[PATCH 6/6] Introduce per cpu flag (iommu_dont_flush_iotlb) to avoid unnecessary iotlb flush

[Jean Guyader <jean.guyader@eu.citrix.com>]

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Add cpu flag that will be checked by the iommu low level code
to skip iotlb flushes. iommu_iotlb_flush shall be called explicitly.

Signed-off-by: Jean Guyader <jean.guyader@eu.citrix.com>
---
 xen/arch/x86/mm.c                   |   14 ++++++++++++++
 xen/drivers/passthrough/iommu.c     |    5 +++++
 xen/drivers/passthrough/vtd/iommu.c |    6 ++++--
 xen/include/xen/iommu.h             |   12 ++++++++++++
 4 files changed, 35 insertions(+), 2 deletions(-)


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diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 2417fe9..17a8504 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4594,13 +4594,20 @@ static int handle_iomem_range(unsigned long s, unsigned long e, void *p)
 
 static int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap xatp)
 {
+    struct xen_add_to_physmap start_xatp;
     struct page_info *page = NULL;
     unsigned long prev_mfn, mfn = 0, gpfn;
     int rc;
 
     if ( xatp.space != XENMAPSPACE_gmfn_range )
         xatp.size = 1;
+    else
+    {
+        if ( need_iommu(d) )
+            this_cpu(iommu_dont_flush_iotlb) = 1;
+    }
 
+    start_xatp = xatp;
     while ( xatp.size > 0 )
     {
         if ( hypercall_preempt_check() )
@@ -4705,6 +4712,13 @@ static int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap xat
             break;
     }
 
+    if ( xatp.space == XENMAPSPACE_gmfn_range && need_iommu(d) )
+    {
+        this_cpu(iommu_dont_flush_iotlb) = 0;
+        iommu_iotlb_flush(d, start_xatp.idx, start_xatp.size - xatp.size);
+        iommu_iotlb_flush(d, start_xatp.gpfn, start_xatp.size - xatp.size);
+    }
+
     return rc;
 }
 
diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index ca7b37b..bacca11 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -52,6 +52,8 @@ bool_t __read_mostly iommu_hap_pt_share = 1;
 bool_t __read_mostly iommu_debug;
 bool_t __read_mostly amd_iommu_perdev_intremap;
 
+DEFINE_PER_CPU(bool_t, iommu_dont_flush_iotlb);
+
 static void __init parse_iommu_param(char *s)
 {
     char *ss;
@@ -227,6 +229,7 @@ static int iommu_populate_page_table(struct domain *d)
 
     spin_lock(&d->page_alloc_lock);
 
+    this_cpu(iommu_dont_flush_iotlb) = 1;
     page_list_for_each ( page, &d->page_list )
     {
         if ( is_hvm_domain(d) ||
@@ -244,6 +247,8 @@ static int iommu_populate_page_table(struct domain *d)
             }
         }
     }
+    this_cpu(iommu_dont_flush_iotlb) = 0;
+    iommu_iotlb_flush_all(d);
     spin_unlock(&d->page_alloc_lock);
     return 0;
 }
diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 7ec9541..a3dd018 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -660,7 +660,8 @@ static void dma_pte_clear_one(struct domain *domain, u64 addr)
     spin_unlock(&hd->mapping_lock);
     iommu_flush_cache_entry(pte, sizeof(struct dma_pte));
 
-    __intel_iommu_iotlb_flush(domain, addr >> PAGE_SHIFT_4K , 0, 1);
+    if ( !this_cpu(iommu_dont_flush_iotlb) )
+        __intel_iommu_iotlb_flush(domain, addr >> PAGE_SHIFT_4K , 0, 1);
 
     unmap_vtd_domain_page(page);
 
@@ -1753,7 +1754,8 @@ static int intel_iommu_map_page(
     spin_unlock(&hd->mapping_lock);
     unmap_vtd_domain_page(page);
 
-    __intel_iommu_iotlb_flush(d, gfn, dma_pte_present(old), 1);
+    if ( !this_cpu(iommu_dont_flush_iotlb) )
+        __intel_iommu_iotlb_flush(d, gfn, dma_pte_present(old), 1);
 
     return 0;
 }
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index a1034df..6f7fbf7 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -160,4 +160,16 @@ int iommu_do_domctl(struct xen_domctl *, XEN_GUEST_HANDLE(xen_domctl_t));
 void iommu_iotlb_flush(struct domain *d, unsigned long gfn, unsigned int page_count);
 void iommu_iotlb_flush_all(struct domain *d);
 
+/*
+ * The purpose of the iommu_dont_flush_iotlb optional cpu flag is to
+ * avoid unecessary iotlb_flush in the low level IOMMU code.
+ *
+ * iommu_map_page/iommu_unmap_page must flush the iotlb but somethimes
+ * this operation can be really expensive. This flag will be set by the
+ * caller to notify the low level IOMMU code to avoid the iotlb flushes.
+ * iommu_iotlb_flush/iommu_iotlb_flush_all will be explicitly called by
+ * the caller.
+ */
+DECLARE_PER_CPU(bool_t, iommu_dont_flush_iotlb);
+
 #endif /* _IOMMU_H_ */

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