[edk2-devel] [PATCH] OvmfPkg/ResetVector: Fix assembler bit test flag check

[Lendacky, Thomas via groups.io]

Commit 63c50d3ff2854a76432b752af4f2a76f33ff1974 changed the check that is
used to determine if SEV-ES is active. Originally, a CMP instruction with
a supporting JZ instruction was used for the check. It was changed to use
the BT instruction but not JZ instruction. The result of a BT instruction
changes the the carry flag (CF) and not the zero flag (ZF). As a result,
the wrong condition is being checked. Update the JZ to a JNC to properly
detect if SEV-ES is active.

Fixes: 63c50d3ff285 ("OvmfPkg/ResetVector: cache the SEV status MSR...")
Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
---
 OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm b/OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm
index c5c683ebed3e..429a58c5efd3 100644
--- a/OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm
+++ b/OvmfPkg/ResetVector/Ia32/Flat32ToFlat64.asm
@@ -44,7 +44,7 @@ Transition32FlatTo64Flat:
 
     mov     ecx, 1
     bt      [SEV_ES_WORK_AREA_STATUS_MSR], ecx
-    jz      EnablePaging
+    jnc     EnablePaging
 
     ;
     ; SEV-ES is active, perform a quick sanity check against the reported
-- 
2.40.1



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