From mboxrd@z Thu Jan  1 00:00:00 1970
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH v3] x86/hyper-v: Mark TLFS structures packed
Date: Wed, 12 Dec 2018 18:43:23 +0100
Message-ID: <87mupa4p50.fsf@vitty.brq.redhat.com>
References: <20181203140636.21912-1-vkuznets@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain
Cc: Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        linux-kernel@vger.kernel.org, Roman Kagan <rkagan@virtuozzo.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>, x86@kernel.org,
        "Michael Kelley \(EOSG\)" <Michael.H.Kelley@microsoft.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>
To: kvm@vger.kernel.org
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20181203140636.21912-1-vkuznets@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

Vitaly Kuznetsov <vkuznets@redhat.com> writes:

>  /* Define virtual processor assist page structure. */
>  struct hv_vp_assist_page {
> @@ -519,7 +519,7 @@ struct hv_vp_assist_page {
>  	__u64 nested_enlightenments_control[2];
>  	__u32 enlighten_vmentry;
>  	__u64 current_nested_vmcs;
> -};
> +} __packed;
>  

This particular structure wasn't properly padded: u32 padding is missing
between 'enlighten_vmentry' and 'current_nested_vmcs'.

>  struct hv_enlightened_vmcs {
>  	u32 revision_id;
> @@ -693,7 +693,7 @@ struct hv_enlightened_vmcs {
>  		u32 nested_flush_hypercall:1;
>  		u32 msr_bitmap:1;
>  		u32 reserved:30;
> -	} hv_enlightenments_control;
> +	}  __packed hv_enlightenments_control;
>  	u32 hv_vp_id;
>  
>  	u64 hv_vm_id;
> @@ -703,7 +703,7 @@ struct hv_enlightened_vmcs {
>  	u64 padding64_5[7];
>  	u64 xss_exit_bitmap;
>  	u64 padding64_6[7];
> -};
> +} __packed;

struct hv_enlightened_vmcs also has a hole: we need an u16 padding after
'u16 host_tr_selector'.

Both these problems led to Enlightened VMCS for Hyper-V on KVM being
completely broken.

As this is not yet merged, v4 is coming to rescue!

-- 
Vitaly