Re: [Qemu-devel] [PATCH v2 for 2.12] vfio: Use a trace point when a RAM section cannot be DMA mapped

[Alex Williamson <alex.williamson@redhat.com>]

On Wed,  4 Apr 2018 22:30:50 +0200
Eric Auger <eric.auger@redhat.com> wrote:

> The 567b5b309abe ("vfio/pci: Relax DMA map errors for MMIO regions")
> added an error message if a passed memory section address or size
> is not aligned to the page size and thus cannot be DMA mapped.
> 
> This patch fixes the trace by printing the region name and the
> memory region section offset within the address space (instead of
> offset_within_region).
> 
> We also turn the error_report into a trace event. Indeed, In some
> cases, the traces can be confusing to non expert end-users and
> let think the use case does not work (whereas it
> works as before).
> 
> This is the case where a BAR is successively mapped at different
> GPAs and its sections are not compatible with dma map. The listener
> is called several times and traces are issued for each intermediate
> mapping.  The end-user cannot easily match those GPAs against the
> final GPA output by lscpi. So let's keep those information to
> informed users. In mid term, the plan is to advise the user about
> BAR relocation relevance.
> 
> Fixes: 567b5b309abe "vfio/pci: Relax DMA map errors for MMIO regions"
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> 
> ---
> 
> v1 -> v2:
> - use a trace point
> - add some details in the commit message

I think this is v2 with v1 being
Message-Id:<20180322081837.21460-1-aik@ozlabs.ru> but this is
substantially different from Alexey's posting so I'd like to verify the
Sign-off.  Alexey?

I agree that this seems to be the right thing to do for 2.12, nothing
has changed for these mappings and the error reports are difficult even
for experts to decipher and explain to users.  Thanks,

Alex

> ---
>  hw/vfio/common.c     | 11 +++++------
>  hw/vfio/trace-events |  1 +
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 5e84716..07ffa0b 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -548,12 +548,11 @@ static void vfio_listener_region_add(MemoryListener *listener,
>          hwaddr pgmask = (1ULL << ctz64(hostwin->iova_pgsizes)) - 1;
>  
>          if ((iova & pgmask) || (int128_get64(llsize) & pgmask)) {
> -            error_report("Region 0x%"HWADDR_PRIx"..0x%"HWADDR_PRIx
> -                         " is not aligned to 0x%"HWADDR_PRIx
> -                         " and cannot be mapped for DMA",
> -                         section->offset_within_region,
> -                         int128_getlo(section->size),
> -                         pgmask + 1);
> +            trace_vfio_listener_region_add_no_dma_map(
> +                memory_region_name(section->mr),
> +                section->offset_within_address_space,
> +                int128_getlo(section->size),
> +                pgmask + 1);
>              return;
>          }
>      }
> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> index 79f63a2..20109cb 100644
> --- a/hw/vfio/trace-events
> +++ b/hw/vfio/trace-events
> @@ -90,6 +90,7 @@ vfio_iommu_map_notify(const char *op, uint64_t iova_start, uint64_t iova_end) "i
>  vfio_listener_region_add_skip(uint64_t start, uint64_t end) "SKIPPING region_add 0x%"PRIx64" - 0x%"PRIx64
>  vfio_listener_region_add_iommu(uint64_t start, uint64_t end) "region_add [iommu] 0x%"PRIx64" - 0x%"PRIx64
>  vfio_listener_region_add_ram(uint64_t iova_start, uint64_t iova_end, void *vaddr) "region_add [ram] 0x%"PRIx64" - 0x%"PRIx64" [%p]"
> +vfio_listener_region_add_no_dma_map(const char *name, uint64_t iova, uint64_t size, uint64_t page_size) "Region \"%s\" 0x%"PRIx64" size=0x%"PRIx64" is not aligned to 0x%"PRIx64" and cannot be mapped for DMA"
>  vfio_listener_region_del_skip(uint64_t start, uint64_t end) "SKIPPING region_del 0x%"PRIx64" - 0x%"PRIx64
>  vfio_listener_region_del(uint64_t start, uint64_t end) "region_del 0x%"PRIx64" - 0x%"PRIx64
>  vfio_disconnect_container(int fd) "close container->fd=%d"