[PATCH v2 11/11] OvmfPkg/PlatformPei: detect SMRAM at default SMBASE (for real)

["Laszlo Ersek" <lersek@redhat.com>]

Now that the SMRAM at the default SMBASE is honored everywhere necessary,
implement the actual detection. The (simple) steps are described in
previous patch "OvmfPkg/IndustryStandard: add MCH_DEFAULT_SMBASE* register
macros".

Regarding CSM_ENABLE builds: according to the discussion with Jiewen at

  https://edk2.groups.io/g/devel/message/48082
  http://mid.mail-archive.com/74D8A39837DF1E4DA445A8C0B3885C503F7C9D2F@shsmsx102.ccr.corp.intel.com

if the platform has SMRAM at the default SMBASE, then we have to

(a) either punch a hole in the legacy E820 map as well, in
    LegacyBiosBuildE820() [OvmfPkg/Csm/LegacyBiosDxe/LegacyBootSupport.c],

(b) or document, or programmatically catch, the incompatibility between
    the "SMRAM at default SMBASE" and "CSM" features.

Because CSM is out of scope for the larger "VCPU hotplug with SMM"
feature, option (b) applies. Therefore, if the CSM is enabled in the OVMF
build, then PlatformPei will not attempt to detect SMRAM at the default
SMBASE, at all. This is approach (4) -- the most flexible one, for
end-users -- from:

  http://mid.mail-archive.com/868dcff2-ecaa-e1c6-f018-abe7087d640c@redhat.com
  https://edk2.groups.io/g/devel/message/48348

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1512
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---

Notes:
    v2:
    - In CSM_ENABLE builds, pretend that SMRAM never exists at the default
      SMBASE [Jiewen]
    - trim Cc list

 OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
 OvmfPkg/PlatformPei/MemDetect.c     | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index 25229618ed13..c51a6176aa2e 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -106,6 +106,7 @@ [FixedPcd]
   gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
 
 [FeaturePcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdCsmEnable
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
 
 [Ppis]
diff --git a/OvmfPkg/PlatformPei/MemDetect.c b/OvmfPkg/PlatformPei/MemDetect.c
index 8fdc9c2ed7c9..47dc9c543719 100644
--- a/OvmfPkg/PlatformPei/MemDetect.c
+++ b/OvmfPkg/PlatformPei/MemDetect.c
@@ -103,6 +103,22 @@ Q35SmramAtDefaultSmbaseInitialization (
   ASSERT (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID);
 
   mQ35SmramAtDefaultSmbase = FALSE;
+  if (FeaturePcdGet (PcdCsmEnable)) {
+    DEBUG ((DEBUG_INFO, "%a: SMRAM at default SMBASE not checked due to CSM\n",
+      __FUNCTION__));
+  } else {
+    UINTN CtlReg;
+    UINT8 CtlRegVal;
+
+    CtlReg = DRAMC_REGISTER_Q35 (MCH_DEFAULT_SMBASE_CTL);
+    PciWrite8 (CtlReg, MCH_DEFAULT_SMBASE_QUERY);
+    CtlRegVal = PciRead8 (CtlReg);
+    mQ35SmramAtDefaultSmbase = (BOOLEAN)(CtlRegVal ==
+                                         MCH_DEFAULT_SMBASE_IN_RAM);
+    DEBUG ((DEBUG_INFO, "%a: SMRAM at default SMBASE %a\n", __FUNCTION__,
+      mQ35SmramAtDefaultSmbase ? "found" : "not found"));
+  }
+
   PcdStatus = PcdSetBoolS (PcdQ35SmramAtDefaultSmbase,
                 mQ35SmramAtDefaultSmbase);
   ASSERT_RETURN_ERROR (PcdStatus);
-- 
2.19.1.3.g30247aa5d201