> -----Original Message----- > From: Will Deacon [mailto:will@xxxxxxxxxx] > Sent: 21 July 2021 16:23 > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx> > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; maz@xxxxxxxxxx; catalin.marinas@xxxxxxx; > james.morse@xxxxxxx; julien.thierry.kdev@xxxxxxxxx; > suzuki.poulose@xxxxxxx; jean-philippe@xxxxxxxxxx; > Alexandru.Elisei@xxxxxxx; Linuxarm <linuxarm@xxxxxxxxxx> > Subject: Re: [PATCH v2 1/3] arch/arm64: Introduce a capability to tell whether > 16-bit VMID is available > > On Wed, Jun 16, 2021 at 04:56:04PM +0100, Shameer Kolothum wrote: > > From: Julien Grall <julien.grall@xxxxxxx> > > > > 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(). Ok. Will change it to an accessor. Thanks, Shameer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
