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Re: [XEN PATCH 1/3] VT-d: Disable IOMMU if cx16 isn't supported


  • To: Teddy Astie <teddy.astie@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 21 Mar 2024 11:51:38 +0100
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  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Thu, 21 Mar 2024 10:51:49 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 21.03.2024 11:28, Teddy Astie wrote:
> No hardware has VT-d support while not having cx16 support, consider 
> disabling IOMMU in this case to avoid potentially buggy code.

Like in patch 2 (which for whatever reason made it through quite a bit earlier),
why "consider"? Your change does disable the IOMMU in that case, you don't 
merely
consider doing so.

> @@ -394,8 +373,7 @@ static int ioapic_rte_to_remap_entry(struct vtd_iommu 
> *iommu,
>      remap_rte->reserved = 0;
>      /* Indicate remap format. */
>      remap_rte->format = 1;
> -
> -    /* If cmpxchg16b is not available the caller must mask the IO-APIC pin. 
> */
> +    

Please don't introduce lines with trailing blanks.

> @@ -2630,6 +2598,15 @@ static int __init cf_check vtd_setup(void)
>      int ret;
>      bool reg_inval_supported = true;
>  
> +    if ( unlikely(!cpu_has_cx16) )
> +    {
> +        printk(XENLOG_ERR VTDPREFIX
> +               "IOMMU: CPU doesn't support CMPXCHG16B, disabling\n");
> +
> +        ret = -ENOSYS;
> +        goto error;
> +    }

One thing I forgot to mention when replying to patch 2, applying here
equally: vtd_setup() isn't necessarily the first bit of IOMMU setup done.
For x2APIC enabling earlier calls out of x2apic_bsp_setup() exist, which
also need taking care of.

Jan



 


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