Re: [PATCH 02/10] accel/tcg: move cpu_reloading_memory_map into cpu-exec-softmmu

[Claudio Fontana <cfontana@suse.de>]

How is this conditional on CONFIG_TCG? To me it looks like this breaks !CONFIG_TCG.
Careful, the meson.build in accel/tcg/meson.build is always recursed.

This code was in tcg_ss before, why not simply add it to tcg_ss and then to specific_ss along with the other tcg pieces?

Ciao,

C


On 3/20/23 11:10, Alex Bennée wrote:
> This doesn't save much as cpu-exec-common still needs to be built
> per-target for its knowledge of CPUState but this helps with keeping
> things organised.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  accel/tcg/cpu-exec-common.c  | 30 ----------------------
>  accel/tcg/cpu-exec-softmmu.c | 50 ++++++++++++++++++++++++++++++++++++
>  accel/tcg/meson.build        | 10 ++++++++
>  3 files changed, 60 insertions(+), 30 deletions(-)
>  create mode 100644 accel/tcg/cpu-exec-softmmu.c
> 
> diff --git a/accel/tcg/cpu-exec-common.c b/accel/tcg/cpu-exec-common.c
> index e7962c9348..c6b0ad303e 100644
> --- a/accel/tcg/cpu-exec-common.c
> +++ b/accel/tcg/cpu-exec-common.c
> @@ -32,36 +32,6 @@ void cpu_loop_exit_noexc(CPUState *cpu)
>      cpu_loop_exit(cpu);
>  }
>  
> -#if defined(CONFIG_SOFTMMU)
> -void cpu_reloading_memory_map(void)
> -{
> -    if (qemu_in_vcpu_thread() && current_cpu->running) {
> -        /* The guest can in theory prolong the RCU critical section as long
> -         * as it feels like. The major problem with this is that because it
> -         * can do multiple reconfigurations of the memory map within the
> -         * critical section, we could potentially accumulate an unbounded
> -         * collection of memory data structures awaiting reclamation.
> -         *
> -         * Because the only thing we're currently protecting with RCU is the
> -         * memory data structures, it's sufficient to break the critical section
> -         * in this callback, which we know will get called every time the
> -         * memory map is rearranged.
> -         *
> -         * (If we add anything else in the system that uses RCU to protect
> -         * its data structures, we will need to implement some other mechanism
> -         * to force TCG CPUs to exit the critical section, at which point this
> -         * part of this callback might become unnecessary.)
> -         *
> -         * This pair matches cpu_exec's rcu_read_lock()/rcu_read_unlock(), which
> -         * only protects cpu->as->dispatch. Since we know our caller is about
> -         * to reload it, it's safe to split the critical section.
> -         */
> -        rcu_read_unlock();
> -        rcu_read_lock();
> -    }
> -}
> -#endif
> -
>  void cpu_loop_exit(CPUState *cpu)
>  {
>      /* Undo the setting in cpu_tb_exec.  */
> diff --git a/accel/tcg/cpu-exec-softmmu.c b/accel/tcg/cpu-exec-softmmu.c
> new file mode 100644
> index 0000000000..2318dd8c7d
> --- /dev/null
> +++ b/accel/tcg/cpu-exec-softmmu.c
> @@ -0,0 +1,50 @@
> +/*
> + *  Emulator main CPU execution loop, softmmu bits
> + *
> + *  Copyright (c) 2003-2005 Fabrice Bellard
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/core/cpu.h"
> +#include "sysemu/cpus.h"
> +
> +void cpu_reloading_memory_map(void)
> +{
> +    if (qemu_in_vcpu_thread() && current_cpu->running) {
> +        /* The guest can in theory prolong the RCU critical section as long
> +         * as it feels like. The major problem with this is that because it
> +         * can do multiple reconfigurations of the memory map within the
> +         * critical section, we could potentially accumulate an unbounded
> +         * collection of memory data structures awaiting reclamation.
> +         *
> +         * Because the only thing we're currently protecting with RCU is the
> +         * memory data structures, it's sufficient to break the critical section
> +         * in this callback, which we know will get called every time the
> +         * memory map is rearranged.
> +         *
> +         * (If we add anything else in the system that uses RCU to protect
> +         * its data structures, we will need to implement some other mechanism
> +         * to force TCG CPUs to exit the critical section, at which point this
> +         * part of this callback might become unnecessary.)
> +         *
> +         * This pair matches cpu_exec's rcu_read_lock()/rcu_read_unlock(), which
> +         * only protects cpu->as->dispatch. Since we know our caller is about
> +         * to reload it, it's safe to split the critical section.
> +         */
> +        rcu_read_unlock();
> +        rcu_read_lock();
> +    }
> +}
> diff --git a/accel/tcg/meson.build b/accel/tcg/meson.build
> index aeb20a6ef0..bdc086b90d 100644
> --- a/accel/tcg/meson.build
> +++ b/accel/tcg/meson.build
> @@ -1,3 +1,9 @@
> +#
> +# Currently most things here end up in specific_ss eventually because
> +# they need knowledge of CPUState. Stuff that that doesn't can live in
> +# common user, softmmu or overall code
> +#
> +
>  tcg_ss = ss.source_set()
>  tcg_ss.add(files(
>    'tcg-all.c',
> @@ -9,6 +15,7 @@ tcg_ss.add(files(
>    'translate-all.c',
>    'translator.c',
>  ))
> +
>  tcg_ss.add(when: 'CONFIG_USER_ONLY', if_true: files('user-exec.c'))
>  tcg_ss.add(when: 'CONFIG_SOFTMMU', if_false: files('user-exec-stub.c'))
>  tcg_ss.add(when: 'CONFIG_PLUGIN', if_true: [files('plugin-gen.c')])
> @@ -27,3 +34,6 @@ tcg_module_ss.add(when: ['CONFIG_SOFTMMU', 'CONFIG_TCG'], if_true: files(
>    'tcg-accel-ops-icount.c',
>    'tcg-accel-ops-rr.c',
>  ))
> +
> +# Common softmmu code
> +softmmu_ss.add(files('cpu-exec-softmmu.c'))