linux-kernel - Re: [PATCH] irqchip/gic-v3-its: Don't need VSYNC if VMAPP with {V, Alloc}=={0, x}

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Message-ID: <86il0zubh1.wl-maz@kernel.org>
Date: Tue, 02 Apr 2024 14:43:06 +0100
From: Marc Zyngier <maz@...nel.org>
To: Tangnianyao <tangnianyao@...wei.com>
Cc: <tglx@...utronix.de>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>,
	<guoyang2@...wei.com>,
	<wangwudi@...ilicon.com>
Subject: Re: [PATCH] irqchip/gic-v3-its: Don't need VSYNC if VMAPP with {V, Alloc}=={0, x}

On Tue, 02 Apr 2024 14:32:40 +0100,
Tangnianyao <tangnianyao@...wei.com> wrote:
> 
> 
> 
> On 4/2/2024 20:35, Marc Zyngier wrote:
> > On Tue, 02 Apr 2024 12:41:47 +0100,
> > t00849498 <tangnianyao@...wei.com> wrote:
> >> From GIC spec, a VMAPP with {V, Alloc}=={0, x} is self-synchronizing,
> > It'd be nice to quote the part of the spec (5.3.19).
> yes, that's quote from GIC spec.
> >> This means the ITS command queue does not show the command as
> >> consumed until all of its effects are completed. A VSYNC with unmapped
> >> vpeid is not needed.
> >>
> >> Signed-off-by: t00849498 <tangnianyao@...wei.com>
> > Previous contributions with the same email address had the name
> > "Nianyao Tang" associated with it. Was it wrong in the past? Or is the
> > above wrong?
> Sorry, the above name is wrong, should be "Nianyao Tang".
> >
> >> ---
> >>  drivers/irqchip/irq-gic-v3-its.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> >> index fca888b36680..a0ca5dcbb245 100644
> >> --- a/drivers/irqchip/irq-gic-v3-its.c
> >> +++ b/drivers/irqchip/irq-gic-v3-its.c
> >> @@ -789,6 +789,7 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
> >>  	unsigned long vpt_addr, vconf_addr;
> >>  	u64 target;
> >>  	bool alloc;
> >> +	bool unmap_v4_1 = !desc->its_vmapp_cmd.valid && is_v4_1(its);
> >>
> >>  	its_encode_cmd(cmd, GITS_CMD_VMAPP);
> >>  	its_encode_vpeid(cmd, desc->its_vmapp_cmd.vpe->vpe_id);
> >> @@ -832,6 +833,9 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
> >>  out:
> >>  	its_fixup_cmd(cmd);
> >>  
> >> +	if (unmap_v4_1)
> >> +		return NULL;
> >> +
> >>  	return valid_vpe(its, desc->its_vmapp_cmd.vpe);
> >>  }
> >>  
> > This is a bit ugly. We already have a whole block dedicated to
> > handling VMAPP with V=0 and GICv4.1, and it'd be more readable to keep
> > all that code together. Something like the untested patch below.
> 
> Thank you for quick fix, it would be great to remove this VSYNC. ITS handling VSYNC unmap
> vpeid may waste some time, trigger exception and needed to be
> handled.

Do you actually see an exception being delivered from this?

In any case, feel free to respin the patch after having tested this
diff, with the commit message fixed and a Fixes: tag attached to it.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.