On Tue, Dec 11, 2018 at 10:38:39AM +0000, Daniel P. Berrangé wrote: > On Mon, Dec 10, 2018 at 06:08:43PM -0200, Eduardo Habkost wrote: > > On Mon, Dec 10, 2018 at 08:42:58PM +0100, Borislav Petkov wrote: > > > On Mon, Dec 10, 2018 at 05:06:00PM -0200, Eduardo Habkost wrote: > > > > I mean documenting it. We already have code that will print > > > > warnings if a feature isn't available. > > > > > > > > See my previous attempt to document the minimum kernel version > > > > at <https://www.mail-archive.com/qemu-devel@xxxxxxxxxx/msg486559.html>. > > > > > > Something like this? > > > > > > I still have no clue how to add RDTSCP on pc-*-4.0 and newer. > > > > qemu.git master have no PC_COMPAT_3_1 and pc-*-4.0 machine-types > > yet. I've sent another reply with additional pointers. > > > > > > > > Thx. > > > > > > --- > > > diff --git a/qemu-doc.texi b/qemu-doc.texi > > > index f7ad1dfe4b69..913b2ef68d54 100644 > > > --- a/qemu-doc.texi > > > +++ b/qemu-doc.texi > > > @@ -37,6 +37,7 @@ > > > * QEMU System emulator for non PC targets:: > > > * QEMU Guest Agent:: > > > * QEMU User space emulator:: > > > +* System requirements:: > > > * Implementation notes:: > > > * Deprecated features:: > > > * Supported build platforms:: > > > @@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes > > > Run the emulation in single step mode. > > > @end table > > > > > > +@node System requirements > > > +@chapter System requirements > > > + > > > +@section KVM kernel module > > > + > > > +On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator > > > +require the host to be running Linux v4.5 or newer. > > > > > > > Sounds good, but it would be nice to document what exactly makes > > Linux 4.5+ necessary. e.g.: > > > > | On x86_64 hosts, it is recommended to run Linux 4.5 or newer on > > | the host when using the KVM accelerator. > > | > > | The Opteron_G2, OpteronG3, Opteron_G4, and Opteron_G5 CPU > > | models require KVM support for RDTSCP, which was added on > > | Linux 4.5. > > > > I'm CCing some people who may help review English grammar and > > style. > > Note that QEMU has a declared supported platform list which is used to > set the minimum software versions required. > > https://qemu.weilnetz.de/doc/qemu-doc.html#Linux-OS > > Based on that policy, the Linux distros we aim to support have the > following kernel versions: > > - Debian Jessie: 4.5 > - Debian Stretch: 4.5 > - RHEL-7: 3.10 > - Ubuntu LTS (Xenial): 4.5 > - OpenSUSE Leap 15: 4.12.14 > > So we can't require Linux 4.5 as a minimum version at this time. I'd like us to take a step back and consider what exactly "support" means here. QEMU will still work on older kernels if we add RDTSCP to the CPU models, but at the same time I would like to document that our strict runnability guarantees may not be kept if running Linux < 4.5. -- Eduardo
