Re: [Xen-devel] [PATCH] x86/vtd: fix IOMMU share PT destruction path

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx]
> Sent: 09 October 2018 11:42
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Jan Beulich <JBeulich@xxxxxxxx>; Roger Pau Monne
> <roger.pau@xxxxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>
> Subject: [PATCH] x86/vtd: fix IOMMU share PT destruction path
> 
> Commit 2916951c1 ("mm / iommu: include need_iommu() test in
> iommu_use_hap_pt()") included need_iommu() in iommu_use_hap_pt and
> 91d4eca7add (" mm / iommu: split need_iommu() into has_iommu_pt() and
> need_iommu_pt_sync()") made things finer grain by spliting need_iommu
> into three states.
> 
> The destruction path can't use iommu_use_hap_pt because at the point
> platform op is called, IOMMU is already switched to disabled state and
> the shared PT test would always be false.
> 

This is VT-d specific and the issue could affect AMD too. Can't you just switch 
round the call to teardown and setting IOMMU_status_disabled in 
xen/drivers/passthrough/iommu.c:iommu_teardown()?

  Paul


> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  xen/drivers/passthrough/vtd/iommu.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/drivers/passthrough/vtd/iommu.c
> b/xen/drivers/passthrough/vtd/iommu.c
> index f94b522c73..d66d9e8ad0 100644
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -1752,7 +1752,13 @@ static void iommu_domain_teardown(struct domain *d)
>          xfree(mrmrr);
>      }
> 
> -    if ( iommu_use_hap_pt(d) )
> +    ASSERT(hap_enabled(d));
> +
> +    /*
> +     * We can't use iommu_use_hap_pt here because the IOMMU state is
> already
> +     * changed to IOMMU_STATUS_disabled at this point.
> +     */
> +    if ( iommu_hap_pt_share )
>          return;
> 
>      spin_lock(&hd->arch.mapping_lock);
> --
> 2.11.0


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