Re: [PATCH V5 04/22] xen/ioreq: Make x86's IOREQ feature common

From: Jan Beulich <jbeulich@suse.com>
To: Oleksandr Tyshchenko <olekstysh@gmail.com>
Cc: "Oleksandr Tyshchenko" <oleksandr_tyshchenko@epam.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>,
	"Ian Jackson" <iwj@xenproject.org>,
	"Julien Grall" <julien@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>,
	"Paul Durrant" <paul@xen.org>,
	"Jun Nakajima" <jun.nakajima@intel.com>,
	"Kevin Tian" <kevin.tian@intel.com>, "Tim Deegan" <tim@xen.org>,
	"Julien Grall" <julien.grall@arm.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH V5 04/22] xen/ioreq: Make x86's IOREQ feature common
Date: Wed, 27 Jan 2021 17:58:17 +0100	[thread overview]
Message-ID: <01b122dd-37c9-d429-b060-adea9e7cae8b@suse.com> (raw)
In-Reply-To: <1611601709-28361-5-git-send-email-olekstysh@gmail.com>

On 25.01.2021 20:08, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> 
> As a lot of x86 code can be re-used on Arm later on, this patch
> moves previously prepared IOREQ support to the common code
> (the code movement is verbatim copy).
> 
> The "legacy" mechanism of mapping magic pages for the IOREQ servers
> remains x86 specific and not exposed to the common code.
> 
> The common IOREQ feature is supposed to be built with IOREQ_SERVER
> option enabled, which is selected for x86's config HVM for now.
> 
> In order to avoid having a gigantic patch here, the subsequent
> patches will update remaining bits in the common code step by step:
> - Make IOREQ related structs/materials common
> - Drop the "hvm" prefixes and infixes
> - Remove layering violation by moving corresponding fields
>   out of *arch.hvm* or abstracting away accesses to them
> 
> Introduce asm/ioreq.h wrapper to be included by common ioreq.h
> instead of asm/hvm/ioreq.h to avoid HVM-ism in the code common.
> 
> Also include <xen/domain_page.h> which will be needed on Arm
> to avoid touch the common code again when introducing Arm specific bits.
> 
> This support is going to be used on Arm to be able run device
> emulator outside of Xen hypervisor.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> Reviewed-by: Paul Durrant <paul@xen.org>
> CC: Julien Grall <julien.grall@arm.com>
> [On Arm only]
> Tested-by: Wei Chen <Wei.Chen@arm.com>

Acked-by: Jan Beulich <jbeulich@suse.com>
with ...

> --- a/xen/arch/x86/Kconfig
> +++ b/xen/arch/x86/Kconfig
> @@ -92,6 +92,7 @@ config PV_LINEAR_PT
>  
>  config HVM
>  	def_bool !PV_SHIM_EXCLUSIVE
> +	select IOREQ_SERVER
>  	prompt "HVM support"
>  	---help---

... the addition moved below the prompt line (could probably
be taken care of while committing, if no other need for a v6
arises).

(Personally I think this should be

config HVM
	bool "HVM support"
	default !PV_SHIM_EXCLUSIVE
	select IOREQ_SERVER
	---help---

anyway, but that's nothing you need to care about.)

> --- /dev/null
> +++ b/xen/include/asm-x86/ioreq.h
> @@ -0,0 +1,37 @@
> +/*
> + * ioreq.h: Hardware virtual machine assist interface definitions.
> + *
> + * This is a wrapper which purpose is to not include arch HVM specific header
> + * from the common code.
> + *
> + * Copyright (c) 2016 Citrix Systems Inc.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program; If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef __ASM_X86_IOREQ_H__
> +#define __ASM_X86_IOREQ_H__
> +
> +#include <asm/hvm/ioreq.h>
> +
> +#endif /* __ASM_X86_IOREQ_H__ */

Not necessarily for taking care of right away, I think in the
longer run this wants wrapping by #ifdef CONFIG_HVM, such that
in !HVM builds the dependency on the "chained" header goes
away (reducing the amount of rebuilding in incremental builds).

Jan