[PATCH edk2 hci-8.1] OvmfPkg/PlatformInitLib: switch to 5-level paging only above 16TB #VSTOR-152672 #VSTOR-152405

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

With PcdUse5LevelPageTable the 64-bit PEI decides per guest whether to
hand the OS over in 4- or 5-level paging mode.  Without a fw_cfg
override it uses 5-level paging as soon as the guest address space
(RAM plus the memory hotplug window) reaches 1TB.

That threshold is too low for us:

  * 4-level firmware paging already covers 64TB of address space, so
    5-level paging below that buys nothing and only changes what the OS
    sees at ExitBootServices;
  * on Windows that means booting the LA57 kernel (ntkrla57.exe), which
    bugchecks on AMD guests exposed to the ARCH_CAPABILITIES MSR
    (VSTOR-152405) and breaks Windows Setup.  QEMU since the commit
    7fc0e1c9f577 ("i386: hide la57 at fresh start on vz machine types
    that show ARCH_CAPABILITIES #VSTOR-152405") now hides la57 on the
    VZ machine types that expose the MSR, but the firmware shouldn't
    depend on that.

Raise the threshold to 16TB.  Ordinary guests, including those with a
large hotplug window, stay in 4-level paging.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 OvmfPkg/Library/PlatformInitLib/MemDetect.c | 6 +++---
 OvmfPkg/RUNTIME_CONFIG.md                   | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/OvmfPkg/Library/PlatformInitLib/MemDetect.c b/OvmfPkg/Library/PlatformInitLib/MemDetect.c
index 937e2b77a5..7220db8ef9 100644
--- a/OvmfPkg/Library/PlatformInitLib/MemDetect.c
+++ b/OvmfPkg/Library/PlatformInitLib/MemDetect.c
@@ -967,7 +967,7 @@ Switch4Level (
    Should that not be the case the function checks the size of the address space
    needed, which is the RAM installed plus fw_cfg reservations.  The downgrade
    to 4-level paging will happen for small guests where the address space needed
-   is lower than 1TB.
+   is lower than 16TB.
 
 
    This function will also log the paging level used and the reason for that.
@@ -1002,9 +1002,9 @@ PlatformSetupPagingLevel (
              );
   switch (Status) {
     case EFI_NOT_FOUND:
-      if (PlatformInfoHob->FirstNonAddress < (1ll << 40)) {
+      if (PlatformInfoHob->FirstNonAddress < (1ll << 44)) {
         //
-        // If the highest address actually used is below 1TB switch back into
+        // If the highest address actually used is below 16TB switch back into
         // 4-level paging mode for better compatibility with older guests.
         //
         DEBUG ((DEBUG_INFO, "%a: using 4-level paging (default for small guest)\n", __func__));
diff --git a/OvmfPkg/RUNTIME_CONFIG.md b/OvmfPkg/RUNTIME_CONFIG.md
index b75a5dacad..3bef1e6e4a 100644
--- a/OvmfPkg/RUNTIME_CONFIG.md
+++ b/OvmfPkg/RUNTIME_CONFIG.md
@@ -228,7 +228,7 @@ paging levels are better for compatibility, not all OSes can handle
 levels are better for huge VMs, the address space managed by OVMF can
 be larger.
 
-Default: Use 5-level paging in case more than 1TB of memory is
+Default: Use 5-level paging in case more than 16TB of memory is
 present, 4-level paging otherwise.
 
 Usage:
-- 
2.47.1