Re: [PATCH 0/3] x86/pvh: Support relocating dom0 kernel

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jason Andryuk <jason.andryuk@amd.com>
Cc: xen-devel@lists.xenproject.org,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Jan Beulich <jbeulich@suse.com>, Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH 0/3] x86/pvh: Support relocating dom0 kernel
Date: Thu, 7 Mar 2024 11:00:43 +0100	[thread overview]
Message-ID: <ZemQS-8a_a5pwzf-@macbook> (raw)
In-Reply-To: <20240306185032.103216-1-jason.andryuk@amd.com>

On Wed, Mar 06, 2024 at 01:50:29PM -0500, Jason Andryuk wrote:
> Xen tries to load a PVH dom0 kernel at the fixed guest physical address
> from the elf headers.  For Linux, this defaults to 0x1000000 (16MB), but
> it can be configured.
> 
> Unfortunately there exist firmwares that have reserved regions at this
> address, so Xen fails to load the dom0 kernel since it's not RAM.
> 
> The other issue is that the Linux PVH entry point is not
> position-independent.  It expects to run at the compiled
> CONFIG_PHYSICAL_ADDRESS.
> 
> This patch set expands the PVH dom0 builder to try to relocate the
> kernel if needed and possible.  XENFEAT_pvh_relocatable is added for
> kernels to indicate they are relocatable.  However, we may want to
> switch to an additional ELF note with the kernel alignment.  Linux
> specifies a kernel alignment in the bzImage boot_params.setup_header,
> but that is not present the ELF vmlinux file.

I wonder whether we need a pair of notes, to signal the min/max
addresses the kernel supports being relocated to.

Thanks, Roger.