| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Tue, 22 Nov 2022 17:04:33 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: juri.lelli@...hat.com, rafael@...nel.org, catalin.marinas@....com,
linus.walleij@...aro.org, bsegall@...gle.com, guoren@...nel.org,
pavel@....cz, agordeev@...ux.ibm.com, linux-arch@...r.kernel.org,
vincent.guittot@...aro.org, mpe@...erman.id.au,
chenhuacai@...nel.org, christophe.leroy@...roup.eu,
linux-acpi@...r.kernel.org, agross@...nel.org,
geert@...ux-m68k.org, linux-imx@....com, vgupta@...nel.org,
mattst88@...il.com, mturquette@...libre.com, sammy@...my.net,
pmladek@...e.com, linux-pm@...r.kernel.org,
Sascha Hauer <s.hauer@...gutronix.de>,
linux-um@...ts.infradead.org, npiggin@...il.com,
tglx@...utronix.de, linux-omap@...r.kernel.org,
dietmar.eggemann@....com, andreyknvl@...il.com,
gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org, senozhatsky@...omium.org,
svens@...ux.ibm.com, jolsa@...nel.org, tj@...nel.org,
Andrew Morton <akpm@...ux-foundation.org>,
mark.rutland@....com, linux-ia64@...r.kernel.org,
dave.hansen@...ux.intel.com,
virtualization@...ts.linux-foundation.org,
James.Bottomley@...senpartnership.com, jcmvbkbc@...il.com,
thierry.reding@...il.com, kernel@...0n.name, cl@...ux.com,
linux-s390@...r.kernel.org, vschneid@...hat.com,
john.ogness@...utronix.de, ysato@...rs.sourceforge.jp,
linux-sh@...r.kernel.org, festevam@...il.com, deller@....de,
daniel.lezcano@...aro.org, jonathanh@...dia.com, dennis@...nel.org,
lenb@...nel.org, linux-xtensa@...ux-xtensa.org,
kernel@...gutronix.de, gor@...ux.ibm.com,
linux-arm-msm@...r.kernel.org, linux-alpha@...r.kernel.org,
linux-m68k@...ts.linux-m68k.org, loongarch@...ts.linux.dev,
shorne@...il.com, chris@...kel.net, sboyd@...nel.org,
dinguyen@...nel.org, bristot@...hat.com,
alexander.shishkin@...ux.intel.com, fweisbec@...il.com,
lpieralisi@...nel.org, atishp@...shpatra.org,
linux@...musvillemoes.dk, kasan-dev@...glegroups.com,
will@...nel.org, boris.ostrovsky@...cle.com, khilman@...nel.org,
linux-csky@...r.kernel.org, pv-drivers@...are.com,
linux-snps-arc@...ts.infradead.org, mgorman@...e.de,
jacob.jun.pan@...ux.intel.com, Arnd Bergmann <arnd@...db.de>,
ulli.kroll@...glemail.com, linux-clk@...r.kernel.org,
rostedt@...dmis.org, ink@...assic.park.msu.ru, bcain@...cinc.com,
tsbogend@...ha.franken.de, linux-parisc@...r.kernel.org,
ryabinin.a.a@...il.com, sudeep.holla@....com, shawnguo@...nel.org,
davem@...emloft.net, dalias@...c.org, tony@...mide.com,
amakhalov@...are.com, konrad.dybcio@...ainline.org,
bjorn.andersson@...aro.org, glider@...gle.com, hpa@...or.com,
sparclinux@...r.kernel.org, linux-hexagon@...r.kernel.org,
linux-riscv@...ts.infradead.org, vincenzo.frascino@....com,
anton.ivanov@...bridgegreys.com, jonas@...thpole.se,
yury.norov@...il.com, richard@....at, x86@...nel.org,
linux@...linux.org.uk, mingo@...hat.com, aou@...s.berkeley.edu,
hca@...ux.ibm.com, richard.henderson@...aro.org,
stefan.kristiansson@...nalahti.fi, openrisc@...ts.librecores.org,
acme@...nel.org, paul.walmsley@...ive.com,
linux-tegra@...r.kernel.org, namhyung@...nel.org,
andriy.shevchenko@...ux.intel.com, jpoimboe@...nel.org,
dvyukov@...gle.com, jgross@...e.com, monstr@...str.eu,
linux-mips@...r.kernel.org, palmer@...belt.com,
anup@...infault.org, bp@...en8.de, johannes@...solutions.net,
linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 12/44] cpuidle,dt: Push RCU-idle into driver
On Wed, 16 Nov 2022 at 16:29, Peter Zijlstra <peterz@...radead.org> wrote:
>
>
> Sorry; things keep getting in the way of finishing this :/
>
> As such, I need a bit of time to get on-track again..
