Re: [PATCH v2 for 4.5] ioreq-server: handle the lack of a default emulator properly

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 29/09/14 11:21, Paul Durrant wrote:
> I started porting QEMU over to use the new ioreq server API and hit a
> problem with PCI bus enumeration. Because, with my patches, QEMU only
> registers to handle config space accesses for the PCI device it implements
> all other attempts by the guest to access 0xcfc go nowhere and this was
> causing the vcpu to wedge up because nothing was completing the I/O.
>
> This patch introduces an I/O completion handler into the hypervisor for the
> case where no ioreq server matches a particular request. Read requests are
> completed with 0xf's in the data buffer, writes and all other I/O req types
> are ignored.
>
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Cc: Keir Fraser <keir@xen.org>
> Cc: Jan Beulich <jbeulich@suse.com>
> ---
> v2: - First non-RFC submission
>     - Removed warning on unemulated MMIO accesses
>
>  xen/arch/x86/hvm/hvm.c |   35 ++++++++++++++++++++++++++++++++---
>  1 file changed, 32 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 5c7e0a4..822ac37 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -2386,8 +2386,7 @@ static struct hvm_ioreq_server *hvm_select_ioreq_server(struct domain *d,
>      if ( list_empty(&d->arch.hvm_domain.ioreq_server.list) )
>          return NULL;
>  
> -    if ( list_is_singular(&d->arch.hvm_domain.ioreq_server.list) ||
> -         (p->type != IOREQ_TYPE_COPY && p->type != IOREQ_TYPE_PIO) )
> +    if ( p->type != IOREQ_TYPE_COPY && p->type != IOREQ_TYPE_PIO )
>          return d->arch.hvm_domain.default_ioreq_server;
>  
>      cf8 = d->arch.hvm_domain.pci_cf8;
> @@ -2618,12 +2617,42 @@ bool_t hvm_send_assist_req_to_ioreq_server(struct hvm_ioreq_server *s,
>      return 0;
>  }
>  
> +static bool_t hvm_complete_assist_req(ioreq_t *p)
> +{
> +    switch (p->type)
> +    {
> +    case IOREQ_TYPE_COPY:
> +    case IOREQ_TYPE_PIO:
> +        if ( p->dir == IOREQ_READ )
> +        {
> +            if ( !p->data_is_ptr )
> +                p->data = ~0ul;
> +            else
> +            {
> +                int i, sign = p->df ? -1 : 1;
> +                uint32_t data = ~0;
> +
> +                for ( i = 0; i < p->count; i++ )
> +                    hvm_copy_to_guest_phys(p->data + sign * i * p->size, &data,
> +                                           p->size);

This is surely bogus for an `ins` which crosses a page boundary?

~Andrew

> +            }
> +        }
> +        /* FALLTHRU */
> +    default:
> +        p->state = STATE_IORESP_READY;
> +        hvm_io_assist(p);
> +        break;
> +    }
> +
> +    return 1;
> +}
> +
>  bool_t hvm_send_assist_req(ioreq_t *p)
>  {
>      struct hvm_ioreq_server *s = hvm_select_ioreq_server(current->domain, p);
>  
>      if ( !s )
> -        return 0;
> +        return hvm_complete_assist_req(p);
>  
>      return hvm_send_assist_req_to_ioreq_server(s, p);
>  }