>>> On 03.06.19 at 18:03, <julien.gr...@arm.com> wrote:
> While Arm never had a M2P, the implementation of mfn_to_gmfn is pretty
> bogus as we directly return the MFN passed in parameter.
>
> Thankfully, the use of mfn_to_gmfn is pretty limited on Arm today. There
> are only 3 callers:
> - iommu_hwdom_init: mfn_to_gmfn is used for creating IOMMU
> page-tables when the P2M is not shared with the IOMMU. No issues so
> far as Arm does not yet support non-shared P2M case.
> - memory_exchange: Arm cannot not use it because steal_page is not
> implemented.
> - getdomaininfo: Toolstack may map the shared page. It looks like
> this is mostly used for mapping the P2M of PV guest. Therefore the
> issue might be minor.
>
> Implementing the M2P on Arm is not planned. The M2P would require
> significant
> amount of VA address (very tough on 32-bit) that can hardly be justified with
> the current use of mfn_to_gmfn.
> - iommu_hwdom_init: mfn_to_gmfn is used because the creating of the
> IOMMU page-tables is delayed until the first device is assigned.
> In the embedded case, we will known in most of the times what
> devices are assigned during the domain creation. So it is possible
> to take to enable the IOMMU from start. See [1] for the patch.
> - memory_exchange: This does not work and I haven't seen any
> request for it so far.
> - getdomaininfo: The structure on Arm does not seem to contain a lot
> of useful information on Arm. It is unclear whether we want to
> allow the toolstack mapping it on Arm.
>
> This patch introduces a config option HAS_M2P to tell whether an
> architecture implements the M2P.
> - iommu_hwdom_init: For now, we require the M2P support when the IOMMU
> is not sharing the P2M.
> - memory_exchange: The hypercall is marked as not supported when the
> M2P does not exist.
But where's the connection between there being M2P and the
availability of this operation? I think I've suggested so before:
Why don't we simply disable this operation for translated
guests (in an independent patch)?
> - getdomaininfo: A new helper is introduced to wrap the call to
> mfn_to_gfn/mfn_to_gmfn. For Arm, a fixed value will be provided that will
> fail on mapping if used.
This reads slightly stale now.
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -188,9 +188,10 @@ void __hwdom_init iommu_hwdom_init(struct domain *d)
> hd->need_sync = iommu_hwdom_strict && !iommu_use_hap_pt(d);
> if ( need_iommu_pt_sync(d) )
> {
> + int rc = 0;
> +#ifdef CONFIG_HAS_M2P
> struct page_info *page;
> unsigned int i = 0, flush_flags = 0;
> - int rc = 0;
>
> page_list_for_each ( page, &d->page_list )
> {
> @@ -221,6 +222,11 @@ void __hwdom_init iommu_hwdom_init(struct domain *d)
> if ( rc )
> printk(XENLOG_WARNING "d%d: IOMMU mapping failed: %d\n",
> d->domain_id, rc);
> +#else
> + ASSERT_UNREACHABLE();
> + rc = -EOPNOTSUPP;
> +#endif
> +
> }
Please don't add a blank line ahead of a closing brace.
Jan
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