Hi,
On 1/28/19 3:34 PM, Andrii Anisov wrote:
From: Andrii Anisov <andrii_ani...@epam.com>
In case if the p2m table is shared to IOMMU, invalidating it turns IOMMU to
translation faults that could be not repaired.
Fixed patch check for the corresponded condition and has a comment for one
introduced p2m_invalidate_root() call, but miss them for another. So put the
`if` and the comment in place.
This was missed on purpose. Let me explain why. The call to
p2m_invalidate_root() arch_domain_creation_finished is called by *all*
the domain at boot to try to optimize the set/way case.
The check iommu_use_hap_pt in that context is to prevent guest not using
Set/Way to become unusable under the IOMMU use-case.
In your case, you seem to have a guest OS using set/way and yet sharing
the P2M with the IOMMU. You have the choice between:
1) Crashing on IOMMU fault
2) Become very slow and potentially unusable because you now have to go
through the full P2M every time you do a Set/Way.
1) was my favored option because Set/Way should really not be used by
the guest. It was implemented by courtesy to the guest OS and I would
not rely on everything working.
Can you explain what is your use-case (OS used, IOMMU, platform...)?
Cheers,
Fixes: 2148a12 ("xen/arm: Track page accessed between batch of Set/Way
operations")
Signed-off-by: Andrii Anisov <andrii_ani...@epam.com>
---
xen/arch/arm/p2m.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 059a391..2367e09 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1708,8 +1708,13 @@ void p2m_flush_vm(struct vcpu *v)
/*
* Invalidate the p2m to track which page was modified by the guest
* between call of p2m_flush_vm().
+ *
+ * This is only turned when IOMMU is not used or the page-table are
+ * not shared because bit[0] (e.g valid bit) unset will result
+ * IOMMU fault that could be not fixed-up.
*/
- p2m_invalidate_root(p2m);
+ if ( !iommu_use_hap_pt(v->domain) )
+ p2m_invalidate_root(p2m);
v->arch.need_flush_to_ram = false;
}
--
Julien Grall
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