[Xen-devel] [PATCH] iommu/quirk: disable shared EPT for Sandybridge and earlier processors.

[<Anshul Makkar anshul.makkar@xxxxxxxxxx>]

From: Anshul Makkar <anshul.makkar@xxxxxxxxxx>

Sandybridge or earlier processors don't have huge page support for
IOTLB which leads to fallback on 4k pages and causes performance issues.

Shared EPT will be disabled only if the user has not provided explicit
choice on the command line.

Signed-off-by: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
---
v2:
   * Removed the use of extra variable to control the shared EPT and made
     the existent variable as tristate.
   * Narrowed down the check for processors to Sandybridge and older including
     Atom processors.

 docs/misc/xen-command-line.markdown  |  2 +-
 xen/drivers/passthrough/iommu.c      |  2 +-
 xen/drivers/passthrough/vtd/quirks.c | 14 ++++++++++++++
 xen/include/xen/iommu.h              |  2 +-
 4 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index a2e427c..6b69ba2 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -896,7 +896,7 @@ debug hypervisor only).
 
 > `sharept`
 
-> Default: `true`
+> Default: `true` if newer than SandyBridge or `false` if Sandybridge or 
earlier.
 
 >> Control whether CPU and IOMMU page tables should be shared.
 
diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index d5137733..9367987 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -51,7 +51,7 @@ bool_t __read_mostly iommu_passthrough;
 bool_t __read_mostly iommu_snoop = 1;
 bool_t __read_mostly iommu_qinval = 1;
 bool_t __read_mostly iommu_intremap = 1;
-bool_t __read_mostly iommu_hap_pt_share = 1;
+s8     __read_mostly iommu_hap_pt_share = -1;
 bool_t __read_mostly iommu_debug;
 bool_t __read_mostly amd_iommu_perdev_intremap = 1;
 
diff --git a/xen/drivers/passthrough/vtd/quirks.c 
b/xen/drivers/passthrough/vtd/quirks.c
index 1888843..7d63c8d 100644
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -320,6 +320,20 @@ void __init platform_quirks_init(void)
     /* Tylersburg interrupt remap quirk */
     if ( iommu_intremap )
         tylersburg_intremap_quirk();
+
+    /*
+     * Disable shared EPT ("sharept") on Sandybridge and older processors
+     * by default.
+     * SandyBridge has no huge page support for IOTLB which leads to fallback
+     * on 4k pages and leads to performance degradation.
+     *
+     * Shared EPT ("sharept") will be disabled only if user has not
+     * provided explicit choice on the command line thus iommu_hap_pt_share is
+     * at its initialized value of -1.
+     */
+    if ( (boot_cpu_data.x86 == 0x06 && (boot_cpu_data.x86_model <= 0x2F ||
+          boot_cpu_data.x86_model == 0x36)) && (iommu_hap_pt_share == -1) )
+        iommu_hap_pt_share = 0;
 }
 
 /*
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 8f3a20e..d52d06f 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -31,7 +31,7 @@ extern bool_t iommu_enable, iommu_enabled;
 extern bool_t force_iommu, iommu_verbose;
 extern bool_t iommu_workaround_bios_bug, iommu_igfx, iommu_passthrough;
 extern bool_t iommu_snoop, iommu_qinval, iommu_intremap;
-extern bool_t iommu_hap_pt_share;
+extern s8 iommu_hap_pt_share;
 extern bool_t iommu_debug;
 extern bool_t amd_iommu_perdev_intremap;
 
-- 
1.9.1


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