Naive questions regarding KVM

Naive questions regarding KVM

[Mathew Li]

Hi All,

I want to learn KVM code. Apologies for asking really simple
questions. I have Ubuntu 12.04 32bit installed on my laptop. As I
understand there are two modules of the KVM. One is called kvm.ko and
other arch specific e.g. in my case it is kvm-intel.ko. These modules
are already present in my system. I can do modinfo and it lists them.

What I want to do is modify KVM code to add print statements to
understand things better. But I don't know what code to modify and how
to rebuild these two modules for my system, so that they have my print
statements. Could you please guide me what code do I need to download
and how to compile that to get the modules regenerated for my system?
If I need to download the whole Linux kernel then where in Linux
kernel KVM code lives? I don't want to compile the whole linux kernel,
I just want to compile these modules for my system.

Thanks a lot for any help you could provide.

Thanks!
Matt

Re: Naive questions regarding KVM

[Jidong Xiao]

On Fri, May 23, 2014 at 12:57 AM, Mathew Li <mathew.li100@gmail.com> wrote:
> Hi All,
>
> I want to learn KVM code. Apologies for asking really simple
> questions. I have Ubuntu 12.04 32bit installed on my laptop. As I
> understand there are two modules of the KVM. One is called kvm.ko and
> other arch specific e.g. in my case it is kvm-intel.ko. These modules
> are already present in my system. I can do modinfo and it lists them.
>
> What I want to do is modify KVM code to add print statements to
> understand things better. But I don't know what code to modify and how
> to rebuild these two modules for my system, so that they have my print
> statements. Could you please guide me what code do I need to download
> and how to compile that to get the modules regenerated for my system?
> If I need to download the whole Linux kernel then where in Linux
> kernel KVM code lives? I don't want to compile the whole linux kernel,
> I just want to compile these modules for my system.
>
> Thanks a lot for any help you could provide.
>
> Thanks!
> Matt
If you are using the latest kernel, then arch/x86/kvm and virt/kvm are
the two directories you should look at, and also some header files are
under the include/linux directory. Since kvm is a part of the mainline
kernel, I don't think you need to download anything else other than
the mainline kernel. But, to use kvm, I think you should install Qemu,
which is a user-level tool.

If you compile kvm as a kernel module, then each time you insert your
printk statements, you don't need to compile the whole kernel, just
compile the specific directory you have made changes in. For example,
if you have changed arch/x86/kvm directory, you can use the command:
`make modules SUBDIRS=arch/x86/kvm`.

Once you are done, just copy the generated module: kvm.ko,
kvm-intel.ko to /lib/modules/your-kernel-version/kernel/arch/x86/kvm/.
Remove the existing kvm.ko/kvm-intel.ko, and install the new modules.

-Jidong

Re: Naive questions regarding KVM

[Mathew Li]

Thanks a lot Jidong. I will give it a run.

Thanks!
Matt

On Thu, May 22, 2014 at 10:12 PM, Jidong Xiao <jidong.xiao@gmail.com> wrote:
> On Fri, May 23, 2014 at 12:57 AM, Mathew Li <mathew.li100@gmail.com> wrote:
>> Hi All,
>>
>> I want to learn KVM code. Apologies for asking really simple
>> questions. I have Ubuntu 12.04 32bit installed on my laptop. As I
>> understand there are two modules of the KVM. One is called kvm.ko and
>> other arch specific e.g. in my case it is kvm-intel.ko. These modules
>> are already present in my system. I can do modinfo and it lists them.
>>
>> What I want to do is modify KVM code to add print statements to
>> understand things better. But I don't know what code to modify and how
>> to rebuild these two modules for my system, so that they have my print
>> statements. Could you please guide me what code do I need to download
>> and how to compile that to get the modules regenerated for my system?
>> If I need to download the whole Linux kernel then where in Linux
>> kernel KVM code lives? I don't want to compile the whole linux kernel,
>> I just want to compile these modules for my system.
>>
>> Thanks a lot for any help you could provide.
>>
>> Thanks!
>> Matt
> If you are using the latest kernel, then arch/x86/kvm and virt/kvm are
> the two directories you should look at, and also some header files are
> under the include/linux directory. Since kvm is a part of the mainline
> kernel, I don't think you need to download anything else other than
> the mainline kernel. But, to use kvm, I think you should install Qemu,
> which is a user-level tool.
>
> If you compile kvm as a kernel module, then each time you insert your
> printk statements, you don't need to compile the whole kernel, just
> compile the specific directory you have made changes in. For example,
> if you have changed arch/x86/kvm directory, you can use the command:
> `make modules SUBDIRS=arch/x86/kvm`.
>
> Once you are done, just copy the generated module: kvm.ko,
> kvm-intel.ko to /lib/modules/your-kernel-version/kernel/arch/x86/kvm/.
> Remove the existing kvm.ko/kvm-intel.ko, and install the new modules.
>
> -Jidong

