Re: [PATCH 16/17] Handle PCIe ECAM space access from guests

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Mar 13, 2026 at 04:35:05PM +0000, Thierry Escande wrote:
> This patch adds the logic to decode MMIO-based PCIe ECAM accesses. If
> the IOREQ_TYPE_COPY request is within the ECAM address space configured
> by hvmloader, the ioreq type is set to XEN_DMOP_IO_RANGE_PCI and the
> sbdf decoded from the accessed address.
> 
> Signed-off-by: Thierry Escande <thierry.escande@xxxxxxxxxx>
> ---
>  xen/arch/x86/hvm/ioreq.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/ioreq.c b/xen/arch/x86/hvm/ioreq.c
> index a5fa97e149..022fe05222 100644
> --- a/xen/arch/x86/hvm/ioreq.c
> +++ b/xen/arch/x86/hvm/ioreq.c
> @@ -268,6 +268,8 @@ bool arch_ioreq_server_get_type_addr(const struct domain 
> *d,
>                                       uint64_t *addr)
>  {
>      unsigned int cf8 = d->arch.hvm.pci_cf8;
> +    unsigned long mmio_start = (p->type == IOREQ_TYPE_COPY) ?
> +                                ioreq_mmio_first_byte(p) : 0;
>  
>      if ( p->type != IOREQ_TYPE_COPY && p->type != IOREQ_TYPE_PIO )
>          return false;
> @@ -298,6 +300,19 @@ bool arch_ioreq_server_get_type_addr(const struct domain 
> *d,
>                  *addr |= CF8_ADDR_HI(cf8);
>          }
>      }
> +    else if ( p->type == IOREQ_TYPE_COPY &&
> +              (mmio_start >= d->arch.ecam_addr &&
> +               mmio_start < (d->arch.ecam_addr + d->arch.ecam_size)) )
> +    {
> +        pci_sbdf_t sbdf;
> +        unsigned int reg = mmio_start & ~PAGE_MASK;
> +
> +        sbdf.bdf =  (((mmio_start - d->arch.ecam_addr) & 0x0ffff000) >> 12);
> +        sbdf.seg = 0;
> +
> +        *type = XEN_DMOP_IO_RANGE_PCI;
> +        *addr = ((uint64_t)sbdf.sbdf << 32) | reg;

The trapping & decoding here should better re-use the logic in the
vpci_mmcfg* handlers in x86/hvm/io.c.  You might want to gate the call
to register_mmio_handler() to the domain having vPCI, so that
otherwise it will be handled by the IOREQ catch-all.  It's a bit
hacky, but we already know that vPCI and IOREQs don't play well, and
it needs solving properly.  Again I don't want to force you having to
do that just to get q35 merged.  But we should at least aim to not
duplicate the data in the domain structures.

Thanks, Roger.