Re: [Xen-devel] [PATCH v2] 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 15:57
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Jan Beulich
> <JBeulich@xxxxxxxx>; Roger Pau Monne <roger.pau@xxxxxxxxxx>; Wei Liu
> <wei.liu2@xxxxxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>
> Subject: [PATCH v2] 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 either already switched to or has
> always been in disabled state, and the shared PT test would always be
> false.
> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>

Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> ---
> v2: fix bug and update comment.
> ---
>  xen/drivers/passthrough/vtd/iommu.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/drivers/passthrough/vtd/iommu.c
> b/xen/drivers/passthrough/vtd/iommu.c
> index f94b522c73..4d1ff10817 100644
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -1752,7 +1752,17 @@ static void iommu_domain_teardown(struct domain *d)
>          xfree(mrmrr);
>      }
> 
> -    if ( iommu_use_hap_pt(d) )
> +    ASSERT(iommu_enabled);
> +
> +    /*
> +     * We can't use iommu_use_hap_pt here because either IOMMU state
> +     * is already changed to IOMMU_STATUS_disabled at this point or
> +     * has always been IOMMU_STATUS_disabled.
> +     *
> +     * We also need to test if HAP is enabled because PV guests can
> +     * enter this path too.
> +     */
> +    if ( hap_enabled(d) && iommu_hap_pt_share )
>          return;
> 
>      spin_lock(&hd->arch.mapping_lock);
> --
> 2.11.0


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