----- Original Message ----- > From: "Eduardo Habkost" <ehabk...@redhat.com> > To: "Vincent Bernat" <vinc...@bernat.im> > Cc: "Paolo Bonzini" <pbonz...@redhat.com>, "Richard Henderson" > <r...@twiddle.net>, qemu-devel@nongnu.org > Sent: Monday, January 8, 2018 10:16:23 PM > Subject: Re: [PATCH] target-i386: add pcid to both Sandy Bridge and Ivy Bridge > > On Mon, Jan 08, 2018 at 09:50:52PM +0100, Vincent Bernat wrote: > > PCID has been introduced in Sandy Bridge and, currently, KVM doesn't > > object exposing it to VM as long as it is present on the host. Update > > CPU model for both Sandy Bridge and Ivy Bridge accordingly. > > > > Signed-off-by: Vincent Bernat <vinc...@bernat.im> > > Thanks for your patch. > > We need two things, though: > > First, confirming that all hosts where the SandyBridge and > IvyBridge CPU models are runnable will support exposing PCID to > guests (otherwise updating QEMU can make a runnable VM > configuration suddenly stop being runnable). This can happen if > the host kernel is too old.
I've been reading it's also Westmere. I'll check more carefully tomorrow. The difference between consumer and server SKUs is important too. > One possible way to work around this problem is to declare that > QEMU 2.12 with KVM will require Linux v3.6 and newer (because we > need Linux kernel commit ad756a1603c5 "KVM: VMX: Implement > PCID/INVPCID for guests with EPT"). Note that PCID is still not supported for guests without EPT, so this would break ept=0 with recent "-cpu" models. I'm not sure of a way to fix it; probably it just has to be documented. Paolo
