[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH/RFC] Fix xsave bug on older Xen hypervisors
On Tue, Sep 11, 2012 at 7:37 AM, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote: > On Mon, Sep 10, 2012 at 07:40:47PM -0700, Matt Wilson wrote: >> > Yes, I can verify that a plain upstream kernel has problems in the first >> > place, which is why we are carrying a patch to simply disable xsave all >> > together in the pv guest. >> > EC2 is not carrying a patch to cripple the hypervisor, there was an old >> > xen bug that makes all this fail. The correct fix for that bug is to >> > patch the hypervisor, but they have not done so. Upstream xen has had >> > the fix for quite some time, but that doesn't change the fact that a lot >> > of xen guest usage these days is on EC2. This is no different than >> > putting in a quirk to work around a firmware bug in common use. >> >> I've done some testing and have results that indicate otherwise. The >> out-of-tree xen_write_cr4() patch is not needed as of 2.6.39. I tested >> 3.2.21 on a machine that has XSAVE capabilities: >> >> [ec2-user@ip-10-160-18-80 ~]$ cpuid -1 -i | grep -i xsave/xstor >> XSAVE/XSTOR states = true >> OS-enabled XSAVE/XSTOR = false >> >> on an older hypervisor build: >> >> [ec2-user@ip-10-160-18-80 ~]$ cat /sys/hypervisor/version/major >> 3 >> [ec2-user@ip-10-160-18-80 ~]$ cat /sys/hypervisor/version/minor >> 0 >> >> and it boots without a problem. This patch correctly detects that the >> hypervisor supports XSAVE by testing for OSXSAVE: >> >> commit 947ccf9c3c30307b774af3666ee74fcd9f47f646 >> Author: Shan Haitao <haitao.shan@xxxxxxxxx> >> AuthorDate: Tue Nov 9 11:43:36 2010 -0800 >> Commit: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> >> CommitDate: Wed Apr 6 08:31:13 2011 -0400 >> >> xen: Allow PV-OPS kernel to detect whether XSAVE is supported >> >> Xen fails to mask XSAVE from the cpuid feature, despite not historically >> supporting guest use of XSAVE. However, now that XSAVE support has been >> added to Xen, we need to reliably detect its presence. >> >> The most reliable way to do this is to look at the OSXSAVE feature in >> cpuid which is set iff the OS (Xen, in this case), has set >> CR4.OSXSAVE. >> >> Matt > > Hey Matt, > > Thank you for testing. CC-ing some of the Fedora folks so they are aware that > they > can ditch the: fix_xen_guest_on_old_EC2.patch Ditched. Thanks Matt and Konrad. (BTW, kernel-team@xxxxxxxxxxxxxxxxx is the easiest way to get things to the fedora kernel team.) josh _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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