> > and since kernel 3.11 returns EEXISTS. For spapr mapping EBUSY is
> > returned since kernel 4.10.
> >
>
> What is the earliest version supported by DPDK? I thought 3.10 was dropped,
> should we care about the 3.11 return value?
According to DPDK doc it is 3.16, however compatibility for Centos/RH 7 should
be kept.
I have looked on Centos 7 source code (linux-3.10.0-957.5.1.el7), it uses
EEXIST for the vfio type 1.
So I think, I can drop the EBUSY error check and leave only the EEXIST one.
>
> > Signed-off-by: Shahaf Shuler <shah...@mellanox.com>
> > ---
> > lib/librte_eal/linuxapp/eal/eal_vfio.c | 12 ++++++++++--
> > 1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/librte_eal/linuxapp/eal/eal_vfio.c
> > b/lib/librte_eal/linuxapp/eal/eal_vfio.c
> > index 48ca9465d4..2a2d655b37 100644
> > --- a/lib/librte_eal/linuxapp/eal/eal_vfio.c
> > +++ b/lib/librte_eal/linuxapp/eal/eal_vfio.c
> > @@ -1263,7 +1263,11 @@ vfio_type1_dma_mem_map(int
> vfio_container_fd, uint64_t vaddr, uint64_t iova,
> > VFIO_DMA_MAP_FLAG_WRITE;
> >
> > ret = ioctl(vfio_container_fd, VFIO_IOMMU_MAP_DMA,
> &dma_map);
> > - if (ret) {
> > + /**
> > + * In case the mapping was already done EEXIST will be
> > + * returned from kernel.
> > + */
> > + if ((ret != -EEXIST) && (ret != -EBUSY)) {
>
> Won't a ret == 0 trigger the error then?
Yes good catch.
>
> It seems ifdef about linux versions are not common in vfio code, but bar that
> I think it would be cleaner to restrict the acceptable error to it.
>
> When a version will be dropped it will be much easier to remove the related
> code instead of digging in the commit logs, and leaving both would not be
> clean.
Relaying on kernel version is not safe enough. Many distro backport to their
kernel w/o updating its version. This will lead to unexpected behavior.
>
> > RTE_LOG(ERR, EAL, " cannot set up DMA remapping,
> error %i (%s)\n",
> > errno, strerror(errno));
> > return -1;
> > @@ -1324,7 +1328,11 @@ vfio_spapr_dma_do_map(int vfio_container_fd,
> uint64_t vaddr, uint64_t iova,
> > VFIO_DMA_MAP_FLAG_WRITE;
> >
> > ret = ioctl(vfio_container_fd, VFIO_IOMMU_MAP_DMA,
> &dma_map);
> > - if (ret) {
> > + /**
> > + * In case the mapping was already done EBUSY will be
> > + * returned from kernel.
> > + */
> > + if (ret != -EBUSY) {
> > RTE_LOG(ERR, EAL, " cannot set up DMA remapping,
> error %i (%s)\n",
> > errno, strerror(errno));
> > return -1;
> > --
> > 2.12.0
> >
>
> --
> Gaëtan Rivet
> 6WIND
