Re: [Qemu-devel] Qemu deadlocks in tb_lock when using SVM+SoftMMU

[Alex Bennée]

Alexander Boettcher <address@hidden> writes:

> Hello,
>
> beginning with commit 3bd1d74576bacb120949e13cdeded7a0c792c685
>
> "cputlb: introduce tlb_flush_* async work"
>
> using Qemu with SoftMMU+SVM virtualization deadlocks because tb_lock is
> taken second time in cputlb.c tlb_flush_nocheck() function. The first
> time tb_lock is taken, according to my debugging, in cpu-exex.c
> tb_find() line 361.
>
> I'm using Qemu with:
>
> qemu-system-x86_64 -s -no-kvm -display sdl -m 512 -cpu phenom -nographic
> -cdrom genode.iso

I found the virtualbox.iso on your branch but I can't trigger the
assert. Running:

#!/bin/sh

QEMU="$@"

${QEMU} -s -no-kvm -display sdl -m 512 -cpu phenom -nographic -cdrom 
virtualbox.iso

I get:

NOVA Microhypervisor v7-2436fe2 (x86_32): Feb 25 2017 17:58:48 [gcc 4.9.2]
[init -> log_terminal]
[init -> log_terminal] [ 0] CORE:0:0:0 10:2:3:0 [0] AMD Phenom(tm) 9550 
Quad-Core Processor
qemu: fatal: invalid tss type
EAX=00000000 EBX=00000000 ECX=bffff000 EDX=00100000
ESI=00000000 EDI=00000000 EBP=00000000 ESP=bffff000
EIP=00100000 EFL=00000246 [---Z-P-] CPL=3 II=0 A20=1 SMM=0 HLT=0
ES =0023 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
CS =001b 00000000 ffffffff 00c0fb00 DPL=3 CS32 [-RA]
SS =0023 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
DS =0023 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
FS =0023 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
GS =0023 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
LDT=0000 00000000 00000000 00000000
TR =0030 cffffac0 00002540 00008b00 DPL=0 TSS32-busy
GDT=     cffff780 0000004f
IDT=     c001cb68 0000054f
CR0=8001003b CR2=00100000 CR3=026e9000 CR4=00000678
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 
DR3=0000000000000000
DR6=0000000000000000 DR7=0000000000000400
CCS=00000044 CCD=00000000 CCO=EFLAGS
EFER=0000000000001000
FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00000000cffff7800000004f00000000 XMM01=00000000c001cb680000054f00000000
XMM02=0000000000000000ffffffff0cf30023 XMM03=0000000000000000ffffffff0cf30023
XMM04=0000000000000000ffffffff0c9b0008 XMM05=0000000000000000ffffffff0c930010
XMM06=00000000cffffac000002540008b0030 XMM07=00000000000000000000000010000000
Aborted (core dumped)

Which is a guest error?


>
> When building with
> ./configure --target-list=x86_64-softmmu --enable-debug --disable-pie
> --enable-debug-tcg
>
> I get also a
>
> translate-all.c:165: tb_lock: Assertion `!have_tb_lock' failed.
>
> beginning with commit 3bd1d74576bacb120949e13cdeded7a0c792c685. Before
> the commit all is fine.
>
> Since I'm not very familiar with Qemu internals, it is not clear to me
> whether this commit breaks things or whether something must be
> handled/added special somewhere else. I attached below the backtrace of
> Qemu when it hangs in tb_lock.
>
> In [0] my branch based on 3bd1d74576bacb120949e13cdeded7a0c792c685 is
> used and [1] contains the iso image, if somebody wants try to reproduce it.
>
> [0] https://github.com/alex-ab/qemu/commits/genode_svm_issue
> [1]
> https://github.com/alex-ab/qemu/commit/1130fee3b04dd2bee576241de9a5771d6855b327
>
> Thanks in advance,
>
> Alex.


--
Alex Bennée