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Date: Mon, 14 Dec 2015 16:35:32 +0100 From: Roger Pau Monné <roger.pau@...rix.com> To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Boris Ostrovsky <boris.ostrovsky@...cle.com> CC: <3.14+@...r.us.oracle.com>, <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>, <david.vrabel@...rix.com>, <jbeulich@...e.com>, <xen-devel@...ts.xenproject.org>, <#@...r.us.oracle.com> Subject: Re: [Xen-devel] [PATCH] xen/x86/pvh: Use HVM's flush_tlb_others op El 14/12/15 a les 16.27, Konrad Rzeszutek Wilk ha escrit: > On Sat, Dec 12, 2015 at 07:25:55PM -0500, Boris Ostrovsky wrote: >> Using MMUEXT_TLB_FLUSH_MULTI doesn't buy us much since the hypervisor >> will likely perform same IPIs as would have the guest. >> > > But if the VCPU is asleep, doing it via the hypervisor will save us waking > up the guest VCPU, sending an IPI - just to do an TLB flush > of that CPU. Which is pointless as the CPU hadn't been running the > guest in the first place. > >> >> More importantly, using MMUEXT_INVLPG_MULTI may not to invalidate the >> guest's address on remote CPU (when, for example, VCPU from another >> guest >> is running there). > > Right, so the hypervisor won't even send an IPI there. > > But if you do it via the normal guest IPI mechanism (which are opaque > to the hypervisor) you and up scheduling the guest VCPU to do > send an hypervisor callback. And the callback will go the IPI routine > which will do an TLB flush. Not necessary. > > This is all in case of oversubscription of course. In the case where > we are fine on vCPU resources it does not matter. > > Perhaps if we have PV aware TLB flush it could do this differently? Why don't HVM/PVH just uses the HVMOP_flush_tlbs hypercall? Roger. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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