From: David Gibson <david@gibson.dropbear.id.au>
To: Thomas Huth <thuth@redhat.com>
Cc: paulus@samba.org, michael@ellerman.id.au,
benh@kernel.crashing.org, sjitindarsingh@gmail.com,
lvivier@redhat.com, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 01/11] powerpc/kvm: Reserve capabilities and ioctls for HPT resizing
Date: Mon, 19 Dec 2016 17:36:14 +1100 [thread overview]
Message-ID: <20161219063614.GA23176@umbus.fritz.box> (raw)
In-Reply-To: <25bcced1-4903-2cf7-6a56-14c3ced5cd28@redhat.com>
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On Fri, Dec 16, 2016 at 10:25:55AM +0100, Thomas Huth wrote:
> On 15.12.2016 06:53, David Gibson wrote:
> > This adds a new powerpc-specific KVM_CAP_SPAPR_RESIZE_HPT capability to
> > advertise whether KVM is capable of handling the PAPR extensions for
> > resizing the hashed page table during guest runtime.
> >
> > At present, HPT resizing is possible with KVM PR without kernel
> > modification, since the HPT is managed within qemu. It's not possible yet
> > with KVM HV, because the HPT is managed by KVM. At present, qemu has to
> > use other capabilities which (by accident) reveal whether PR or HV is in
> > use to know if it can advertise HPT resizing capability to the guest.
> >
> > To avoid ambiguity with existing kernels, the encoding is a bit odd.
> > 0 means "unknown" since that's what previous kernels will return
> > 1 means "HPT resize possible if available if and only if the HPT is allocated in
> > userspace, rather than in the kernel". Userspace can check
> > KVM_CAP_PPC_ALLOC_HTAB to determine if that's the case. In practice
> > this will give the same results as userspace's fallback check.
> > 2 will mean "HPT resize available and implemented via ioctl()s
> > KVM_PPC_RESIZE_HPT_PREPARE and KVM_PPC_RESIZE_HPT_COMMIT"
>
> This encoding IMHO clearly needs some proper documentation in
> Documentation/virtual/kvm/api.txt ... and maybe also some dedicated
> #defines in an uapi header file.
Ah, yeah. Actually I'm talking to paulus again to see if we can come
up with a way to encode the necessary facts without something as weird
as this one.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2016-12-19 8:10 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-15 5:53 [PATCH 00/11] KVM implementation of PAPR HPT resizing extension David Gibson
2016-12-15 5:53 ` [PATCH 01/11] powerpc/kvm: Reserve capabilities and ioctls for HPT resizing David Gibson
2016-12-16 9:25 ` Thomas Huth
2016-12-19 6:36 ` David Gibson [this message]
2016-12-16 13:15 ` Thomas Huth
2016-12-19 6:37 ` David Gibson
2016-12-15 5:53 ` [PATCH 02/11] powerpc/kvm: Rename kvm_alloc_hpt() for clarity David Gibson
2016-12-16 9:03 ` Thomas Huth
2016-12-15 5:53 ` [PATCH 03/11] powerpc/kvm: Gather HPT related variables into sub-structure David Gibson
2016-12-16 9:24 ` Thomas Huth
2016-12-19 0:03 ` David Gibson
2016-12-15 5:53 ` [PATCH 04/11] powerpc/kvm: Don't store values derivable from HPT order David Gibson
2016-12-16 10:39 ` Thomas Huth
2016-12-19 0:04 ` David Gibson
2016-12-15 5:53 ` [PATCH 05/11] powerpc/kvm: Split HPT allocation from activation David Gibson
2016-12-16 11:57 ` Thomas Huth
2016-12-19 0:24 ` David Gibson
2016-12-15 5:53 ` [PATCH 06/11] powerpc/kvm: Allow KVM_PPC_ALLOCATE_HTAB ioctl() to change HPT size David Gibson
2016-12-16 12:44 ` Thomas Huth
2016-12-19 0:48 ` David Gibson
2016-12-19 7:49 ` Thomas Huth
2016-12-19 23:16 ` David Gibson
2016-12-15 5:54 ` [PATCH 07/11] powerpc/kvm: Create kvmppc_unmap_hpte_helper() David Gibson
2016-12-16 12:48 ` Thomas Huth
2016-12-15 5:54 ` [PATCH 08/11] powerpc/kvm: KVM-HV HPT resizing stub implementation David Gibson
2016-12-16 15:35 ` Thomas Huth
2016-12-15 5:54 ` [PATCH 09/11] powerpc/kvm: Outline of KVM-HV HPT resizing implementation David Gibson
2016-12-15 5:54 ` [PATCH 10/11] powerpc/kvm: " David Gibson
2016-12-15 5:54 ` [PATCH 11/11] powerpc/kvm: Advertise availablity of HPT resizing on KVM HV David Gibson
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