Re: [dpdk-dev] [PATCH v2 5/7] mem: modify error message for DMA mask check

[Alejandro Lucero <alejandro.lucero@netronome.com>]

On Tue, Nov 6, 2018 at 10:31 AM Burakov, Anatoly <anatoly.burakov@intel.com>
wrote:

> On 06-Nov-18 9:32 AM, Alejandro Lucero wrote:
> >
> >
> > On Mon, Nov 5, 2018 at 4:35 PM Burakov, Anatoly
> > <anatoly.burakov@intel.com <mailto:anatoly.burakov@intel.com>> wrote:
> >
> >     On 05-Nov-18 3:33 PM, Alejandro Lucero wrote:
> >      >
> >      >
> >      > On Mon, Nov 5, 2018 at 3:12 PM Burakov, Anatoly
> >      > <anatoly.burakov@intel.com <mailto:anatoly.burakov@intel.com>
> >     <mailto:anatoly.burakov@intel.com
> >     <mailto:anatoly.burakov@intel.com>>> wrote:
> >      >
> >      >     On 05-Nov-18 10:13 AM, Alejandro Lucero wrote:
> >      >      > On Mon, Nov 5, 2018 at 10:01 AM Li, WenjieX A
> >      >     <wenjiex.a.li@intel.com <mailto:wenjiex.a.li@intel.com>
> >     <mailto:wenjiex.a.li@intel.com <mailto:wenjiex.a.li@intel.com>>>
> >      >      > wrote:
> >      >      >
> >      >      >> 1. With GCC32, testpmd could not startup without
> >     '--iova-mode pa'.
> >      >      >> ./i686-native-linuxapp-gcc/app/testpmd -c f -n 4 -- -i
> >      >      >> The output is:
> >      >      >> EAL: Detected 16 lcore(s)
> >      >      >> EAL: Detected 1 NUMA nodes
> >      >      >> EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
> >      >      >> EAL: Some devices want iova as va but pa will be used
> >     because..
> >      >     EAL: few
> >      >      >> device bound to UIO
> >      >      >> EAL: No free hugepages reported in hugepages-1048576kB
> >      >      >> EAL: Probing VFIO support...
> >      >      >> EAL: VFIO support initialized
> >      >      >> EAL: wrong dma mask size 48 (Max: 31)
> >      >      >> EAL: alloc_pages_on_heap(): couldn't allocate memory due
> >     to IOVA
> >      >     exceeding
> >      >      >> limits of current DMA mask
> >      >      >> error allocating rte services array
> >      >      >> EAL: FATAL: rte_service_init() failed
> >      >      >> EAL: rte_service_init() failed
> >      >      >> PANIC in main():
> >      >      >> Cannot init EAL
> >      >      >> 5: [./i686-native-linuxapp-gcc/app/testpmd(+0x95fda)
> >     [0x56606fda]]
> >      >      >> 4: [/lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf6)
> >      >     [0xf74d1276]]
> >      >      >> 3: [./i686-native-linuxapp-gcc/app/testpmd(main+0xf21)
> >     [0x565fcee1]]
> >      >      >> 2:
> [./i686-native-linuxapp-gcc/app/testpmd(__rte_panic+0x3d)
> >      >     [0x565edc68]]
> >      >      >> 1:
> >     [./i686-native-linuxapp-gcc/app/testpmd(rte_dump_stack+0x33)
> >      >      >> [0x5675f333]]
> >      >      >> Aborted
> >      >      >>
> >      >      >> 2. With '--iova-mode pa', testpmd could startup.
> >      >      >> 3. With GCC64, there is no such issue.
> >      >      >> Thanks!
> >      >      >>
> >      >      >>
> >      >      > Does 32 bits support require IOMMU? It would be a
> surprise. If
> >      >     there is no
> >      >      > IOMMU hardware, no dma mask should be there at all.
> >      >
> >      >     IOMMU is supported on 32-bits, however limited the address
> >     space might
> >      >     be. Maybe limit IOMMU width to RTE_MIN(31, value) bits for
> >      >     everything on
> >      >     32-bit?
> >      >
> >      >
> >      > If IOMMU is supported in 32 bits, then the DMA mask check should
> >     not be
> >      > happening. AFAIK, the IOMMU hardware addressing limitations is a
> >     problem
> >      > only in 64 bits systems. The worst situation I have head of is 39
> >     bits
> >      > for virtualized IOMMU with QEMU.
> >      >
> >      > I would prefer not to invoke rte_mem_set_dma_mask for 32 bits
> >     system for
> >      > the Intel IOMMU case. The only other dma mask client is the NFP
> >     PMD and
> >      > we do not support 32 bits systems.
> >      >
> >
> >     I don't think not invoking DMA mask check is the right choice here.
> In
> >     practice it may be, but i'd rather the behavior to be "correct", if
> at
> >     all possible :) It is theoretically possible to have an IOMMU with an
> >     addressing limitation of, say, 30 bits (even though they don't exist
> in
> >     reality), so therefore our code should handle it, should it encounter
> >     one, and it should also handle the "proper" ones correctly (as in,
> >     treat
> >     them as 32-bit-limited instead of 39- or 48-bit-limited).
> >
> >
> > Fine.
> >
> > The problem is the current sanity check about the dma mask width, what
> > is 31 for 32 bits systems.
> > Should we just leave a single max dma width to 63? This covers the
> > possibility of 32 bit systems integrating an IOMMU designed for  64
> > bits. I really doubt this is a real possibility in x86, although I can
> > see it more likely in embedded systems where this sort of hardware
> > components integration happens.
>
> Actually (and after a quick chat with Ferruh), is this even needed? IOVA
> addresses are independent from VA width, IOVA can happily be bigger than
> 32-bits if i understand things correctly. All of our IOVA addresses are
> always 64-bit throughout DPDK. I don't think this check is even valid.
>
>
Although iova_t is 64 bits, there should not be a IOVA higher than 32 bits,
although there could be exceptions like PAE extensions (I'm old enough for
remembering that option :-( ).

Anyway, the original idea of dma mask sanity check is 32 bits systems was
assuming there should not be a dma mask above 32 bits, but I'm happy with
removing that sanity check for 32 bits systems. So, do you agree to just
leave the sanity check for a max width of 63 bits?


> >
> >      >
> >      >     --
> >      >     Thanks,
> >      >     Anatoly
> >      >
> >
> >
> >     --
> >     Thanks,
> >     Anatoly
> >
>
>
> --
> Thanks,
> Anatoly
>