[PATCH 3/3] x86/vtd: Switch model check to VFM

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

This form is shorer and more legible.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>

As this is the first transformation, an anlysis of the code generation change:

before:
<quirk_iommu_caps>:
               8b 05 4a 7e 09 00        mov    0x97e4a(%rip),%eax        # 
<boot_cpu_data>
               25 00 ff ff 00           and    $0xffff00,%eax
               3d 00 06 01 00           cmp    $0x10600,%eax
           /-- 74 0e                    je     <quirk_iommu_caps+0x20>
        /--|-> e9 59 8a dc ff           jmp    <__x86_return_thunk>
        |  |   66 0f 1f 84 00 00 00     nopw   0x0(%rax,%rax,1)
        |  |   00 00
        |  \-> 0f b6 05 29 7e 09 00     movzbl 0x97e29(%rip),%eax        # 
<boot_cpu_data>
        |      3c 2a                    cmp    $0x2a,%al
        |  /-- 74 04                    je     <quirk_iommu_caps+0x2f>
        |  |   3c 2d                    cmp    $0x2d,%al
        \--|-- 75 e3                    jne    <quirk_iommu_caps+0x12>
           \-> 48 b8 ff ff ff ff c3     movabs $0xffffffc3ffffffff,%rax
               ff ff ff
               48 21 47 20              and    %rax,0x20(%rdi)
               e9 2e 8a dc ff           jmp    <__x86_return_thunk>

after:
<quirk_iommu_caps>:
            8b 05 4a 7e 09 00           mov    0x97e4a(%rip),%eax        # 
<boot_cpu_data>
            3d 2a 06 01 00              cmp    $0x1062a,%eax
        /-- 74 13                       je     <quirk_iommu_caps+0x20>
        |   3d 2d 06 01 00              cmp    $0x1062d,%eax
        +-- 74 0c                       je     <quirk_iommu_caps+0x20>
        |   e9 57 8a dc ff              jmp    <__x86_return_thunk>
        |   0f 1f 80 00 00 00 00        nopl   0x0(%rax)
        \-> 48 b8 ff ff ff ff c3        movabs $0xffffffc3ffffffff,%rax
            ff ff ff
            48 21 47 20                 and    %rax,0x20(%rdi)
            e9 3d 8a dc ff              jmp    <__x86_return_thunk>

Previously, GCC managed to merge the "x86_vendor == X86_VENDOR_INTEL && x86 ==
6" condition, but performed a second load for x86_model.

Afterwards, there's a single load, and two compares.

Neither managed to merge the model checks together by playing with bit 2, but
that's something that compilers could learn to and is not suitable to express
at the C level for this kind of logic.

Unrelated to this change, it would be rather better to do `andl $0xc3,
0x24(%rdi)` than to manifest a 64bit constant.
---
 xen/arch/x86/include/asm/cpufeature.h | 2 +-
 xen/drivers/passthrough/vtd/quirks.c  | 7 +++----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/include/asm/cpufeature.h 
b/xen/arch/x86/include/asm/cpufeature.h
index ba2c1c1c7416..f8b85c0f9520 100644
--- a/xen/arch/x86/include/asm/cpufeature.h
+++ b/xen/arch/x86/include/asm/cpufeature.h
@@ -28,7 +28,7 @@
 
 #define VFM_MAKE(v, f, m) (MASK_INSR(v, VFM_VENDOR_MASK) | \
                            MASK_INSR(f, VFM_FAMILY_MASK) | \
-                           MASK_INSR(f, VFM_MODEL_MASK))
+                           MASK_INSR(m, VFM_MODEL_MASK))
 
 #define VFM_MODEL(vfm)  MASK_EXTR(vfm, VFM_MODEL_MASK)
 #define VFM_FAMILY(vfm) MASK_EXTR(vfm, VFM_FAMILY_MASK)
diff --git a/xen/drivers/passthrough/vtd/quirks.c 
b/xen/drivers/passthrough/vtd/quirks.c
index dc3dac749ce6..0a10a46d90f7 100644
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -30,6 +30,7 @@
 #include <xen/pci_regs.h>
 #include <xen/keyhandler.h>
 #include <asm/msi.h>
+#include <asm/intel-family.h>
 #include <asm/irq.h>
 #include <asm/pci.h>
 
@@ -630,9 +631,7 @@ void __init quirk_iommu_caps(struct vtd_iommu *iommu)
      * model because the client parts don't expose their IOMMUs as PCI devices
      * we could match with a Device ID.
      */
-    if ( boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
-         boot_cpu_data.x86 == 6 &&
-         (boot_cpu_data.x86_model == 0x2a ||
-          boot_cpu_data.x86_model == 0x2d) )
+    if ( boot_cpu_data.vfm == INTEL_SANDYBRIDGE ||
+         boot_cpu_data.vfm == INTEL_SANDYBRIDGE_X )
         iommu->cap &= ~(0xful << 34);
 }
-- 
2.39.5