Re: Naive questions regarding KVM

[Chai Wen]

On 05/23/2014 12:57 PM, Mathew Li wrote:

> Hi All,
> 
> I want to learn KVM code. Apologies for asking really simple
> questions. I have Ubuntu 12.04 32bit installed on my laptop. As I
> understand there are two modules of the KVM. One is called kvm.ko and
> other arch specific e.g. in my case it is kvm-intel.ko. These modules
> are already present in my system. I can do modinfo and it lists them.
> 
> What I want to do is modify KVM code to add print statements to
> understand things better. But I don't know what code to modify and how
> to rebuild these two modules for my system, so that they have my print
> statements. Could you please guide me what code do I need to download
> and how to compile that to get the modules regenerated for my system?
> If I need to download the whole Linux kernel then where in Linux
> kernel KVM code lives? I don't want to compile the whole linux kernel,
> I just want to compile these modules for my system.
> 
> Thanks a lot for any help you could provide.
>


Hi Li:

I happend to have an similar example for kernel-3.3.3.
If you want to build kvm modules out of a kernel tree you can copy files in kernel root dirs:
'arch/x86/kvm' and 'virt/kvm' to a dedicated dir like '/home/wrok/kvm_debug'.
Its Makefile could be like below.
Building command is some command like "make -C ../linux-3.3.3 M=`pwd` modules" in dir 'kvm_debug'

And trace.h & mmutrace.h need a littile change:
# [root@chaiw kvm_debug]# diff -U 5 trace.h ../linux-3.3.3/arch/x86/kvm/trace.h
# --- trace.h   2014-05-05 15:25:16.319200716 +0800
# +++ ../linux-3.3.3/arch/x86/kvm/trace.h       2012-04-23 06:39:43.000000000 +0800
# @@ -820,11 +820,11 @@
#                 __entry->gpa_match ? "GPA" : "GVA")
#  );
#  #endif /* _TRACE_KVM_H */
#
#  #undef TRACE_INCLUDE_PATH
# -#define TRACE_INCLUDE_PATH /home/work/kvm_debug
# +#define TRACE_INCLUDE_PATH arch/x86/kvm
#  #undef TRACE_INCLUDE_FILE
#  #define TRACE_INCLUDE_FILE trace
#
#  /* This part must be outside protection */
#  #include <trace/define_trace.h>
#
# [root@chaiw kvm_debug]# diff -U 5 mmutrace.h ../linux-3.3.3/arch/x86/kvm/mmutrace.h
# --- mmutrace.h        2014-05-05 15:28:19.300189943 +0800
# +++ ../linux-3.3.3/arch/x86/kvm/mmutrace.h    2012-04-23 06:39:43.000000000 +0800
# @@ -244,11 +244,11 @@
#                 __entry->access)
#  );
#  #endif /* _TRACE_KVMMMU_H */
#
#  #undef TRACE_INCLUDE_PATH
# -#define TRACE_INCLUDE_PATH /home/work/kvm_debug
# +#define TRACE_INCLUDE_PATH .
#  #undef TRACE_INCLUDE_FILE
#  #define TRACE_INCLUDE_FILE mmutrace
#
#  /* This part must be outside protection */
#  #include <trace/define_trace.h>


------- Makefile ---------
# depended on kernel-3.3.3
# for kvm module
kvm-y += kvm_main.o ioapic.o coalesced_mmio.o irq_comm.o eventfd.o \
         assigned-dev.o
kvm-$(CONFIG_IOMMU_API) += iommu.o
kvm-$(CONFIG_KVM_ASYNC_PF) += async_pf.o
kvm-y += x86.o mmu.o emulate.o i8259.o irq.o lapic.o i8254.o timer.o \
         cpuid.o pmu.o
obj-m := kvm.o

# for kvm_intel & kvm_amd modules
kvm_intel-y += vmx.o
kvm_amd-y += svm.o
obj-m += kvm_intel.o
obj-m += kvm_amd.o

clean:
        @-rm -f *.o
        @-rm -f *mod*
        @-rm -f *.ko


thanks
chai wen

 
> Thanks!
> Matt
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-- 
Regards

Chai Wen