linux-kernel - Re: [PATCH v3 18/34] x86/hyperv: Fix 'struct hv_enlightened

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Message-ID: <a060d2f84fb207af7d96cb955dd676c1d87f6adb.camel@redhat.com>
Date:   Wed, 11 May 2022 14:30:23 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 18/34] x86/hyperv: Fix 'struct hv_enlightened_vmcs'
 definition

On Thu, 2022-04-14 at 15:19 +0200, Vitaly Kuznetsov wrote:
> Section 1.9 of TLFS v6.0b says:
> 
> "All structures are padded in such a way that fields are aligned
> naturally (that is, an 8-byte field is aligned to an offset of 8 bytes
> and so on)".
> 
> 'struct enlightened_vmcs' has a glitch:
> 
> ...
>         struct {
>                 u32                nested_flush_hypercall:1; /*   836: 0  4 */
>                 u32                msr_bitmap:1;         /*   836: 1  4 */
>                 u32                reserved:30;          /*   836: 2  4 */
>         } hv_enlightenments_control;                     /*   836     4 */
>         u32                        hv_vp_id;             /*   840     4 */
>         u64                        hv_vm_id;             /*   844     8 */
>         u64                        partition_assist_page; /*   852     8 */
> ...
> 
> And the observed values in 'partition_assist_page' make no sense at
> all. Fix the layout by padding the structure properly.
> 
> Fixes: 68d1eb72ee99 ("x86/hyper-v: define struct hv_enlightened_vmcs and clean field bits")
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/include/asm/hyperv-tlfs.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index 5225a85c08c3..e7ddae8e02c6 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -548,7 +548,7 @@ struct hv_enlightened_vmcs {
>  	u64 guest_rip;
>  
>  	u32 hv_clean_fields;
> -	u32 hv_padding_32;
> +	u32 padding32_1;
>  	u32 hv_synthetic_controls;
>  	struct {
>  		u32 nested_flush_hypercall:1;
> @@ -556,7 +556,7 @@ struct hv_enlightened_vmcs {
>  		u32 reserved:30;
>  	}  __packed hv_enlightenments_control;
>  	u32 hv_vp_id;
> -
> +	u32 padding32_2;
>  	u64 hv_vm_id;
>  	u64 partition_assist_page;
>  	u64 padding64_4[4];


Makes sense.

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky