From: yeeli <seven.yi.lee@gmail.com>

If VT-D hardware supports scalable mode, Linux will set the IQA DW field
(bit11). In qemu, the vtd_mem_write and vtd_update_iq_dw set DW field well.
However, vtd_mem_read the DW field wrong because "& VTD_IQA_QS" dropped the
value of DW.
Replace "&VTD_IQA_QS" with "& (VTD_IQA_QS | VTD_IQA_DW_MASK)" could save
the DW field.

Test patch as below:

config the "x-scalable-mode" option:
"-device intel-iommu,caching-mode=on,x-scalable-mode=on,aw-bits=48"

After Linux OS boot, check the IQA_REG DW Field by usage 1 or 2:

1. IOMMU_DEBUGFS:
Before fix:
cat /sys/kernel/debug/iommu/intel/iommu_regset |grep IQA
IQA             	0x90		0x00000001001da001

After fix:
cat /sys/kernel/debug/iommu/intel/iommu_regset |grep IQA
IQA             	0x90		0x00000001001da801

Check DW field(bit11) is 1.

2. devmem2 read the IQA_REG (offset 0x90):
Before fix:
devmem2 0xfed90090
/dev/mem opened.
Memory mapped at address 0x7f72c795b000.
Value at address 0xFED90090 (0x7f72c795b090): 0x1DA001

After fix:
devmem2 0xfed90090
/dev/mem opened.
Memory mapped at address 0x7fc95281c000.
Value at address 0xFED90090 (0x7fc95281c090): 0x1DA801

Check DW field(bit11) is 1.

Signed-off-by: yeeli <seven.yi.lee@gmail.com>
Message-Id: <20240725031858.1529902-1-seven.yi.lee@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/i386/intel_iommu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 9a768f0b44..16d2885fcc 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -2947,7 +2947,9 @@ static uint64_t vtd_mem_read(void *opaque, hwaddr addr, unsigned size)
 
     /* Invalidation Queue Address Register, 64-bit */
     case DMAR_IQA_REG:
-        val = s->iq | (vtd_get_quad(s, DMAR_IQA_REG) & VTD_IQA_QS);
+        val = s->iq |
+              (vtd_get_quad(s, DMAR_IQA_REG) &
+              (VTD_IQA_QS | VTD_IQA_DW_MASK));
         if (size == 4) {
             val = val & ((1ULL << 32) - 1);
         }
-- 
MST