Re: [PATCH for-5.1 V4 1/4] hw/mips: Implement the kvm_type() hook in MachineClass

[Huacai Chen]

Hi, Thomas and Aleksandar,

On Tue, Jun 16, 2020 at 3:45 AM Aleksandar Markovic
<aleksandar.m.mail@gmail.com> wrote:
>
> On Mon, Jun 15, 2020 at 10:55 AM Thomas Huth <thuth@redhat.com> wrote:
> >
> > On 15/06/2020 02.52, Huacai Chen wrote:
> > > Hi, Aleksandar,
> > >
> > > On Sun, Jun 14, 2020 at 4:07 PM Aleksandar Markovic
> > > <aleksandar.qemu.devel@gmail.com> wrote:
> > >>
> > >>
> > >>
> > >> уто, 2. јун 2020. у 04:38 Huacai Chen <zltjiangshi@gmail.com> је 
> > >> написао/ла:
> > >>>
> > >>> MIPS has two types of KVM: TE & VZ, and TE is the default type. Now we
> > >>> can't create a VZ guest in QEMU because it lacks the kvm_type() hook in
> > >>> MachineClass. Besides, libvirt uses a null-machine to detect the kvm
> > >>> capability, so by default it will return "KVM not supported" on a VZ
> > >>> platform. Thus, null-machine also need the kvm_type() hook.
> > >>>
> > >>> Reviewed-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
> > >>> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> > >>> Co-developed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> > >>> ---
> > >>
> > >> Huacai,
> > >>
> > >> Please take a look at Peter's remarks at:
> > >>
> > >> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg01878.html
> > >>
> > >> ...and refactor this patch for v5. My general advice: The simpler, the 
> > >> batter.
> > >>
> > > OK, I will rework this patch.
> >
> >  Hi,
> >
> > is there maybe also a way to do this without moving null-machine.o from
> > common-obj-y to obj-y, and to avoid the target-specific hacks in this
> > file ? We just moved the null-machine from obj-y to common-obj-y two
> > years ago (see commit 3858ff763985fb9e), since it's more desirable to
> > have as much code in common-obj to save compilation time and maybe to be
> > able to link a qemu with more than one target CPU in one binary one day...
> >
> > ppc64 has also more than one kvm_type (kvm-hv and kvm-pr), and
> > apparently it also works without hacks to the null-machine code there
> > ... so maybe you can peek into the ppc64 code to see how it is solved there?
> >
>
> Hi, Huacai,
>
> I think the optimal outcome for this release of QEMU would be if you
> drop support for VZ. I think your scenario could work without VZ,
> couldn't it?
>
> This is a fairly complex thing, and, as you see, it is a little
> intrusive, it could negatively impact other targets. With enough
> development time, you can easily provide that support in 5.2. - but
> now we are close to 5.1 softfreeze.
>
> Even without VZ support, I would consider your contribution the most
> significant for MIPS target in last two years, at least - a giant step
> ahead!
There are two problems: 1, qemu need kvm_type() to create a normal KVM
guest. 2, libvirt use the null-machine to detect the KVM capability.
For the first problem, just provide a kvm_type() hook for MIPS is
enough, which is similar to ppc64. For the second problem, I think
libvirt is also unable to detect the KVM capabilty on ppc64, unless
ppc64 do the same hack on null-machine.

V5 of this patch will only provide kvm_type() for MIPS (not hack
null-machine.c), but all of us should think how to solve the second
problem.

