Re: [PATCH for-7.1] vfio/common: remove spurious tpm-crb-cmd misalignment warning

[Alex Williamson]

On Wed, 16 Mar 2022 21:29:51 +0100
Eric Auger <eric.auger@redhat.com> wrote:

> The CRB command buffer currently is a RAM MemoryRegion and given
> its base address alignment, it causes an error report on
> vfio_listener_region_add(). This region could have been a RAM device
> region, easing the detection of such safe situation but this option
> was not well received. So let's add a helper function that uses the
> memory region name to recognize the region and detect the situation
> is safe wrt assignment. Other regions can be listed here if such kind
> of problem occurs again.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
>  hw/vfio/common.c     | 26 +++++++++++++++++++++++++-
>  hw/vfio/trace-events |  1 +
>  2 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 080046e3f51..b58a38f5c57 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -861,6 +861,22 @@ static void 
> vfio_unregister_ram_discard_listener(VFIOContainer *container,
>      g_free(vrdl);
>  }
>  
> +static bool vfio_known_safe_misalignment(MemoryRegionSection *section)
> +{
> +    MemoryRegion *mr = section->mr;
> +
> +    if (strcmp(memory_region_name(mr), "tpm-crb-cmd") != 0) {
> +        return false;
> +    }

Hi Eric,

I was thinking more along the lines that we could use
memory_region_owner() to get the owning Object, then on
that we could maybe use INTERFACE_CHECK to look for TYPE_MEMORY_DEVICE,
then consider anything else optional.  (a) could something like that
work and (b) do all required mappings currently expose that interface?
Thanks,

Alex


> +
> +    /* this is a known safe misaligned region, just trace for debug purpose 
> */
> +    trace_vfio_known_safe_misalignment(memory_region_name(mr),
> +                                       section->offset_within_address_space,
> +                                       section->offset_within_region,
> +                                       qemu_real_host_page_size);
> +    return true;
> +}
> +
>  static void vfio_listener_region_add(MemoryListener *listener,
>                                       MemoryRegionSection *section)
>  {
> @@ -884,7 +900,15 @@ static void vfio_listener_region_add(MemoryListener 
> *listener,
>      if (unlikely((section->offset_within_address_space &
>                    ~qemu_real_host_page_mask) !=
>                   (section->offset_within_region & 
> ~qemu_real_host_page_mask))) {
> -        error_report("%s received unaligned region", __func__);
> +        if (!vfio_known_safe_misalignment(section)) {
> +            error_report("%s received unaligned region %s iova=0x%"PRIx64
> +                         " offset_within_region=0x%"PRIx64
> +                         " qemu_real_host_page_mask=0x%"PRIxPTR,
> +                         __func__, memory_region_name(section->mr),
> +                         section->offset_within_address_space,
> +                         section->offset_within_region,
> +                         qemu_real_host_page_mask);
> +        }
>          return;
>      }
>  
> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> index 0ef1b5f4a65..6f38a2e6991 100644
> --- a/hw/vfio/trace-events
> +++ b/hw/vfio/trace-events
> @@ -100,6 +100,7 @@ vfio_listener_region_add_skip(uint64_t start, uint64_t 
> end) "SKIPPING region_add
>  vfio_spapr_group_attach(int groupfd, int tablefd) "Attached groupfd %d to 
> liobn fd %d"
>  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_known_safe_misalignment(const char *name, uint64_t iova, uint64_t 
> offset_within_region, uint64_t page_size) "Region \"%s\" iova=0x%"PRIx64" 
> offset_within_region=0x%"PRIx64" qemu_real_host_page_mask=0x%"PRIxPTR ": 
> cannot be mapped for DMA"
>  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