linux-kernel - Re: [PATCH 1/4] KVM: x86: hyperv: Remove duplicate definitions of Reference TSC Page

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Message-ID: <874ktdrp5e.fsf@vitty.brq.redhat.com>
Date:   Tue, 21 Apr 2020 14:37:01 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     mikelley@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        sthemmin@...rosoft.com, wei.liu@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        pbonzini@...hat.com, sean.j.christopherson@...el.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Subject: Re: [PATCH 1/4] KVM: x86: hyperv: Remove duplicate definitions of Reference TSC Page

Michael Kelley <mikelley@...rosoft.com> writes:

> The Hyper-V Reference TSC Page structure is defined twice. struct
> ms_hyperv_tsc_page has padding out to a full 4 Kbyte page size. But
> the padding is not needed because the declaration includes a union
> with HV_HYP_PAGE_SIZE.  KVM uses the second definition, which is
> struct _HV_REFERENCE_TSC_PAGE, because it does not have the padding.
>
> Fix the duplication by removing the padding from ms_hyperv_tsc_page.
> Fix up the KVM code to use it. Remove the no longer used struct
> _HV_REFERENCE_TSC_PAGE.
>
> There is no functional change.
>
> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> ---
>  arch/x86/include/asm/hyperv-tlfs.h | 8 --------
>  arch/x86/include/asm/kvm_host.h    | 2 +-
>  arch/x86/kvm/hyperv.c              | 4 ++--
>  3 files changed, 3 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 29336574d0bc..0e4d76920957 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -303,7 +303,6 @@ struct ms_hyperv_tsc_page {
>  	u32 reserved1;
>  	volatile u64 tsc_scale;
>  	volatile s64 tsc_offset;
> -	u64 reserved2[509];
>  }  __packed;
>  
>  /*
> @@ -433,13 +432,6 @@ enum HV_GENERIC_SET_FORMAT {
>   */
>  #define HV_CLOCK_HZ (NSEC_PER_SEC/100)
>  
> -typedef struct _HV_REFERENCE_TSC_PAGE {
> -	__u32 tsc_sequence;
> -	__u32 res1;
> -	__u64 tsc_scale;
> -	__s64 tsc_offset;
> -}  __packed HV_REFERENCE_TSC_PAGE, *PHV_REFERENCE_TSC_PAGE;
> -
>  /* Define the number of synthetic interrupt sources. */
>  #define HV_SYNIC_SINT_COUNT		(16)
>  /* Define the expected SynIC version. */
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 42a2d0d3984a..4698343b9a05 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -865,7 +865,7 @@ struct kvm_hv {
>  	u64 hv_crash_param[HV_X64_MSR_CRASH_PARAMS];
>  	u64 hv_crash_ctl;
>  
> -	HV_REFERENCE_TSC_PAGE tsc_ref;
> +	struct ms_hyperv_tsc_page tsc_ref;
>  
>  	struct idr conn_to_evt;
>  
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index bcefa9d4e57e..1f3c6fd3cdaa 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -900,7 +900,7 @@ static int kvm_hv_msr_set_crash_data(struct kvm_vcpu *vcpu,
>   * These two equivalencies are implemented in this function.
>   */
>  static bool compute_tsc_page_parameters(struct pvclock_vcpu_time_info *hv_clock,
> -					HV_REFERENCE_TSC_PAGE *tsc_ref)
> +					struct ms_hyperv_tsc_page *tsc_ref)
>  {
>  	u64 max_mul;
>  
> @@ -941,7 +941,7 @@ void kvm_hv_setup_tsc_page(struct kvm *kvm,
>  	u64 gfn;
>  
>  	BUILD_BUG_ON(sizeof(tsc_seq) != sizeof(hv->tsc_ref.tsc_sequence));
> -	BUILD_BUG_ON(offsetof(HV_REFERENCE_TSC_PAGE, tsc_sequence) != 0);
> +	BUILD_BUG_ON(offsetof(struct ms_hyperv_tsc_page, tsc_sequence) != 0);
>  
>  	if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE))
>  		return;

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly