[Xen-devel] [PATCH] Avoid needless flush cache when guest change MTRR

[Liang Li <liang.z.li@xxxxxxxxx>]

Flushing cache is needed only when guest has IOMMU device, using
need_iommu(d) can minimize the impact to guest with device assigned,
since a guest may be hot plugged with a device thus there may be dirty
cache lines before need_iommu(d) becoming true, force the flush_all
when the first device is assigned to guest to amend this issue.

Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
---
 xen/arch/x86/hvm/mtrr.c       | 2 +-
 xen/drivers/passthrough/pci.c | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/mtrr.c b/xen/arch/x86/hvm/mtrr.c
index ee18553..858fb7e 100644
--- a/xen/arch/x86/hvm/mtrr.c
+++ b/xen/arch/x86/hvm/mtrr.c
@@ -791,7 +791,7 @@ HVM_REGISTER_SAVE_RESTORE(MTRR, hvm_save_mtrr_msr, 
hvm_load_mtrr_msr,
 
 void memory_type_changed(struct domain *d)
 {
-    if ( iommu_enabled && d->vcpu && d->vcpu[0] )
+    if ( need_iommu(d) && d->vcpu && d->vcpu[0] )
     {
         p2m_memory_type_changed(d);
         flush_all(FLUSH_CACHE);
diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 78c6977..a023d1d 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -1365,6 +1365,11 @@ static int assign_device(struct domain *d, u16 seg, u8 
bus, u8 devfn)
             }
         }
         d->need_iommu = 1;
+        /* There may be dirty cache lines when a device is assigned
+         * and before need_iommu(d) becoming true, this will cause
+         * memory_type_changed lose effect if memory type changes.
+         * Call memory_type_changed here to amend this. */
+        memory_type_changed(d);
     }
 
     pdev = pci_get_pdev_by_domain(hardware_domain, seg, bus, devfn);
-- 
1.9.1


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel