Re: [Qemu-devel] [PULL 08/10] target/arm: Conditionalize some asserts on aarch32 support

[Laszlo Ersek]

On 05/24/19 14:33, Laszlo Ersek wrote:
> Hi,
>
> On 11/02/18 18:16, Peter Maydell wrote:
>> From: Richard Henderson <address@hidden>
>>
>> When populating id registers from kvm, on a host that doesn't support
>> aarch32 mode at all, neither arm_div nor jazelle will be supported either.
>>
>> Signed-off-by: Richard Henderson <address@hidden>
>> Reviewed-by: Alex Bennée <address@hidden>
>> Tested-by: Alex Bennée <address@hidden>
>> Message-id: address@hidden
>> Reviewed-by: Peter Maydell <address@hidden>
>> Signed-off-by: Peter Maydell <address@hidden>
>> ---
>>  target/arm/cpu.h |  5 +++++
>>  target/arm/cpu.c | 15 +++++++++++++--
>>  2 files changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
>> index 8e6779936eb..b5eff79f73b 100644
>> --- a/target/arm/cpu.h
>> +++ b/target/arm/cpu.h
>> @@ -3296,6 +3296,11 @@ static inline bool isar_feature_aa64_fp16(const 
>> ARMISARegisters *id)
>>      return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, FP) == 1;
>>  }
>>
>> +static inline bool isar_feature_aa64_aa32(const ARMISARegisters *id)
>> +{
>> +    return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, EL0) >= 2;
>> +}
>> +
>>  static inline bool isar_feature_aa64_sve(const ARMISARegisters *id)
>>  {
>>      return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, SVE) != 0;
>> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
>> index 8f16e96b6c8..784a4c2dfcc 100644
>> --- a/target/arm/cpu.c
>> +++ b/target/arm/cpu.c
>> @@ -774,6 +774,7 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
>> **errp)
>>      CPUARMState *env = &cpu->env;
>>      int pagebits;
>>      Error *local_err = NULL;
>> +    bool no_aa32 = false;
>>
>>      /* If we needed to query the host kernel for the CPU features
>>       * then it's possible that might have failed in the initfn, but
>> @@ -820,6 +821,16 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
>> **errp)
>>              set_feature(env, ARM_FEATURE_V7VE);
>>          }
>>      }
>> +
>> +    /*
>> +     * There exist AArch64 cpus without AArch32 support.  When KVM
>> +     * queries ID_ISAR0_EL1 on such a host, the value is UNKNOWN.
>> +     * Similarly, we cannot check ID_AA64PFR0 without AArch64 support.
>> +     */
>> +    if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64)) {
>> +        no_aa32 = !cpu_isar_feature(aa64_aa32, cpu);
>> +    }
>> +
>>      if (arm_feature(env, ARM_FEATURE_V7VE)) {
>>          /* v7 Virtualization Extensions. In real hardware this implies
>>           * EL2 and also the presence of the Security Extensions.
>> @@ -829,7 +840,7 @@ static void arm_cpu_realizefn(DeviceState *dev, Error 
>> **errp)
>>           * Presence of EL2 itself is ARM_FEATURE_EL2, and of the
>>           * Security Extensions is ARM_FEATURE_EL3.
>>           */
>> -        assert(cpu_isar_feature(arm_div, cpu));
>> +        assert(no_aa32 || cpu_isar_feature(arm_div, cpu));
>
> The assertion above fails on my AArch64 host (APM Mustang A3). Meaning
> that my host CPU supports AArch32, but lacks "arm_div".
>
> (My understanding is that this commit, i.e., 0f8d06f16c9d, relaxed the
> assert originally added in commit 7e0cf8b47f0e ("target/arm: Convert
> division from feature bits to isar0 tests", 2018-10-24). Can we relax it
> even further?
>
> Better yet: can we rework the code to emit a warning, rather than
> aborting QEMU? Assertions are not the best tool IMHO for catching
> unusual (or slightly non-conformant / early) hardware.)

To clarify, I intended to launch a 32-bit ARM guest (with KVM
acceleration) on my AArch64 host.

