Re: [Xen-devel] [PATCH v3 01/10] ioreq: terminate cf8 handling at hypervisor level

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Roger 
> Pau Monne
> Sent: 30 September 2019 14:32
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Paul Durrant <paul@xxxxxxx>; 
> Wei Liu <wl@xxxxxxx>; Jan
> Beulich <jbeulich@xxxxxxxx>; Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Subject: [Xen-devel] [PATCH v3 01/10] ioreq: terminate cf8 handling at 
> hypervisor level
> 
> Do not forward accesses to cf8 to external emulators, decoding of PCI
> accesses is handled by Xen, and emulators can request handling of
> config space accesses of devices using the provided ioreq interface.
> 
> Fully terminate cf8 accesses at the hypervisor level, by improving the
> existing hvm_access_cf8 helper to also handle register reads, and
> always return X86EMUL_OKAY in order to terminate the emulation.
> 
> Note that without this change in the absence of some external emulator
> that catches accesses to cf8 read requests to the register would
> misbehave, as the ioreq internal handler did not handle those.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Paul Durrant <paul@xxxxxxx>

> ---
> Changes since v2:
>  - Allow ioreq servers to map 0xcf8 and 0xcfc, even if those are
>    handled by the hypervisor.
> 
> Changes since v1:
>  - New in this version.
> ---
>  xen/arch/x86/hvm/ioreq.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/ioreq.c b/xen/arch/x86/hvm/ioreq.c
> index d347144096..5e503ce498 100644
> --- a/xen/arch/x86/hvm/ioreq.c
> +++ b/xen/arch/x86/hvm/ioreq.c
> @@ -1518,11 +1518,15 @@ static int hvm_access_cf8(
>  {
>      struct domain *d = current->domain;
> 
> -    if ( dir == IOREQ_WRITE && bytes == 4 )
> +    if ( bytes != 4 )
> +        return X86EMUL_OKAY;
> +
> +    if ( dir == IOREQ_WRITE )
>          d->arch.hvm.pci_cf8 = *val;
> +    else
> +        *val = d->arch.hvm.pci_cf8;
> 
> -    /* We always need to fall through to the catch all emulator */
> -    return X86EMUL_UNHANDLEABLE;
> +    return X86EMUL_OKAY;
>  }
> 
>  void hvm_ioreq_init(struct domain *d)
> --
> 2.23.0
> 
> 
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