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From: Marc Zyngier <maz@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Fuad Tabba <tabba@google.com>,
	kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	will@kernel.org, qperret@google.com, seanjc@google.com,
	alexandru.elisei@arm.com, catalin.marinas@arm.com,
	philmd@linaro.org, james.morse@arm.com, suzuki.poulose@arm.com,
	oliver.upton@linux.dev, mark.rutland@arm.com, joey.gouly@arm.com,
	rananta@google.com, yuzenghui@huawei.com
Subject: Re: [PATCH v3 05/11] KVM: arm64: Eagerly restore host fpsimd/sve state in pKVM
Date: Mon, 03 Jun 2024 15:31:33 +0100	[thread overview]
Message-ID: <86ikyqkshm.wl-maz@kernel.org> (raw)
In-Reply-To: <382e0746-84a4-4c59-9187-ca9b87f9d265@sirena.org.uk>

On Mon, 03 Jun 2024 15:15:37 +0100,
Mark Brown <broonie@kernel.org> wrote:
> 
> On Mon, Jun 03, 2024 at 02:48:39PM +0100, Marc Zyngier wrote:
> > Mark Brown <broonie@kernel.org> wrote:
> > > On Mon, Jun 03, 2024 at 09:37:16AM +0100, Fuad Tabba wrote:
> 
> > > > Also, one of the concerns in terms of performance is now with
> > > > nested-virt support being added, and the overhead of doing the
> > > > conditional update when we know that it's unlikely that anyone is
> > > > implementing vectors as big as the max.
> 
> > > I guess there's the option of doing a restore of a value fixed during
> > > initialisation instead?
> 
> > And what do we gain from that?
> 
> Reducing the number of places that need updating.

That'd be assuming that the host side value never requires any change
and will be OK with a fixed value. Given that this highly hypothetical
change would be likely to be a hierarchical control much like ZCR_ELx
is today, the fixed value is likely to change on a regular basis.

In any case, this is something we can (re)evaluate when we get to it.
If ever.

	M.

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

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Fuad Tabba <tabba@google.com>,
	kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	will@kernel.org, qperret@google.com, seanjc@google.com,
	alexandru.elisei@arm.com, catalin.marinas@arm.com,
	philmd@linaro.org, james.morse@arm.com, suzuki.poulose@arm.com,
	oliver.upton@linux.dev, mark.rutland@arm.com, joey.gouly@arm.com,
	rananta@google.com, yuzenghui@huawei.com
Subject: Re: [PATCH v3 05/11] KVM: arm64: Eagerly restore host fpsimd/sve state in pKVM
Date: Mon, 03 Jun 2024 15:31:33 +0100	[thread overview]
Message-ID: <86ikyqkshm.wl-maz@kernel.org> (raw)
In-Reply-To: <382e0746-84a4-4c59-9187-ca9b87f9d265@sirena.org.uk>

On Mon, 03 Jun 2024 15:15:37 +0100,
Mark Brown <broonie@kernel.org> wrote:
> 
> On Mon, Jun 03, 2024 at 02:48:39PM +0100, Marc Zyngier wrote:
> > Mark Brown <broonie@kernel.org> wrote:
> > > On Mon, Jun 03, 2024 at 09:37:16AM +0100, Fuad Tabba wrote:
> 
> > > > Also, one of the concerns in terms of performance is now with
> > > > nested-virt support being added, and the overhead of doing the
> > > > conditional update when we know that it's unlikely that anyone is
> > > > implementing vectors as big as the max.
> 
> > > I guess there's the option of doing a restore of a value fixed during
> > > initialisation instead?
> 
> > And what do we gain from that?
> 
> Reducing the number of places that need updating.

That'd be assuming that the host side value never requires any change
and will be OK with a fixed value. Given that this highly hypothetical
change would be likely to be a hierarchical control much like ZCR_ELx
is today, the fixed value is likely to change on a regular basis.

In any case, this is something we can (re)evaluate when we get to it.
If ever.

	M.

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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2024-06-03 14:31 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-05-28 12:59 [PATCH v3 00/11] KVM: arm64: Fix handling of host fpsimd/sve state in protected mode Fuad Tabba
2024-05-28 12:59 ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 01/11] KVM: arm64: Reintroduce __sve_save_state Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-31 12:26   ` Mark Brown
2024-05-31 12:26     ` Mark Brown
2024-06-03  8:28     ` Fuad Tabba
2024-06-03  8:28       ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 02/11] KVM: arm64: Abstract set/clear of CPTR_EL2 bits behind helper Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 03/11] KVM: arm64: Specialize handling of host fpsimd state on trap Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-31 13:35   ` Mark Brown
2024-05-31 13:35     ` Mark Brown
2024-05-28 12:59 ` [PATCH v3 04/11] KVM: arm64: Allocate memory mapped at hyp for host sve state in pKVM Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 05/11] KVM: arm64: Eagerly restore host fpsimd/sve " Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-31 14:09   ` Mark Brown
2024-05-31 14:09     ` Mark Brown
2024-06-03  8:37     ` Fuad Tabba
2024-06-03  8:37       ` Fuad Tabba
2024-06-03 13:27       ` Mark Brown
2024-06-03 13:27         ` Mark Brown
2024-06-03 13:48         ` Marc Zyngier
2024-06-03 13:48           ` Marc Zyngier
2024-06-03 14:15           ` Mark Brown
2024-06-03 14:15             ` Mark Brown
2024-06-03 14:31             ` Marc Zyngier [this message]
2024-06-03 14:31               ` Marc Zyngier
2024-05-28 12:59 ` [PATCH v3 06/11] KVM: arm64: Consolidate initializing the host data's fpsimd_state/sve " Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 07/11] KVM: arm64: Refactor CPACR trap bit setting/clearing to use ELx format Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 08/11] KVM: arm64: Add an isb before restoring guest sve state Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 09/11] KVM: arm64: Do not use sve_cond_update_zcr updating with ZCR_ELx_LEN_MASK Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 10/11] KVM: arm64: Do not perform an isb() if ZCR_EL2 isn't updated Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-28 12:59 ` [PATCH v3 11/11] KVM: arm64: Drop sve_cond_update_zcr_vq_* Fuad Tabba
2024-05-28 12:59   ` Fuad Tabba
2024-05-30 18:22   ` Oliver Upton
2024-05-30 18:22     ` Oliver Upton
2024-05-30 20:14     ` Oliver Upton
2024-05-30 20:14       ` Oliver Upton
2024-05-31  6:40     ` Fuad Tabba
2024-05-31  6:40       ` Fuad Tabba
2024-05-28 13:13 ` [PATCH v3 00/11] KVM: arm64: Fix handling of host fpsimd/sve state in protected mode Fuad Tabba
2024-05-28 13:13   ` Fuad Tabba
2024-05-30 18:29 ` Oliver Upton
2024-05-30 18:29   ` Oliver Upton

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