Re: [Xen-devel] [PATCH v9 04/17] vt-d: VT-d Posted-Interrupts feature detection

[Tian, Kevin]

> From: Wu, Feng
> Sent: Tuesday, November 03, 2015 4:43 PM
> 
> 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 
> CC: Kevin Tian 
> Signed-off-by: Feng Wu 
> Reviewed-by: Konrad Rzeszutek Wilk 
> Reviewed-by: Jan Beulich 

Acked-by: Kevin Tian 

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[Xen-devel] [PATCH v9 04/17] vt-d: VT-d Posted-Interrupts feature detection

[Feng Wu]

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 
CC: Kevin Tian 
Signed-off-by: Feng Wu 
Reviewed-by: Konrad Rzeszutek Wilk 
Reviewed-by: Jan Beulich 
---
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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