Re: [PATCH v4 14/17] intel_iommu: Set default aw_bits to 48 in scalable modern mode

[Yi Liu]

On 2024/9/30 17:26, Zhenzhong Duan wrote:

According to VTD spec, stage-1 page table could support 4-level and
5-level paging.

However, 5-level paging translation emulation is unsupported yet.
That means the only supported value for aw_bits is 48.

So default aw_bits to 48 in scalable modern mode. In other cases,
it is still default to 39 for backward compatibility.

Add a check to ensure user specified value is 48 in modern mode
for now.

this is not a simple check. I think your patch makes an auto selection
of aw_bits.

Signed-off-by: Zhenzhong Duan <zhenzhong.d...@intel.com>
Reviewed-by: Clément Mathieu--Drif<clement.mathieu--d...@eviden.com>
---
  include/hw/i386/intel_iommu.h |  2 +-
  hw/i386/intel_iommu.c         | 10 +++++++++-
  2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
index b843d069cc..48134bda11 100644
--- a/include/hw/i386/intel_iommu.h
+++ b/include/hw/i386/intel_iommu.h
@@ -45,7 +45,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(IntelIOMMUState, 
INTEL_IOMMU_DEVICE)
  #define DMAR_REG_SIZE               0x230
  #define VTD_HOST_AW_39BIT           39
  #define VTD_HOST_AW_48BIT           48
-#define VTD_HOST_ADDRESS_WIDTH      VTD_HOST_AW_39BIT
+#define VTD_HOST_AW_AUTO            0xff
  #define VTD_HAW_MASK(aw)            ((1ULL << (aw)) - 1)

#define DMAR_REPORT_F_INTR (1)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 91d7b1abfa..068a08f522 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -3776,7 +3776,7 @@ static Property vtd_properties[] = {
                              ON_OFF_AUTO_AUTO),
      DEFINE_PROP_BOOL("x-buggy-eim", IntelIOMMUState, buggy_eim, false),
      DEFINE_PROP_UINT8("aw-bits", IntelIOMMUState, aw_bits,
-                      VTD_HOST_ADDRESS_WIDTH),
+                      VTD_HOST_AW_AUTO),
      DEFINE_PROP_BOOL("caching-mode", IntelIOMMUState, caching_mode, FALSE),
      DEFINE_PROP_BOOL("x-scalable-mode", IntelIOMMUState, scalable_mode, 
FALSE),
      DEFINE_PROP_BOOL("snoop-control", IntelIOMMUState, snoop_control, false),
@@ -4683,6 +4683,14 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error 
**errp)
          }
      }

+ if (s->aw_bits == VTD_HOST_AW_AUTO) {

+        if (s->scalable_modern) {
+            s->aw_bits = VTD_HOST_AW_48BIT;
+        } else {
+            s->aw_bits = VTD_HOST_AW_39BIT;
+        }
+    }

If the default value of s->aw_bits is still 39, you don't know if it's
set by the admin or the orchestration stack. This is why you need
to change it. right?

+
      if (!s->scalable_modern && s->aw_bits != VTD_HOST_AW_39BIT &&
          s->aw_bits != VTD_HOST_AW_48BIT) {
          error_setg(errp, "%s mode: supported values for aw-bits are: %d, %d",

--
Regards,
Yi Liu