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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

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>> 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>>
>      > 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).

> 
>     -- 
>     Thanks,
>     Anatoly
> 


-- 
Thanks,
Anatoly