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id = 661
title = "Unable to enable 5 level paging"
state = "closed"
created_at = "2021-10-10T20:46:52.187Z"
closed_at = "2022-08-03T14:55:39.489Z"
labels = ["Regression", "Stable::to backport", "accel: TCG", "target: i386"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/661"
host-os = "Arch Linux"
host-arch = "x86"
qemu-version = "QEMU emulator version 6.1.0"
guest-os = "https://github.com/ethan4984/rock https://github.com/limine-bootloader/limine"
guest-arch = "x86"
description = """When attempting to set cr4.LA57, qemu just freezes on that instruction. When I say freeze I mean literally freeze, no exceptions, nothing, it just halts forever on that instruction. When this happened, the first thing I did was
```
(qemu) info registers
EAX=00001000 EBX=00000001 ECX=80224f08 EDX=00000000
ESI=8034a3a0 EDI=00026520 EBP=000079f8 ESP=000079c8
EIP=00019648 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0020 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
CS =0018 00000000 ffffffff 00c09a00 DPL=0 CS32 [-R-]
SS =0020 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
DS =0020 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
FS =0020 00000000 ffffffff 00cf9300 DPL=0 DS [-WA]
GS =0020 00000000 ffffffff 00cf9300 DPL=0 DS [-WA]
LDT=0000 00000000 00000000 00008200 DPL=0 LDT
TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
GDT= 0000e120 00000037
IDT= 00000000 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000
DR6=00000000ffff0ff0 DR7=0000000000000400
EFER=0000000000000000
...
```
then using gdb to figure out what instruction it is hanging on, I set a breakpoint at 0x19648 at and ran
```
(gdb) x/1 0x19648
=> 0x19648:\tmov %rax,%cr4
(gdb)
```
This instruction corresponds to this LOC within limine https://github.com/limine-bootloader/limine/blob/trunk/stage23/protos/stivale.32.c#L33"""
reproduce = """1. Try to enable 5 level paging
2. qemu freezes when trying to set cr4.LA57
3. cry"""
additional = """This never happened prior to version 6.1, I test this on multiple different machines and a few of my friends
experienced the same issue
I have not tested this on linux, however I assume it will do the same on anything else.
Either way, qemu should not be just halting"""
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