>
> On Tue, Oct 04, 2022 at 01:03:57PM +0200, Ulf Hansson wrote:
>
> > > --- a/drivers/acpi/processor_idle.c
> > > +++ b/drivers/acpi/processor_idle.c
> > > @@ -1200,6 +1200,8 @@ static int acpi_processor_setup_lpi_stat
> > > state->target_residency = lpi->min_residency;
> > > if (lpi->arch_flags)
> > > state->flags |= CPUIDLE_FLAG_TIMER_STOP;
> > > + if (lpi->entry_method == ACPI_CSTATE_FFH)
> > > + state->flags |= CPUIDLE_FLAG_RCU_IDLE;
> >
> > I assume the state index here will never be 0?
> >
> > If not, it may lead to that acpi_processor_ffh_lpi_enter() may trigger
> > CPU_PM_CPU_IDLE_ENTER_PARAM() to call ct_cpuidle_enter|exit() for an
> > idle-state that doesn't have the CPUIDLE_FLAG_RCU_IDLE bit set.
>
> I'm not quite sure I see how. AFAICT this condition above implies
> acpi_processor_ffh_lpi_enter() gets called, no?
>
> Which in turn is an unconditional __CPU_PM_CPU_IDLE_ENTER() user, so
> even if idx==0, it ends up in ct_idle_{enter,exit}().
Seems like I was overlooking something here, you are right, this
shouldn't really be a problem.
>
> >
> > > state->enter = acpi_idle_lpi_enter;
> > > drv->safe_state_index = i;
> > > }
> > > --- a/drivers/cpuidle/cpuidle-arm.c
> > > +++ b/drivers/cpuidle/cpuidle-arm.c
> > > @@ -53,6 +53,7 @@ static struct cpuidle_driver arm_idle_dr
> > > * handler for idle state index 0.
> > > */
> > > .states[0] = {
> > > + .flags = CPUIDLE_FLAG_RCU_IDLE,
> >
> > Comparing arm64 and arm32 idle-states/idle-drivers, the $subject
> > series ends up setting the CPUIDLE_FLAG_RCU_IDLE for the ARM WFI idle
> > state (state zero), but only for the arm64 and psci cases (mostly
> > arm64). For arm32 we would need to update the ARM_CPUIDLE_WFI_STATE
> > too, as that is what most arm32 idle-drivers are using. My point is,
> > the code becomes a bit inconsistent.
>
> True.
>
> > Perhaps it's easier to avoid setting the CPUIDLE_FLAG_RCU_IDLE bit for
> > all of the ARM WFI idle states, for both arm64 and arm32?
>
> As per the below?
>
> >
> > > .enter = arm_enter_idle_state,
> > > .exit_latency = 1,
> > > .target_residency = 1,
>
> > > --- a/include/linux/cpuidle.h
> > > +++ b/include/linux/cpuidle.h
> > > @@ -282,14 +282,18 @@ extern s64 cpuidle_governor_latency_req(
> > > int __ret = 0; \
> > > \
> > > if (!idx) { \
> > > + ct_idle_enter(); \
> >
> > According to my comment above, we should then drop these calls to
> > ct_idle_enter and ct_idle_exit() here. Right?
>
> Yes, if we ensure idx==0 never has RCU_IDLE set then these must be
> removed.
