Re: [PATCH v7 03/12] xen/arm: gic-v3: Implement GICv3 suspend/resume functions

[Julien Grall <julien@xxxxxxx>]

Hi,

On 26/12/2025 12:39, Julien Grall wrote:
> Hi Mykola,
>
> On 11/12/2025 18:43, Mykola Kvach wrote:
> > From: Mykola Kvach <mykola_kvach@xxxxxxxx>
> >
> > System suspend may lead to a state where GIC would be powered down.
> > Therefore, Xen should save/restore the context of GIC on suspend/resume.
> >
> > Note that the context consists of states of registers which are
> > controlled by the hypervisor. Other GIC registers which are accessible
> > by guests are saved/restored on context switch.
> >
> > Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
> > ---
> > Changes in V7:
> > - restore LPI regs on resume
> > - add timeout during redist disabling
> > - squash with suspend/resume handling for GICv3 eSPI registers
> > - drop ITS guard paths so suspend/resume always runs; switch missing ctx
> >    allocation to panic
> > - trim TODO comments; narrow redistributor storage to PPI icfgr
> > - keep distributor context allocation even without ITS; adjust resume
> >    to use GENMASK(31, 0) for clearing enables
> > - drop storage of the SGI configuration register, as SGIs are always
> >    edge-triggered
> > ---
> >   xen/arch/arm/gic-v3-lpi.c              |   3 +
> >   xen/arch/arm/gic-v3.c                  | 319 ++++++++++++++++++++++++-
> >   xen/arch/arm/include/asm/gic_v3_defs.h |   1 +
> >   3 files changed, 320 insertions(+), 3 deletions(-)
> >
> > diff --git a/xen/arch/arm/gic-v3-lpi.c b/xen/arch/arm/gic-v3-lpi.c
> > index de5052e5cf..61a6e18303 100644
> > --- a/xen/arch/arm/gic-v3-lpi.c
> > +++ b/xen/arch/arm/gic-v3-lpi.c
> > @@ -391,6 +391,9 @@ static int cpu_callback(struct notifier_block 
> > *nfb, unsigned long action,
> >       switch ( action )
> >       {
> >       case CPU_UP_PREPARE:
> > +        if ( system_state == SYS_STATE_resume )
> > +            break;
> Do we need this check because we don't free the LPI pending table when 
> the CPU is turned off?
> If so, don't we already have a problem for CPU hotplug because the 
> percpu area will be freed but not the pending table?
Looking at [1], we don't seem to support CPU OFF when the GICv3 ITS is 
enabled. So this change could be delayed. But CC Mykyta for awareness.
Cheers,

[1] 
https://lore.kernel.org/48bafdb8e6269a3d958065c6a1062ce2736632a0.1762939773.git.mykyta_poturai@xxxxxxxx
> Cheers,
--
Julien Grall