[PATCH] OvmfPkg/Sec: Clear the Cache Disable flag in the CR0 register

[Jordan Justen <jordan.l.justen@intel.com>]

Clear the CD (Cache Disable) flag in the CR0 register. When the VM
implements the CD flag, this can substantially decrease the time it
takes to decompress the firmware volumes.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Tested-by: Peter Fang <peter.fang@intel.com>
Cc: Peter Fang <peter.fang@intel.com>
Cc: Maurice Ma <maurice.ma@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Julien Grall <julien.grall@linaro.org>
---
 OvmfPkg/Sec/Ia32/SecEntry.nasm | 8 +++++++-
 OvmfPkg/Sec/X64/SecEntry.nasm  | 8 +++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/OvmfPkg/Sec/Ia32/SecEntry.nasm b/OvmfPkg/Sec/Ia32/SecEntry.nasm
index 03501969eb..fc7f47385a 100644
--- a/OvmfPkg/Sec/Ia32/SecEntry.nasm
+++ b/OvmfPkg/Sec/Ia32/SecEntry.nasm
@@ -40,6 +40,13 @@ extern ASM_PFX(SecCoreStartupWithStack)
 global ASM_PFX(_ModuleEntryPoint)
 ASM_PFX(_ModuleEntryPoint):
 
+    ;
+    ; Clear the CD (Cache Disable) flag in the CR0 register.
+    ;
+    mov     eax, cr0
+    and     eax, ~(1 << 30)
+    mov     cr0, eax
+
     ;
     ; Fill the temporary RAM with the initial stack value.
     ; The loop below will seed the heap as well, but that's harmless.
@@ -71,4 +78,3 @@ ASM_PFX(_ModuleEntryPoint):
     push    eax
     push    ebp
     call    ASM_PFX(SecCoreStartupWithStack)
-
diff --git a/OvmfPkg/Sec/X64/SecEntry.nasm b/OvmfPkg/Sec/X64/SecEntry.nasm
index d76adcffd8..7471b3a3e3 100644
--- a/OvmfPkg/Sec/X64/SecEntry.nasm
+++ b/OvmfPkg/Sec/X64/SecEntry.nasm
@@ -41,6 +41,13 @@ extern ASM_PFX(SecCoreStartupWithStack)
 global ASM_PFX(_ModuleEntryPoint)
 ASM_PFX(_ModuleEntryPoint):
 
+    ;
+    ; Clear the CD (Cache Disable) flag in the CR0 register.
+    ;
+    mov     rax, cr0
+    and     eax, ~(1 << 30)
+    mov     cr0, rax
+
     ;
     ; Fill the temporary RAM with the initial stack value.
     ; The loop below will seed the heap as well, but that's harmless.
@@ -72,4 +79,3 @@ ASM_PFX(_ModuleEntryPoint):
     mov     rdx, rsp
     sub     rsp, 0x20
     call    ASM_PFX(SecCoreStartupWithStack)
-
-- 
2.20.1