linux-kernel - Re: [PATCH v1 0/6] KVM: VMX: Intel PT configuration switch using XSAVES/XRSTORS on VM-Entry/Exit

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Date:   Mon, 11 Nov 2019 14:28:14 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Luwei Kang <luwei.kang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, rkrcmar@...hat.com
Subject: Re: [PATCH v1 0/6] KVM: VMX: Intel PT configuration switch using
 XSAVES/XRSTORS on VM-Entry/Exit

On 16/05/19 10:25, Luwei Kang wrote:
> This patch set is mainly used for reduce the overhead of switch
> Intel PT configuation contex on VM-Entry/Exit by XSAVES/XRSTORS
> instructions.
> 
> I measured the cycles number of context witch on Manual and
> XSAVES/XRSTORES by rdtsc, and the data as below:
> 
> Manual save(rdmsr):     ~334  cycles
> Manual restore(wrmsr):  ~1668 cycles
> 
> XSAVES insturction:     ~124  cycles
> XRSTORS instruction:    ~378  cycles
> 
> Manual: Switch the configuration by rdmsr and wrmsr instruction,
>         and there have 8 registers need to be saved or restore.
>         They are IA32_RTIT_OUTPUT_BASE, *_OUTPUT_MASK_PTRS,
>         *_STATUS, *_CR3_MATCH, *_ADDR0_A, *_ADDR0_B,
>         *_ADDR1_A, *_ADDR1_B.
> XSAVES/XRSTORS: Switch the configuration context by XSAVES/XRSTORS
>         instructions. This patch set will allocate separate
>         "struct fpu" structure to save host and guest PT state.
>         Only a small portion of this structure will be used because
>         we only save/restore PT state (not save AVX, AVX-512, MPX,
>         PKRU and so on).
> 
> This patch set also do some code clean e.g. patch 2 will reuse
> the fpu pt_state to save the PT configuration contex and
> patch 3 will dymamic allocate Intel PT configuration state.
> 
> Luwei Kang (6):
>   x86/fpu: Introduce new fpu state for Intel processor trace
>   KVM: VMX: Reuse the pt_state structure for PT context
>   KVM: VMX: Dymamic allocate Intel PT configuration state
>   KVM: VMX: Allocate XSAVE area for Intel PT configuration
>   KVM: VMX: Intel PT configration context switch using XSAVES/XRSTORS
>   KVM: VMX: Get PT state from xsave area to variables
> 
>  arch/x86/include/asm/fpu/types.h |  13 ++
>  arch/x86/kvm/vmx/nested.c        |   2 +-
>  arch/x86/kvm/vmx/vmx.c           | 338 ++++++++++++++++++++++++++-------------
>  arch/x86/kvm/vmx/vmx.h           |  21 +--
>  4 files changed, 243 insertions(+), 131 deletions(-)
> 

Luwei, I found I had missed this series.  Can you check whether it needs
a rebase, since I don't have hardware that supports it?

Paolo