linux-kernel - Re: Question to hv_vtl_real_mode_header in hv

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Message-ID: <20240824160202.GA18333@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Sat, 24 Aug 2024 09:02:02 -0700
From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To: Wei Liu <wei.liu@...nel.org>
Cc: Yunhong Jiang <yunhong.jiang@...ux.intel.com>, kys@...rosoft.com,
	haiyangz@...rosoft.com, decui@...rosoft.com,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Question to hv_vtl_real_mode_header in hv_vtl.c

On Fri, Aug 23, 2024 at 10:41:22PM +0000, Wei Liu wrote:
> On Tue, Aug 13, 2024 at 02:36:28PM -0700, Yunhong Jiang wrote:
> > On Tue, Aug 13, 2024 at 10:28:19AM -0700, Yunhong Jiang wrote:
> > > 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.
> > 
> > The patch review mentioned above is
> > https://lore.kernel.org/lkml/87a5ho2q6x.ffs@tglx/ . Can we set real_mode_header
> > to hv_vtl_real_mode_header in hv_vtl_init_platform(), instead of
> > hv_vtl_early_init()?

Yes, fine to move.

- Saurabh