Message-Id: <5A2F9C260200007800196A92@prv-mh.provo.novell.com>
Date: Tue, 12 Dec 2017 01:06:46 -0700
From: "Jan Beulich" <JBeulich@suse.com>
To: "Maran Wilson" <maran.wilson@oracle.com>,
        "Paolo Bonzini" <pbonzini@redhat.com>
Cc: <andrew.cooper3@citrix.com>, <roger.pau@citrix.com>,
        <hch@infradead.org>, <x86@kernel.org>, <tglx@linutronix.de>,
        <xen-devel@lists.xenproject.org>, <boris.ostrovsky@oracle.com>,
        <mingo@redhat.com>, <rkrcmar@redhat.com>,
        "Juergen Gross" <jgross@suse.com>, <kvm@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <hpa@zytor.com>
Subject: Re: [RFC PATCH v2 1/2] xen/pvh: Add memory map pointer to
 hvm_start_info struct
References: <1512686715-11488-1-git-send-email-maran.wilson@oracle.com>
 <1512686715-11488-2-git-send-email-maran.wilson@oracle.com>
 <5A2A60130200007800195D10@prv-mh.provo.novell.com>
 <94195d5b-fb04-0e27-4fd5-ab3c13b58d07@redhat.com>
In-Reply-To: <94195d5b-fb04-0e27-4fd5-ab3c13b58d07@redhat.com>
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>>> On 11.12.17 at 22:59, <pbonzini@redhat.com> wrote:
> On 08/12/2017 09:49, Jan Beulich wrote:
>>> + * The layout of each entry in the memory map table is as follows and no
>>> + * padding is used between entries in the array:
>>> + *
>>> + *  0 +----------------+
>>> + *    | addr           | Base address
>>> + *  8 +----------------+
>>> + *    | size           | Size of mapping
>>> + * 16 +----------------+
>>> + *    | type           | E820_TYPE_xxx
>>> + * 20 +----------------|
>> I'm not convinced of re-using E820 types here. I can see that this
>> might ease the consumption in Linux, but I don't think there should
>> be any connection to x86 aspects here - the data being supplied is
>> x86-agnostic, and Linux'es placement of the header is also making
>> no connection to x86 (oddly enough, the current placement in the
>> Xen tree does, for a reason which escapes me).
> 
> FWIW, e820 types are now part of the ACPI standard.  So using them is
> not necessarily related to x86, and reasonably x86-agnostic.

Sort of - the description of it starts with "This interface is used in
real mode only on IA-PC-based systems ..."

But it being there is useful in another way: It shows that there's
an optional field making the full structure 64-bit aligned again. (It
at the same time shows - I admit I had forgotten about this aspect -
that the structure size isn't fixed in the first place, so consumers
have to convert [truncate/extend] the output to their internal
representation anyway, and hence there's even less of a reason
to tie the proposed structure's layout to the E820 one.)

Jan