RE: [PATCH-for-5.1 v2 1/1] accel/xen: Fix xen_enabled() behavior on target-agnostic objects

From: Paul Durrant <xadimgnik@gmail.com>
To: "'Philippe Mathieu-Daudé'" <philmd@redhat.com>, qemu-devel@nongnu.org
Cc: 'Peter Maydell' <peter.maydell@linaro.org>,
	'Stefano Stabellini' <sstabellini@kernel.org>,
	'Paul Durrant' <pdurrant@amazon.com>,
	'Paolo Bonzini' <pbonzini@redhat.com>,
	'Anthony Perard' <anthony.perard@citrix.com>,
	xen-devel@lists.xenproject.org
Subject: RE: [PATCH-for-5.1 v2 1/1] accel/xen: Fix xen_enabled() behavior on target-agnostic objects
Date: Tue, 4 Aug 2020 09:37:16 +0100	[thread overview]
Message-ID: <001301d66a3a$75ac6c90$610545b0$@xen.org> (raw)
In-Reply-To: <56c70b44-2d5f-44fc-5d9a-535c3c5fca71@redhat.com>

> -----Original Message-----
> From: Philippe Mathieu-Daudé <philmd@redhat.com>
> Sent: 04 August 2020 09:35
> To: paul@xen.org; qemu-devel@nongnu.org
> Cc: 'Peter Maydell' <peter.maydell@linaro.org>; 'Anthony Perard' <anthony.perard@citrix.com>; 'Paolo
> Bonzini' <pbonzini@redhat.com>; 'Stefano Stabellini' <sstabellini@kernel.org>; xen-
> devel@lists.xenproject.org; 'Paul Durrant' <pdurrant@amazon.com>
> Subject: Re: [PATCH-for-5.1 v2 1/1] accel/xen: Fix xen_enabled() behavior on target-agnostic objects
> 
> Hi Paul,
> 
> On 8/4/20 9:57 AM, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Philippe Mathieu-Daudé <philmd@redhat.com>
> >> Sent: 04 August 2020 08:50
> >> To: qemu-devel@nongnu.org
> >> Cc: Peter Maydell <peter.maydell@linaro.org>; Anthony Perard <anthony.perard@citrix.com>; Paolo
> >> Bonzini <pbonzini@redhat.com>; Stefano Stabellini <sstabellini@kernel.org>; xen-
> >> devel@lists.xenproject.org; Paul Durrant <paul@xen.org>; Philippe Mathieu-Daudé
> <philmd@redhat.com>;
> >> Paul Durrant <pdurrant@amazon.com>
> >> Subject: [PATCH-for-5.1 v2 1/1] accel/xen: Fix xen_enabled() behavior on target-agnostic objects
> >>
> >> CONFIG_XEN is generated by configure and stored in "config-target.h",
> >> which is (obviously) only include for target-specific objects.
> >> This is a problem for target-agnostic objects as CONFIG_XEN is never
> >> defined and xen_enabled() is always inlined as 'false'.
> >>
> >> Fix by following the KVM schema, defining CONFIG_XEN_IS_POSSIBLE
> >> when we don't know to force the call of the non-inlined function,
> >> returning the xen_allowed boolean.
> >>
> >> Fixes: da278d58a092 ("accel: Move Xen accelerator code under accel/xen/")
> >> Reported-by: Paul Durrant <pdurrant@amazon.com>
> >> Suggested-by: Peter Maydell <peter.maydell@linaro.org>
> >> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> >> ---
> >>  include/sysemu/xen.h   | 18 ++++++++++++++----
> >>  accel/stubs/xen-stub.c |  2 ++
> >>  accel/xen/xen-all.c    |  7 +------
> >>  3 files changed, 17 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/include/sysemu/xen.h b/include/sysemu/xen.h
> >> index 1ca292715e..2c2c429ea8 100644
> >> --- a/include/sysemu/xen.h
> >> +++ b/include/sysemu/xen.h
> >> @@ -8,9 +8,19 @@
> >>  #ifndef SYSEMU_XEN_H
> >>  #define SYSEMU_XEN_H
> >>
> >> -#ifdef CONFIG_XEN
> >> +#ifdef NEED_CPU_H
> >> +# ifdef CONFIG_XEN
> >> +#  define CONFIG_XEN_IS_POSSIBLE
> >> +# endif
> >> +#else
> >> +# define CONFIG_XEN_IS_POSSIBLE
> >> +#endif
> >>
> >> -bool xen_enabled(void);
> >> +#ifdef CONFIG_XEN_IS_POSSIBLE
> >> +
> >> +extern bool xen_allowed;
> >> +
> >> +#define xen_enabled()           (xen_allowed)
> >
> > Can this not move ahead of the #ifdef now (since xen_allowed is present in both xen-stub and xen-
> all)? I think this is what Peter was saying in his option '(2)'.
> 
> I think I respected Peter's option '(2)', following how KVM does, this
> is the case with stub,

Ok, if it follows the KVM pattern then that's fine.

Reviewed-by: Paul Durrant <paul@xen.org>