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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.01.2021 20:08, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> 
> 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@xxxxxxxx>
> Reviewed-by: Paul Durrant <paul@xxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> [On Arm only]
> Tested-by: Wei Chen <Wei.Chen@xxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
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