Libvirt generated the following QEMU command line:

LC_ALL=C \
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin \
QEMU_AUDIO_DRV=none \
/opt/qemu-installed-optimized/bin/qemu-system-aarch64 \
  -name guest=f28.32bit,debug-threads=on \
  -S \
  -object 
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-2-f28.32bit/master-key.aes
 \
  -machine virt-4.1,accel=kvm,usb=off,dump-guest-core=off,gic-version=2 \
  -cpu host,aarch64=off \
  -drive file=/root/QEMU_EFI.fd.padded,if=pflash,format=raw,unit=0,readonly=on \
  -drive 
file=/var/lib/libvirt/qemu/nvram/f28.32bit_VARS.fd,if=pflash,format=raw,unit=1 \
  -m 8192 \
  -realtime mlock=off \
  -smp 8,sockets=8,cores=1,threads=1 \
  -uuid d525042e-1b37-4058-86ca-c6a2086e8485 \
  -no-user-config \
  -nodefaults \
  -chardev socket,id=charmonitor,fd=27,server,nowait \
  -mon chardev=charmonitor,id=monitor,mode=control \
  -rtc base=utc \
  -no-shutdown \
  -boot strict=on \
  -device 
pcie-root-port,port=0x8,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x1 
\
  -device pcie-root-port,port=0x9,chassis=2,id=pci.2,bus=pcie.0,addr=0x1.0x1 \
  -device pcie-root-port,port=0xa,chassis=3,id=pci.3,bus=pcie.0,addr=0x1.0x2 \
  -device pcie-root-port,port=0xb,chassis=4,id=pci.4,bus=pcie.0,addr=0x1.0x3 \
  -device pcie-root-port,port=0xc,chassis=5,id=pci.5,bus=pcie.0,addr=0x1.0x4 \
  -device pcie-root-port,port=0xd,chassis=6,id=pci.6,bus=pcie.0,addr=0x1.0x5 \
  -device qemu-xhci,id=usb,bus=pci.1,addr=0x0 \
  -device virtio-scsi-pci,id=scsi0,bus=pci.2,addr=0x0 \
  -device virtio-serial-pci,id=virtio-serial0,bus=pci.3,addr=0x0 \
  -drive 
file=/var/lib/libvirt/images/f28.32bit.root.qcow2,format=qcow2,if=none,id=drive-scsi0-0-0-0,werror=enospc,cache=writeback,discard=unmap
 \
  -device 
scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1,write-cache=on
 \
  -drive 
file=/var/lib/libvirt/images/f28.32bit.home.qcow2,format=qcow2,if=none,id=drive-scsi0-0-0-1,werror=enospc,cache=writeback,discard=unmap
 \
  -device 
scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=1,drive=drive-scsi0-0-0-1,id=scsi0-0-0-1,write-cache=on
 \
  -netdev tap,fd=29,id=hostnet0,vhost=on,vhostfd=30 \
  -device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:6f:d1:c8,bus=pci.4,addr=0x0,romfile=
 \
  -chardev pty,id=charserial0 \
  -serial chardev:charserial0 \
  -chardev socket,id=charchannel0,fd=31,server,nowait \
  -device 
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
 \
  -device usb-tablet,id=input0,bus=usb.0,port=1 \
  -device usb-kbd,id=input1,bus=usb.0,port=2 \
  -vnc 127.0.0.1:0 \
  -device virtio-gpu-pci,id=video0,max_outputs=1,bus=pci.5,addr=0x0 \
  -object rng-random,id=objrng0,filename=/dev/urandom \
  -device 
virtio-rng-pci,rng=objrng0,id=rng0,max-bytes=1048576,period=1000,bus=pci.6,addr=0x0
 \
  -msg timestamp=on

and then I got:

> qemu-system-aarch64: /root/src/upstream/qemu/target/arm/cpu.c:986:
> arm_cpu_realizefn: Assertion `no_aa32 || ({ ARMCPU *cpu_ = (cpu);
> isar_feature_arm_div(&cpu_->isar); })' failed.

QEMU was built at commit 8dc7fd56dd4f ("Merge remote-tracking branch
'remotes/philmd-gitlab/tags/fw_cfg-20190523-pull-request' into staging",
2019-05-23).

Thanks
Laszlo