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From: Will Deacon <will@kernel.org>
To: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Cc: linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
	maz@kernel.org, catalin.marinas@arm.com, james.morse@arm.com,
	julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com,
	jean-philippe@linaro.org, Alexandru.Elisei@arm.com,
	linuxarm@huawei.com
Subject: Re: [PATCH v2 1/3] arch/arm64: Introduce a capability to tell whether 16-bit VMID is available
Date: Wed, 21 Jul 2021 16:23:17 +0100	[thread overview]
Message-ID: <20210721152316.GB11003@willie-the-truck> (raw)
In-Reply-To: <20210616155606.2806-2-shameerali.kolothum.thodi@huawei.com>

On Wed, Jun 16, 2021 at 04:56:04PM +0100, Shameer Kolothum wrote:
> From: Julien Grall <julien.grall@arm.com>
> 
> At the moment, the function kvm_get_vmid_bits() is looking up for the
> sanitized value of ID_AA64MMFR1_EL1 and extract the information
> regarding the number of VMID bits supported.
> 
> This is fine as the function is mainly used during VMID roll-over. New
> use in a follow-up patch will require the function to be called a every
> context switch so we want the function to be more efficient.
> 
> A new capability is introduced to tell whether 16-bit VMID is
> available.

I don't really buy this rationale. The VMID allocator introduced later on
caches this value in the static 'vmid_bits' variable, and that gets used
on vCPU enter via vmid_gen_match() in the kvm_arm_update_vmid() fastpath.

So I would prefer that we just expose an accessor for that than introduce
a static key and new cpufeature just for kvm_get_vttbr().

Will

  reply	other threads:[~2021-07-21 15:23 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-16 15:56 [PATCH v2 0/3] kvm/arm: New VMID allocator based on asid Shameer Kolothum
2021-06-16 15:56 ` [PATCH v2 1/3] arch/arm64: Introduce a capability to tell whether 16-bit VMID is available Shameer Kolothum
2021-07-21 15:23   ` Will Deacon [this message]
2021-07-22  6:24     ` Shameerali Kolothum Thodi
2021-06-16 15:56 ` [PATCH v2 2/3] kvm/arm: Introduce a new vmid allocator for KVM Shameer Kolothum
2021-07-21 16:06   ` Will Deacon
2021-07-22  6:34     ` Shameerali Kolothum Thodi
2021-06-16 15:56 ` [PATCH v2 3/3] kvm/arm: Align the VMID allocation with the arm64 ASID one Shameer Kolothum
2021-07-21 16:31   ` Will Deacon
2021-07-22  6:45     ` Shameerali Kolothum Thodi
2021-07-22  9:11       ` Quentin Perret
2021-07-22 19:33         ` Marco Elver
2021-07-22  9:50       ` Will Deacon
2021-07-22 15:22         ` Vladimir Murzin
2021-07-22 15:38           ` Will Deacon
2021-07-23 15:49             ` Vladimir Murzin
2021-07-13  7:07 ` [PATCH v2 0/3] kvm/arm: New VMID allocator based on asid Shameerali Kolothum Thodi

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