Re: [Xen-devel] [PATCH] iommu/quirk: disable shared EPT for Sandybridge and earlier processors.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.11.15 at 18:17, <Anshul Makkar anshul.makkar@xxxxxxxxxx> wrote:
> --- a/xen/drivers/passthrough/vtd/quirks.c
> +++ b/xen/drivers/passthrough/vtd/quirks.c
> @@ -320,6 +320,20 @@ void __init platform_quirks_init(void)
>      /* Tylersburg interrupt remap quirk */
>      if ( iommu_intremap )
>          tylersburg_intremap_quirk();
> +
> +    /*
> +     * Disable shared EPT ("sharept") on Sandybridge and older processors
> +     * by default.
> +     * SandyBridge has no huge page support for IOTLB which leads to fallback
> +     * on 4k pages and leads to performance degradation.
> +     *
> +     * Shared EPT ("sharept") will be disabled only if user has not
> +     * provided explicit choice on the command line thus iommu_hap_pt_share 
> is
> +     * at its initialized value of -1.
> +     */
> +    if ( (boot_cpu_data.x86 == 0x06 && (boot_cpu_data.x86_model <= 0x2F ||
> +          boot_cpu_data.x86_model == 0x36)) && (iommu_hap_pt_share == -1) )
> +        iommu_hap_pt_share = 0;

If we really want to do this, then I think we should key this on
EPT but not VT-d having 2M support, instead of on CPU models.

Also - with the above only marginally relevant - the line split and/or
indentation is wrong.

Jan


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