linux-kernel - Re: [PATCH v2 0/6] kvm: x86: export TSC information to user-space

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Date:   Fri, 16 Sep 2016 16:56:34 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Luiz Capitulino <lcapitulino@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rkrcmar@...hat.com,
        rostedt@...dmis.org, mhiramat@...nel.org, mtosatti@...hat.com
Subject: Re: [PATCH v2 0/6] kvm: x86: export TSC information to user-space



On 16/09/2016 16:27, Luiz Capitulino wrote:
> [Introduction will follow]
> 
> Changelog
> ---------
> 
> v2
> 
>  - add tsc_offset field to struct kvm_vcpu_arch
>  - drop read_tsc_offset()
>  - add per-vcpu dir entries in debugfs
>  - export TSC scaling info (besides TSC offset)
>  - export the TSC offset as a signed number
>  - drop patch that wrongly tried to improve error
>    handling in kvm_create_vm_debugfs()

I've tested this patch on an AMD machine with TSC scaling, so I'm
pushing it shortly to kvm/queue.

Paolo

> Intro
> -----
> 
> This series exports a VM's TSC offset and TSC scaling
> information to user-space via a new per-vcpu directory
> in debugfs. For example:
> 
>   /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-offset
>   /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-scaling-ratio
>   /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-scaling-ratio-frac-bits
> 
> The TSC offset in particular is needed in user-space
> in order for tracing tools, such as trace-cmd, to be
> able to merge the host and guest traces using the
> host TSC. This is explained in detail in this thread:
> 
>   [Qemu-devel] [RFC] host and guest kernel trace merging
>   https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg00887.html
> 
> Luiz Capitulino (6):
>   kvm: x86: add tsc_offset field to struct kvm_vcpu_arch
>   kvm: x86: drop read_tsc_offset()
>   kvm: kvm_destroy_vm_debugfs(): check debugfs_stat_data pointer
>   kvm: add stubs for arch specific debugfs support
>   kvm: create per-vcpu dirs in debugfs
>   kvm: x86: export TSC information to user-space
> 
>  arch/arm/kvm/arm.c              | 10 ++++++
>  arch/mips/kvm/mips.c            | 10 ++++++
>  arch/powerpc/kvm/powerpc.c      | 10 ++++++
>  arch/s390/kvm/kvm-s390.c        | 10 ++++++
>  arch/x86/include/asm/kvm_host.h |  2 +-
>  arch/x86/kvm/Makefile           |  2 +-
>  arch/x86/kvm/debugfs.c          | 69 +++++++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/svm.c              |  8 -----
>  arch/x86/kvm/vmx.c              |  6 ----
>  arch/x86/kvm/x86.c              | 12 +++++--
>  include/linux/kvm_host.h        |  4 +++
>  virt/kvm/kvm_main.c             | 40 ++++++++++++++++++++++--
>  12 files changed, 161 insertions(+), 22 deletions(-)
>  create mode 100644 arch/x86/kvm/debugfs.c
>