Huacai
>
> Best Regards,
> Aleksandar
>
> >  Thomas
> >
> >
> > >>>  hw/core/Makefile.objs  |  2 +-
> > >>>  hw/core/null-machine.c |  4 ++++
> > >>>  hw/mips/Makefile.objs  |  2 +-
> > >>>  hw/mips/common.c       | 42 ++++++++++++++++++++++++++++++++++++++++++
> > >>>  include/hw/mips/mips.h |  3 +++
> > >>>  5 files changed, 51 insertions(+), 2 deletions(-)
> > >>>  create mode 100644 hw/mips/common.c
> > >>>
> > >>> diff --git a/hw/core/Makefile.objs b/hw/core/Makefile.objs
> > >>> index 1d540ed..b5672f4 100644
> > >>> --- a/hw/core/Makefile.objs
> > >>> +++ b/hw/core/Makefile.objs
> > >>> @@ -17,11 +17,11 @@ common-obj-$(CONFIG_SOFTMMU) += 
> > >>> vm-change-state-handler.o
> > >>>  common-obj-$(CONFIG_SOFTMMU) += qdev-properties-system.o
> > >>>  common-obj-$(CONFIG_SOFTMMU) += sysbus.o
> > >>>  common-obj-$(CONFIG_SOFTMMU) += machine.o
> > >>> -common-obj-$(CONFIG_SOFTMMU) += null-machine.o
> > >>>  common-obj-$(CONFIG_SOFTMMU) += loader.o
> > >>>  common-obj-$(CONFIG_SOFTMMU) += machine-hmp-cmds.o
> > >>>  common-obj-$(CONFIG_SOFTMMU) += numa.o
> > >>>  common-obj-$(CONFIG_SOFTMMU) += clock-vmstate.o
> > >>> +obj-$(CONFIG_SOFTMMU) += null-machine.o
> > >>>  obj-$(CONFIG_SOFTMMU) += machine-qmp-cmds.o
> > >>>
> > >>>  common-obj-$(CONFIG_EMPTY_SLOT) += empty_slot.o
> > >>> diff --git a/hw/core/null-machine.c b/hw/core/null-machine.c
> > >>> index cb47d9d..94a36f9 100644
> > >>> --- a/hw/core/null-machine.c
> > >>> +++ b/hw/core/null-machine.c
> > >>> @@ -17,6 +17,7 @@
> > >>>  #include "sysemu/sysemu.h"
> > >>>  #include "exec/address-spaces.h"
> > >>>  #include "hw/core/cpu.h"
> > >>> +#include "hw/mips/mips.h"
> > >>>
> > >>>  static void machine_none_init(MachineState *mch)
> > >>>  {
> > >>> @@ -50,6 +51,9 @@ static void machine_none_machine_init(MachineClass 
> > >>> *mc)
> > >>>      mc->max_cpus = 1;
> > >>>      mc->default_ram_size = 0;
> > >>>      mc->default_ram_id = "ram";
> > >>> +#ifdef TARGET_MIPS
> > >>> +    mc->kvm_type = mips_kvm_type;
> > >>> +#endif
> > >>>  }
> > >>>
> > >>>  DEFINE_MACHINE("none", machine_none_machine_init)
> > >>> diff --git a/hw/mips/Makefile.objs b/hw/mips/Makefile.objs
> > >>> index 739e2b7..3b3e6ea 100644
> > >>> --- a/hw/mips/Makefile.objs
> > >>> +++ b/hw/mips/Makefile.objs
> > >>> @@ -1,4 +1,4 @@
> > >>> -obj-y += addr.o mips_int.o
> > >>> +obj-y += addr.o common.o mips_int.o
> > >>>  obj-$(CONFIG_R4K) += r4k.o
> > >>>  obj-$(CONFIG_MALTA) += gt64xxx_pci.o malta.o
> > >>>  obj-$(CONFIG_MIPSSIM) += mipssim.o
> > >>> diff --git a/hw/mips/common.c b/hw/mips/common.c
> > >>> new file mode 100644
> > >>> index 0000000..4d8e141
> > >>> --- /dev/null
> > >>> +++ b/hw/mips/common.c
> > >>> @@ -0,0 +1,42 @@
> > >>> +/*
> > >>> + * Common MIPS routines
> > >>> + *
> > >>> + * Copyright (c) 2020 Huacai Chen (chenhc@lemote.com)
> > >>> + * This code is licensed under the GNU GPL v2.
> > >>> + */
> > >>> +
> > >>> +#include <linux/kvm.h>
> > >>> +#include "qemu/osdep.h"
> > >>> +#include "qemu-common.h"
> > >>> +#include "hw/boards.h"
> > >>> +#include "hw/mips/mips.h"
> > >>> +#include "sysemu/kvm_int.h"
> > >>> +
> > >>> +#ifndef CONFIG_KVM
> > >>> +
> > >>> +int mips_kvm_type(MachineState *machine, const char *vm_type)
> > >>> +{
> > >>> +    return 0;
> > >>> +}
> > >>> +
> > >>> +#else
> > >>> +
> > >>> +int mips_kvm_type(MachineState *machine, const char *vm_type)
> > >>> +{
> > >>> +    int r;
> > >>> +    KVMState *s = KVM_STATE(machine->accelerator);
> > >>> +
> > >>> +    r = kvm_check_extension(s, KVM_CAP_MIPS_VZ);
> > >>> +    if (r > 0) {
> > >>> +        return KVM_VM_MIPS_VZ;
> > >>> +    }
> > >>> +
> > >>> +    r = kvm_check_extension(s, KVM_CAP_MIPS_TE);
> > >>> +    if (r > 0) {
> > >>> +        return KVM_VM_MIPS_TE;
> > >>> +    }
> > >>> +
> > >>> +    return -1;
> > >>> +}
> > >>> +
> > >>> +#endif
> > >>> diff --git a/include/hw/mips/mips.h b/include/hw/mips/mips.h
> > >>> index 0af4c3d..2ac0580 100644
> > >>> --- a/include/hw/mips/mips.h
> > >>> +++ b/include/hw/mips/mips.h
> > >>> @@ -20,4 +20,7 @@ void rc4030_dma_write(void *dma, uint8_t *buf, int 
> > >>> len);
> > >>>
> > >>>  DeviceState *rc4030_init(rc4030_dma **dmas, IOMMUMemoryRegion 
> > >>> **dma_mr);
> > >>>
> > >>> +/* common.c */
> > >>> +int mips_kvm_type(MachineState *machine, const char *vm_type);
> > >>> +
> > >>>  #endif
> > >>> --
> > >>> 2.7.0
> > >>>
> > >
> >
> >