Hi Jan,
On 6/4/19 5:14 PM, Jan Beulich wrote:
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)?
And I answered that mfn_to_gmfn() is used in the function. I really
don't want to implement the macro on Arm (even if it is dummy).
You haven't answered back to that comment and I assumed this was fine
with you...
- 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.
ok.
--- 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.
ok.
Cheers,
--
Julien Grall
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