linux-kernel - Re: [PATCH 01/11] powerpc/kvm: Reserve capabilities and ioctls for HPT resizing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20161219063614.GA23176@umbus.fritz.box>
Date:   Mon, 19 Dec 2016 17:36:14 +1100
From:   David Gibson <david@...son.dropbear.id.au>
To:     Thomas Huth <thuth@...hat.com>
Cc:     paulus@...ba.org, michael@...erman.id.au, benh@...nel.crashing.org,
        sjitindarsingh@...il.com, lvivier@...hat.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 01/11] powerpc/kvm: Reserve capabilities and ioctls for
 HPT resizing

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

Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)