Re: [PATCH v3 3/4] Add a new hypercall to get the ESRT

From: Jan Beulich <jbeulich@suse.com>
To: Demi Marie Obenour <demi@invisiblethingslab.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v3 3/4] Add a new hypercall to get the ESRT
Date: Wed, 27 Apr 2022 10:56:34 +0200	[thread overview]
Message-ID: <3591eec7-1299-8783-26ad-ffe27bb9fdcd@suse.com> (raw)
In-Reply-To: <Yl7aC2a+TtOaFtqZ@itl-email>

On 19.04.2022 17:49, Demi Marie Obenour wrote:
> This hypercall can be used to get the ESRT from the hypervisor.  It
> returning successfully also indicates that Xen has reserved the ESRT and
> it can safely be parsed by dom0.

I'm not convinced of the need, and I view such an addition as inconsistent
with the original intentions. The pointer comes from the config table,
which Dom0 already has access to. All a Dom0 kernel may need to know in
addition is whether the range was properly reserved. This could be achieved
by splitting the EFI memory map entry in patch 2, instead of only splitting
the E820 derivation, as then XEN_FW_EFI_MEM_INFO can be used to find out
the range's type. Another way to find out would be for Dom0 to attempt to
map this area as MMIO, after first checking that no part of the range is in
its own memory allocation. This 2nd approach may, however, not really be
suitable for PVH Dom0, I think.

Jan