[xen master] IOMMU/EPT: avoid double flushing in shared page table case

[patchbot@xxxxxxx]

commit 83432adeb82122e392a3bfc2a8818d25ca9e69ed
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Oct 23 10:06:53 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Oct 23 10:06:53 2020 +0200

    IOMMU/EPT: avoid double flushing in shared page table case
    
    While the flush coalescing optimization has been helping the non-shared
    case, it has actually lead to double flushes in the shared case (which
    ought to be the more common one nowadays at least): Once from
    *_set_entry() and a second time up the call tree from wherever the
    overriding flag gets played with. In alignment with XSA-346 suppress
    flushing in this case.
    
    Similarly avoid excessive setting of IOMMU_FLUSHF_added on the batched
    flushes: "idx" hasn't been added a new mapping for.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
 xen/arch/x86/mm/p2m-ept.c | 2 +-
 xen/common/memory.c       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 12cf38f6eb..476458b1e0 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -842,7 +842,7 @@ out:
     if ( rc == 0 && p2m_is_hostp2m(p2m) &&
          need_modify_vtd_table )
     {
-        if ( iommu_use_hap_pt(d) )
+        if ( iommu_use_hap_pt(d) && !this_cpu(iommu_dont_flush_iotlb) )
             rc = iommu_iotlb_flush(d, _dfn(gfn), 1ul << order,
                                    (iommu_flags ? IOMMU_FLUSHF_added : 0) |
                                    (vtd_pte_present ? IOMMU_FLUSHF_modified
diff --git a/xen/common/memory.c b/xen/common/memory.c
index 7075e233aa..df85b550a1 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -870,7 +870,7 @@ int xenmem_add_to_physmap(struct domain *d, struct 
xen_add_to_physmap *xatp,
         this_cpu(iommu_dont_flush_iotlb) = 0;
 
         ret = iommu_iotlb_flush(d, _dfn(xatp->idx - done), done,
-                                IOMMU_FLUSHF_added | IOMMU_FLUSHF_modified);
+                                IOMMU_FLUSHF_modified);
         if ( unlikely(ret) && rc >= 0 )
             rc = ret;
 
--
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