Re: [edk2-devel] [PATCH 11/18] UefiCpuPkg: Disable PG in IA32 ApLoopCode

["Ni, Ray" <ray.ni@intel.com>]

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Reviewed-by: Ray Ni <ray.ni@intel.com>

Thanks,
Ray
________________________________
From: Tan, Dun <dun.tan@intel.com>
Sent: Friday, May 10, 2024 18:08
To: devel@edk2.groups.io <devel@edk2.groups.io>
Cc: Ni, Ray <ray.ni@intel.com>; Laszlo Ersek <lersek@redhat.com>; Kumar, Rahul R <rahul.r.kumar@intel.com>; Gerd Hoffmann <kraxel@redhat.com>; Wu, Jiaxin <jiaxin.wu@intel.com>
Subject: [PATCH 11/18] UefiCpuPkg: Disable PG in IA32 ApLoopCode

Disable paging in IA32 RelocateApLoop assembly
code to fix the issue that the AP page table is
unavailiable after boot OS under IA32 execution mode.

This issue exist in IA32 PEI + IA32 DXE normal boot
(also S3 boot with IA32 PEI after previous three commits
are accepted). In current MpLib code, the IA32 execution
mode code did not create page table in reserved memory
like what X64 code did. If PcdCpuStackGuard is TRUE, the
PG is enabled for AP in current RelocateApLoop assembly
code. And the page table for AP is unavailiable after
boot OS. This might cause potential issue. So disable PG
in IA32 RelocateApLoop.

Signed-off-by: Dun Tan <dun.tan@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Jiaxin Wu <jiaxin.wu@intel.com>
---
 UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm b/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
index d117f09ef5..75b18ce56f 100644
--- a/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
+++ b/UefiCpuPkg/Library/MpInitLib/Ia32/MpFuncs.nasm
@@ -225,6 +225,10 @@ RendezvousFunnelProcEnd:
 ;  specific to SEV-ES support and are not applicable on IA32.
 ;-------------------------------------------------------------------------------------
 AsmRelocateApLoopGenericStart:
+    mov        eax, cr0
+    btr        eax, 31             ; Clear CR0.PG
+    mov        cr0, eax            ; Disable paging since the page table might be unavailiable
+
     mov        eax, esp
     mov        esp, [eax + 12]     ; TopOfApStack
     push       dword [eax]         ; push return address for stack trace
--
2.31.1.windows.1



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