Re: [Xen-devel] [PATCH v3 14/14] xen/mm: Provide dummy M2P-related helpers when !CONFIG_HAVE_M2P

From: "Jan Beulich" <JBeulich@suse.com>
To: "Julien Grall" <julien.grall@arm.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>, WeiLiu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>,
	george.dunlap@citrix.com, Tim Deegan <tim@xen.org>,
	xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH v3 14/14] xen/mm: Provide dummy M2P-related helpers when !CONFIG_HAVE_M2P
Date: Wed, 05 Jun 2019 05:07:20 -0600	[thread overview]
Message-ID: <5CF7A268020000780023579B@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <20190603160350.29806-15-julien.grall@arm.com>

>>> On 03.06.19 at 18:03, <julien.grall@arm.com> wrote:
> At the moment, Arm is providing a dummy implementation for the M2P
> helpers used in common code. However, they are quite isolated and could
> be used by other architecture in the future. So move all the helpers in
> xen/mm.h.

And where's the problem then adding ...

> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -655,4 +655,18 @@ static inline void share_xen_page_with_privileged_guests(
>      share_xen_page_with_guest(page, dom_xen, flags);
>  }
>  
> +/*
> + * Dummy implementation of M2P-related helpers for common code when
> + * the architecture doesn't have an M2P.
> + */
> +#ifndef CONFIG_HAS_M2P
> +
> +#define INVALID_M2P_ENTRY        (~0UL)
> +#define SHARED_M2P_ENTRY         (~0UL - 1UL)
> +#define SHARED_M2P(_e)           ((_e) == SHARED_M2P_ENTRY)
> +
> +static inline void set_pfn_from_mfn(mfn_t mfn, unsigned long pfn) {}
> +
> +#endif

... mfn_to_gmfn() to this set? Perhaps a declaration without any
definition anywhere?

Also please take the opportunity and drop the unnecessary underscore
from _e. And actually, shouldn't this uniformly return false? At which
point you don't even need SHARED_M2P_ENTRY.

Jan

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