linux-kernel - Re: [Xen-devel] [PATCH] xen/pvh: Indicate XENFEAT_linux_rsdp

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Message-ID: <20180410083544.q54rapngqie4ler3@citrix.com>
Date:   Tue, 10 Apr 2018 09:35:44 +0100
From:   Wei Liu <wei.liu2@...rix.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:     <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
        <jgross@...e.com>, Wei Liu <wei.liu2@...rix.com>
Subject: Re: [Xen-devel] [PATCH] xen/pvh: Indicate
 XENFEAT_linux_rsdp_unrestricted to Xen

On Mon, Apr 09, 2018 at 02:51:44PM -0400, Boris Ostrovsky wrote:
> Pre-4.17 kernels ignored start_info's rsdp_paddr pointer and instead
> relied on finding RSDP in standard location in BIOS RO memory. This
> has worked since that's where Xen used to place it.
> 
> However, with recent Xen change (commit 4a5733771e6f ("libxl: put RSDP
> for PVH guest near 4GB")) it prefers to keep RSDP at a "non-standard"
> address. Even though as of commit b17d9d1df3c3 ("x86/xen: Add pvh
> specific rsdp address retrieval function") Linux is able to find RSDP,
> for back-compatibility reasons we need to indicate to Xen that we can
> handle this, an we do so by setting XENFEAT_linux_rsdp_unrestricted
> flag in ELF notes.
> 
> (Also take this opportunity and sync features.h header file with Xen)
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>

Reviewed-by: Wei Liu <wei.liu2@...rix.com>