Re: Windows guest fails to boot into recovery mode due to commit 5267926

Andrew Fish

Stupid question? Is there a reason the page tables are not write protected and the write to the page table would fault?


Andrew Fish

On Mar 18, 2021, at 5:37 PM, Yao, Jiewen <jiewen.yao@...> wrote:

Hi Arie
I added some of my thought in the Bugzilla. -

If you can dump paging structure info for further analysis, we can help to check.

-----Original Message-----
From: <> On Behalf Of annie li
Sent: Friday, March 19, 2021 3:27 AM
To: Laszlo Ersek <lersek@...>;
Cc: Wang, Jian J <>; Andrew Fish <afish@...>;
Aaron Young <aaron.young@...>
Subject: Re: [edk2-discuss] Windows guest fails to boot into recovery mode due
to commit 5267926

Hello Laszlo,

In my previous email, the exception is reproduced with pretty old code base
from where I started bisecting the comments. This time I reproduce this issue
with the code of branch 'stable/202011' of upstream. All the log I am collecting
is from this code base(75ab038). Since the overall size of all log is pretty big, I'll
attach all the data you required in to this

I dump the register by qmp-regdump, and the result(regdump) is uploaded into
this bug. If this log doesn't suffice, can you please suggest the way you prefer?
The objdump is uploaded, as well as the details of page fault exception, please
check the details there.


-----Original Message-----
From: Laszlo Ersek [mailto:lersek@...]
Sent: Thursday, March 18, 2021 9:23 AM
To: Annie Li <>;
Cc:; Andrew Fish <afish@...>
Subject: Re: Windows guest fails to boot into recovery mode due to commit

On 03/18/21 02:48, Annie Li wrote:

I ran into a windows booting failure issue(a page fault exception),
and narrow down it to the following patch,
MdeModulePkg/DxeIpl: support more NX related PCDs

This issue always happens after QMP is terminated by <ctrl-C> twice, see
following steps.

1. Boot Windows VM up, and <ctrl-C> to exit the QMP

2. Repeat 1

3. Boot Windows VM, and this page fault issue happens. (Note: Windows
should boot into recovery mode in this round, and this is due to the previous two
consecutive boot failure, see

During above 3 windows booting procedures, the value of following
variables are always the same, PcdSetNxForStack 0
PcdDxeNxMemoryProtectionPolicy 0 PcdImageProtectionPolicy 2

However, Windows guest fails to boot up into recovery mode in the 3rd round
due to the patch above(5267926). I modified the return value to "(PcdGetBool
(PcdSetNxForStack)" in function "IsEnableNonExecNeeded" in
MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c, this page fault issue is
gone with this change. The patch(5267926) is for fixing bug
sjSaIZXk_W_MusXNUlQBxGqsJBTLSxdsog$ , where the comments show
PcdImageProtectionPolicy needs also to enable NXE. But this does cause the
page fault exception in this scenario, any suggestion?

The page fault exception is pasted here,

!!!! X64 Exception Type - 0E(#PF - Page-Fault) CPU Apic ID - 00000000 !!!!
ExceptionData - 0000000000000009 I:0 R:1 U:0 W:0 P:1 PK:0 SS:0 SGX:0
RIP - 000000003E0A7C75, CS - 0000000000000038, RFLAGS -
0000000000010202 RAX - 8000000000000003, RCX - 0000000000000001, RDX
- 0000000001040001 RBX - 0000000000000001, RSP - 00000000001A6AA0,
RBP - 0000000001040001 RSI - 000000003F2E2010, RDI - 0000000000000001
R8 - 0000000000000000, R9 - 000000003E0AEC90, R10 - 0000FFFFFFFFF000
R11 - 00000000001A6E90, R12 - 0000000000000000, R13 -
R14 - 00000000001A6B28, R15 - 00000000001AB000
DS - 0000000000000030, ES - 0000000000000030, FS - 0000000000000030
GS - 0000000000000030, SS - 0000000000000030
CR0 - 0000000080010033, CR2 - 000000003F2E2010, CR3 -
CR4 - 0000000000040668, CR8 - 0000000000000000
DR0 - 0000000000000000, DR1 - 0000000000000000, DR2 -
DR3 - 0000000000000000, DR6 - 00000000FFFF0FF0, DR7 -
0000000000000400 GDTR - 000000003F1EE698 0000000000000047, LDTR -
IDTR - 000000003ECCA018 0000000000000FFF, TR - 0000000000000000
FXSAVE_STATE - 00000000001A6700
!!!! Find image based on IP(0x3E0A7C75) /builddir/build/BUILD/edk2-
(ImageBase=000000003E0A5000, EntryPoint=000000003E0A86E8) !!!!

In addition to what Andrew said, I suggest the following:

(1) Please rebuild OVMF *locally*, using the same edk2 tree, and the same
toolchain, and the same "build" flags.

(2) Reproduce the issue, capture the register dump.

(3) Run the following command:

objdump -f -S

The point of this exercise is to reproduce the issue with such an OVMF build for
which you have a matching "TerminalDxe.debug" file. Once you do that, you can
run "objdump" on the ".debug" file, and get a disassembly of the TerminalDxe
driver, inter-leaved with the C language source code.

Then, we can do two things:

- we can verify whether (EntryPoint - ImageBase), from the register dump,
matches the (relative) "start address" that "objdump -f" reports,

- we can take the crash offset (RIP - ImageBase), from the register dump, and
use that offset into the "objdump -S" disassembly, to narrow down what the
terminal driver may have been doing to trigger the crash.

It's not necessarily the terminal driver's fault that encounter a crash, but
knowing what TerminalDxe was up to, might shed light on the actual reason. It's
of course also possible that TerminalDxe *is* at fault. We'll see.

If possible, please post:
- your precise edk2 version (if you have local patches, it would be best to
reproduce with an upstream-only tree),
- your full firmware log (feel free to compress it),
- the register dump from serial,
- the objdump (disassembly) output (feel free to compress it).


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