Re: [PATCH 2/2] intel_iommu: Only allow interrupt remapping to be enabled if it's supported

[Jason Wang <jasowang@redhat.com>]

On Thu, Dec 2, 2021 at 4:58 AM David Woodhouse <dwmw2@infradead.org> wrote:
>
> From: David Woodhouse <dwmw@amazon.co.uk>
>
> We should probably check if we were meant to be exposing IR, before
> letting the guest turn the IRE bit on.

This looks correct, but it's a change of guest noticeable behaviour.
It's probably fine since we don't expect a guest that enable IR
without checking ecap.

So

Acked-by: Jason Wang <jasowang@redhat.com>

>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>  hw/i386/intel_iommu.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index ffc852d110..297e1972f8 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -2197,6 +2197,7 @@ static void vtd_handle_gcmd_ire(IntelIOMMUState *s, bool en)
>  /* Handle write to Global Command Register */
>  static void vtd_handle_gcmd_write(IntelIOMMUState *s)
>  {
> +    X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(s);
>      uint32_t status = vtd_get_long_raw(s, DMAR_GSTS_REG);
>      uint32_t val = vtd_get_long_raw(s, DMAR_GCMD_REG);
>      uint32_t changed = status ^ val;
> @@ -2218,7 +2219,8 @@ static void vtd_handle_gcmd_write(IntelIOMMUState *s)
>          /* Set/update the interrupt remapping root-table pointer */
>          vtd_handle_gcmd_sirtp(s);
>      }
> -    if (changed & VTD_GCMD_IRE) {
> +    if ((changed & VTD_GCMD_IRE) &&
> +        x86_iommu_ir_supported(x86_iommu)) {
>          /* Interrupt remap enable/disable */
>          vtd_handle_gcmd_ire(s, val & VTD_GCMD_IRE);
>      }
> --
> 2.31.1
>
>