>
> > > cpu_do_idle(); \
> > > + ct_idle_exit(); \
> > > return idx; \
> > > } \
> > > \
> > > if (!is_retention) \
> > > __ret = cpu_pm_enter(); \
> > > if (!__ret) { \
> > > + ct_idle_enter(); \
> > > __ret = low_level_idle_enter(state); \
> > > + ct_idle_exit(); \
> > > if (!is_retention) \
> > > cpu_pm_exit(); \
> > > } \
> > >
>
> So the basic premise is that everything that needs RCU inside the idle
> callback must set CPUIDLE_FLAG_RCU_IDLE and by doing that promise to
> call ct_idle_{enter,exit}() themselves.
>
> Setting RCU_IDLE is required when there is RCU usage, however even if
> there is no RCU usage, setting RCU_IDLE is fine, as long as
> ct_idle_{enter,exit}() then get called.
Right, I was thinking that it could make sense to shrink the window
for users getting this wrong. In other words, we shouldn't set the
CPUIDLE_FLAG_RCU_IDLE unless we really need to.
And as I said, consistent behaviour is also nice to have.
>
>
> So does the below (delta) look better to you?
Yes, it does!
Although, one minor comment below.
>
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1218,7 +1218,7 @@ static int acpi_processor_setup_lpi_stat
> state->target_residency = lpi->min_residency;
> if (lpi->arch_flags)
> state->flags |= CPUIDLE_FLAG_TIMER_STOP;
> - if (lpi->entry_method == ACPI_CSTATE_FFH)
> + if (i != 0 && lpi->entry_method == ACPI_CSTATE_FFH)
> state->flags |= CPUIDLE_FLAG_RCU_IDLE;
> state->enter = acpi_idle_lpi_enter;
> drv->safe_state_index = i;
> --- a/drivers/cpuidle/cpuidle-arm.c
> +++ b/drivers/cpuidle/cpuidle-arm.c
> @@ -53,7 +53,7 @@ static struct cpuidle_driver arm_idle_dr
> * handler for idle state index 0.
> */
> .states[0] = {
> - .flags = CPUIDLE_FLAG_RCU_IDLE,
> + .flags = 0,
Nitpick: I don't think we need to explicitly clear the flag, as it
should already be zeroed by the compiler from its static declaration.
Right?
> .enter = arm_enter_idle_state,
> .exit_latency = 1,
> .target_residency = 1,
> --- a/drivers/cpuidle/cpuidle-psci.c
> +++ b/drivers/cpuidle/cpuidle-psci.c
> @@ -357,7 +357,7 @@ static int psci_idle_init_cpu(struct dev
> * PSCI idle states relies on architectural WFI to be represented as
> * state index 0.
> */
> - drv->states[0].flags = CPUIDLE_FLAG_RCU_IDLE;
> + drv->states[0].flags = 0;
> drv->states[0].enter = psci_enter_idle_state;
> drv->states[0].exit_latency = 1;
> drv->states[0].target_residency = 1;
> --- a/drivers/cpuidle/cpuidle-qcom-spm.c
> +++ b/drivers/cpuidle/cpuidle-qcom-spm.c
> @@ -72,7 +72,7 @@ static struct cpuidle_driver qcom_spm_id
> .owner = THIS_MODULE,
> .states[0] = {
> .enter = spm_enter_idle_state,
> - .flags = CPUIDLE_FLAG_RCU_IDLE,
> + .flags = 0,
> .exit_latency = 1,
> .target_residency = 1,
> .power_usage = UINT_MAX,
> --- a/drivers/cpuidle/cpuidle-riscv-sbi.c
> +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
> @@ -337,7 +337,7 @@ static int sbi_cpuidle_init_cpu(struct d
> drv->cpumask = (struct cpumask *)cpumask_of(cpu);
>
> /* RISC-V architectural WFI to be represented as state index 0. */
> - drv->states[0].flags = CPUIDLE_FLAG_RCU_IDLE;
> + drv->states[0].flags = 0;
> drv->states[0].enter = sbi_cpuidle_enter_state;
> drv->states[0].exit_latency = 1;
> drv->states[0].target_residency = 1;
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -282,9 +282,7 @@ extern s64 cpuidle_governor_latency_req(
> int __ret = 0; \
> \
> if (!idx) { \
> - ct_idle_enter(); \
> cpu_do_idle(); \
> - ct_idle_exit(); \
> return idx; \
> } \
> \
Kind regards
Uffe
Powered by blists - more mailing lists