[Xen-devel] [PATCH v8 04/17] vt-d: VT-d Posted-Interrupts feature detection

[Feng Wu <feng.wu@xxxxxxxxx>]

VT-d Posted-Interrupts is an enhancement to CPU side Posted-Interrupt.
With VT-d Posted-Interrupts enabled, external interrupts from
direct-assigned devices can be delivered to guests without VMM
intervention when guest is running in non-root mode.

CC: Yang Zhang <yang.z.zhang@xxxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v7:
- Remove pointless "if non iommu_intremap then disable iommu_intpost" logic
- Don't need to check !iommu_intremap or !iommu_intpost when setting 
iommu_intpost to 0

v5:
- Remove blank line

v4:
- Correct a logic error when setting iommu_intpost to 0

v3:
- Remove the "if no intremap then no intpost" logic in
  intel_vtd_setup(), it is covered in the iommu_setup().
- Add "if no intremap then no intpost" logic in the end
  of init_vtd_hw() which is called by vtd_resume().

So the logic exists in the following three places:
- parse_iommu_param()
- iommu_setup()
- init_vtd_hw()

 xen/drivers/passthrough/vtd/iommu.c | 14 ++++++++++++--
 xen/drivers/passthrough/vtd/iommu.h |  1 +
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index 1dffc40..8dee731 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -2147,8 +2147,8 @@ int __init intel_vtd_setup(void)
     }
 
     /* We enable the following features only if they are supported by all VT-d
-     * engines: Snoop Control, DMA passthrough, Queued Invalidation and
-     * Interrupt Remapping.
+     * engines: Snoop Control, DMA passthrough, Queued Invalidation, Interrupt
+     * Remapping, and Posted Interrupt
      */
     for_each_drhd_unit ( drhd )
     {
@@ -2176,6 +2176,14 @@ int __init intel_vtd_setup(void)
         if ( iommu_intremap && !ecap_intr_remap(iommu->ecap) )
             iommu_intremap = 0;
 
+        /*
+         * We cannot use posted interrupt if X86_FEATURE_CX16 is
+         * not supported, since we count on this feature to
+         * atomically update 16-byte IRTE in posted format.
+         */
+        if ( !cap_intr_post(iommu->cap) || !cpu_has_cx16 )
+            iommu_intpost = 0;
+
         if ( !vtd_ept_page_compatible(iommu) )
             iommu_hap_pt_share = 0;
 
@@ -2201,6 +2209,7 @@ int __init intel_vtd_setup(void)
     P(iommu_passthrough, "Dom0 DMA Passthrough");
     P(iommu_qinval, "Queued Invalidation");
     P(iommu_intremap, "Interrupt Remapping");
+    P(iommu_intpost, "Posted Interrupt");
     P(iommu_hap_pt_share, "Shared EPT tables");
 #undef P
 
@@ -2220,6 +2229,7 @@ int __init intel_vtd_setup(void)
     iommu_passthrough = 0;
     iommu_qinval = 0;
     iommu_intremap = 0;
+    iommu_intpost = 0;
     return ret;
 }
 
diff --git a/xen/drivers/passthrough/vtd/iommu.h 
b/xen/drivers/passthrough/vtd/iommu.h
index ac71ed1..22abefe 100644
--- a/xen/drivers/passthrough/vtd/iommu.h
+++ b/xen/drivers/passthrough/vtd/iommu.h
@@ -61,6 +61,7 @@
 /*
  * Decoding Capability Register
  */
+#define cap_intr_post(c)       (((c) >> 59) & 1)
 #define cap_read_drain(c)      (((c) >> 55) & 1)
 #define cap_write_drain(c)     (((c) >> 54) & 1)
 #define cap_max_amask_val(c)   (((c) >> 48) & 0x3f)
-- 
2.1.0


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