linux-kernel - Question to hv_vtl_real_mode_header in hv

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Message-ID: <20240813172819.GA6572@yjiang5-mobl.amr.corp.intel.com>
Date: Tue, 13 Aug 2024 10:28:19 -0700
From: Yunhong Jiang <yunhong.jiang@...ux.intel.com>
To: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Question to hv_vtl_real_mode_header in hv_vtl.c

Hi, Srinivasan and Dexuan,
	I have a question to the hv_vtl_real_mode_header in
arch/x86//hyperv/hv_vtl.c when addressing one patch review comment.
	In hv_vtl_early_init(), the real_mode_header is set to
hv_vtl_real_mode_header, but there is no setup to the real_mode_header, since
the realmode_init() is marked x86_init_noop in hv_vtl_init_platform.
	How is the real_mode_header(in another word, hv_vtl_real_mode_header)
used? Is it to meet the access requirement from do_boot_cpu(), so that
real_mode_header->trampoline_start64 will work, although the start_ip is not
used?
	If it's really to support the do_boot_cpu() requirement, how does the
non-VTL guest meet the access requirement? The hv_vtl_init_platform() is
unconditionally called from ms_hyperv_init_platform(), so I assume all hyperv
guest will have the realmode_init() set as x86_init_noop.

Thank you
--jyh