Re: [PATCH v2] target/arm: Check supported KVM features globally (not per vCPU)

[Andrew Jones]

On Fri, Jun 19, 2020 at 11:55:42AM +0200, Philippe Mathieu-Daudé wrote:
> Since commit d70c996df23f, when enabling the PMU we get:
> 
>   $ qemu-system-aarch64 -cpu host,pmu=on -M virt,accel=kvm,gic-version=3
>   Segmentation fault (core dumped)
> 
>   Thread 1 "qemu-system-aar" received signal SIGSEGV, Segmentation fault.
>   0x0000aaaaaae356d0 in kvm_ioctl (s=0x0, type=44547) at 
> accel/kvm/kvm-all.c:2588
>   2588        ret = ioctl(s->fd, type, arg);
>   (gdb) bt
>   #0  0x0000aaaaaae356d0 in kvm_ioctl (s=0x0, type=44547) at 
> accel/kvm/kvm-all.c:2588
>   #1  0x0000aaaaaae31568 in kvm_check_extension (s=0x0, extension=126) at 
> accel/kvm/kvm-all.c:916
>   #2  0x0000aaaaaafce254 in kvm_arm_pmu_supported (cpu=0xaaaaac214ab0) at 
> target/arm/kvm.c:213
>   #3  0x0000aaaaaafc0f94 in arm_set_pmu (obj=0xaaaaac214ab0, value=true, 
> errp=0xffffffffe438) at target/arm/cpu.c:1111
>   #4  0x0000aaaaab5533ac in property_set_bool (obj=0xaaaaac214ab0, 
> v=0xaaaaac223a80, name=0xaaaaac11a970 "pmu", opaque=0xaaaaac222730, 
> errp=0xffffffffe438) at qom/object.c:2170
>   #5  0x0000aaaaab5512f0 in object_property_set (obj=0xaaaaac214ab0, 
> v=0xaaaaac223a80, name=0xaaaaac11a970 "pmu", errp=0xffffffffe438) at 
> qom/object.c:1328
>   #6  0x0000aaaaab551e10 in object_property_parse (obj=0xaaaaac214ab0, 
> string=0xaaaaac11b4c0 "on", name=0xaaaaac11a970 "pmu", errp=0xffffffffe438) 
> at qom/object.c:1561
>   #7  0x0000aaaaab54ee8c in object_apply_global_props (obj=0xaaaaac214ab0, 
> props=0xaaaaac018e20, errp=0xaaaaabd6fd88 <error_fatal>) at qom/object.c:407
>   #8  0x0000aaaaab1dd5a4 in qdev_prop_set_globals (dev=0xaaaaac214ab0) at 
> hw/core/qdev-properties.c:1218
>   #9  0x0000aaaaab1d9fac in device_post_init (obj=0xaaaaac214ab0) at 
> hw/core/qdev.c:1050
>   ...
>   #15 0x0000aaaaab54f310 in object_initialize_with_type (obj=0xaaaaac214ab0, 
> size=52208, type=0xaaaaabe237f0) at qom/object.c:512
>   #16 0x0000aaaaab54fa24 in object_new_with_type (type=0xaaaaabe237f0) at 
> qom/object.c:687
>   #17 0x0000aaaaab54fa80 in object_new (typename=0xaaaaabe23970 
> "host-arm-cpu") at qom/object.c:702
>   #18 0x0000aaaaaaf04a74 in machvirt_init (machine=0xaaaaac0a8550) at 
> hw/arm/virt.c:1770
>   #19 0x0000aaaaab1e8720 in machine_run_board_init (machine=0xaaaaac0a8550) 
> at hw/core/machine.c:1138
>   #20 0x0000aaaaaaf95394 in qemu_init (argc=5, argv=0xffffffffea58, 
> envp=0xffffffffea88) at softmmu/vl.c:4348
>   #21 0x0000aaaaaada3f74 in main (argc=<optimized out>, argv=<optimized out>, 
> envp=<optimized out>) at softmmu/main.c:48
> 
> This is because in frame #2, cpu->kvm_state is still NULL
> (the vCPU is not yet realized).
> 
> KVM has a hard requirement of all cores supporting the same
> feature set. We only need to check if the accelerator supports
> a feature, not each vCPU individually.
> 
> Fix by kvm_arm_<FEATURE>_supported() functions take a AccelState
> argument (already realized/valid at this point) instead of a
> CPUState argument.
> 
> Reported-by: Haibo Xu <haibo.xu@linaro.org>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> v2: Use global kvm_state (bonzini)
> 
> Paolo, does this break migration of encrypted memory assumptions?
> 
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Supersedes: <20200617130800.26355-1-philmd@redhat.com>
> ---
>  target/arm/kvm_arm.h | 21 +++++++++------------
>  target/arm/cpu.c     |  2 +-
>  target/arm/cpu64.c   | 10 +++++-----
>  target/arm/kvm.c     |  4 ++--
>  target/arm/kvm64.c   | 14 +++++---------
>  5 files changed, 22 insertions(+), 29 deletions(-)
>

Hi Phil,

Can you also post the attached patch with this one (a two patch series)?
I want to ensure the bug is fixed before the test gets merged, but I
also would like the test to be added in order to catch things like this
in the future.

Thanks,
drew

0001-tests-qtest-arm-cpu-features-Add-feature-setting-tes.patch
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