Re: [PATCH] vfio/listener: Only warn on misalignment for VFIO-owned regions

[Alex Williamson <alex@shazbot.org>]

On Thu,  2 Jul 2026 18:06:40 +0200
Cédric Le Goater <clg@redhat.com> wrote:

> Any device on the board can have non-page-aligned memory regions. The
> VFIO listener should not warn about misalignment for regions that are
> not VFIO-related.
> 
> Replace the vfio_known_safe_misalignment() whitelist with a
> vfio_get_vfio_device() ownership check: only warn when a VFIO device's
> own region is misaligned. For all other regions, emit a trace event
> and silently skip. Extract the misalignment test into a
> vfio_section_misaligned() helper for readability.
> 
> Note: vfio_get_vfio_device() currently only covers VFIO PCI devices,
> including vfio-user-pci.  Other VFIO backends (AP, CCW) don't expose
> memory regions through this path so this is sufficient for now.

I thought the whole point was to warn when there are non-vfio devices
that we cannot insert into the DMA map.  851d6d1a0ff2 added tpm-crb-cmd
to an ignore list because it's not a DMA target.  The intention of that
ignore list was to continue to evaluate devices that are misaligned
and either add them to the ignore list or determine they could be a
valid DMA target and correct the alignment.

Can this even legitimately trigger with a vfio-pci device?  Thanks,

Alex

> 
> Suggested-by: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Cédric Le Goater <clg@redhat.com>
> ---
>  hw/vfio/device.c     |  2 +-
>  hw/vfio/listener.c   | 33 +++++++++++++++------------------
>  hw/vfio/trace-events |  2 +-
>  3 files changed, 17 insertions(+), 20 deletions(-)
> 
> diff --git a/hw/vfio/device.c b/hw/vfio/device.c
> index 1a7f8088aad9583ee96fc303be917fdb2f100df9..3a47109efb35c6dc28719dcc19acb85bef1d26cd 100644
> --- a/hw/vfio/device.c
> +++ b/hw/vfio/device.c
> @@ -439,7 +439,7 @@ bool vfio_device_hiod_create_and_realize(VFIODevice *vbasedev,
>  
>  VFIODevice *vfio_get_vfio_device(Object *obj)
>  {
> -    if (object_dynamic_cast(obj, TYPE_VFIO_PCI)) {
> +    if (object_dynamic_cast(obj, TYPE_VFIO_PCI_DEVICE)) {
>          return &VFIO_PCI_DEVICE(obj)->vbasedev;
>      } else {
>          return NULL;
> diff --git a/hw/vfio/listener.c b/hw/vfio/listener.c
> index c19600e980a8d02217b5d9df4aca8f879ab2c5d5..76b9b02f8163f18d20994e4ec1f914a4d148fa92 100644
> --- a/hw/vfio/listener.c
> +++ b/hw/vfio/listener.c
> @@ -40,7 +40,6 @@
>  #include "migration/misc.h"
>  #include "migration/qemu-file.h"
>  #include "system/tcg.h"
> -#include "system/tpm.h"
>  #include "vfio-migration-internal.h"
>  #include "vfio-helpers.h"
>  #include "vfio-listener.h"
> @@ -352,20 +351,10 @@ static void vfio_ram_discard_unregister_listener(VFIOContainer *bcontainer,
>      g_free(vrdl);
>  }
>  
> -static bool vfio_known_safe_misalignment(MemoryRegionSection *section)
> +static bool vfio_section_misaligned(MemoryRegionSection *section)
>  {
> -    MemoryRegion *mr = section->mr;
> -
> -    if (!TPM_IS_CRB(mr->owner)) {
> -        return false;
> -    }
> -
> -    /* 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;
> +    return (section->offset_within_address_space & ~qemu_real_host_page_mask()) !=
> +           (section->offset_within_region & ~qemu_real_host_page_mask());
>  }
>  
>  static bool vfio_listener_valid_section(MemoryRegionSection *section,
> @@ -379,10 +368,12 @@ static bool vfio_listener_valid_section(MemoryRegionSection *section,
>          return false;
>      }
>  
> -    if (unlikely((section->offset_within_address_space &
> -                  ~qemu_real_host_page_mask()) !=
> -                 (section->offset_within_region & ~qemu_real_host_page_mask()))) {
> -        if (!vfio_known_safe_misalignment(section)) {
> +    if (unlikely(vfio_section_misaligned(section))) {
> +        /*
> +         * Only warn for VFIO device regions.  Other VFIO backends
> +         * (AP, CCW) don't expose memory regions through this path.
> +         */
> +        if (vfio_get_vfio_device(memory_region_owner(section->mr))) {
>              error_report("%s received unaligned region %s iova=0x%"PRIx64
>                           " offset_within_region=0x%"PRIx64
>                           " qemu_real_host_page_size=0x%"PRIxPTR,
> @@ -390,6 +381,12 @@ static bool vfio_listener_valid_section(MemoryRegionSection *section,
>                           section->offset_within_address_space,
>                           section->offset_within_region,
>                           qemu_real_host_page_size());
> +        } else {
> +            trace_vfio_listener_region_misaligned(
> +                         memory_region_name(section->mr),
> +                         section->offset_within_address_space,
> +                         section->offset_within_region,
> +                         qemu_real_host_page_size());
>          }
>          return false;
>      }
> diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
> index f71d0bbc0a5440e4ccd374fac4733af08438e7be..5056b9942027938cd6bc832198acc9809739399f 100644
> --- a/hw/vfio/trace-events
> +++ b/hw/vfio/trace-events
> @@ -98,7 +98,7 @@ vfio_spapr_group_attach(int groupfd, int tablefd) "Attached groupfd %d to liobn
>  vfio_listener_region_add_iommu(const char* name, uint64_t start, uint64_t end) "region_add [iommu] %s 0x%"PRIx64" - 0x%"PRIx64
>  vfio_listener_region_del_iommu(const char *name) "region_del [iommu] %s"
>  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, uintptr_t page_size) "Region \"%s\" iova=0x%"PRIx64" offset_within_region=0x%"PRIx64" qemu_real_host_page_size=0x%"PRIxPTR
> +vfio_listener_region_misaligned(const char *name, uint64_t iova, uint64_t offset_within_region, uintptr_t page_size) "Region \"%s\" iova=0x%"PRIx64" offset_within_region=0x%"PRIx64" qemu_real_host_page_size=0x%"PRIxPTR
>  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_skip_dma_map(const char *name, uint64_t iova, uint64_t size) "Region \"%s\" 0x%"PRIx64" size=0x%"PRIx64" marked to skip IOMMU mapping"
>  vfio_listener_region_del(uint64_t start, uint64_t end) "region_del 0x%"PRIx64" - 0x%"PRIx64