Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753340AbbKPSAF (ORCPT ); Mon, 16 Nov 2015 13:00:05 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39580 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752946AbbKPR77 (ORCPT ); Mon, 16 Nov 2015 12:59:59 -0500 Date: Mon, 16 Nov 2015 19:59:55 +0200 From: "Michael S. Tsirkin" To: =?us-ascii?B?PT9VVEYtOD9xP1JhZGltPTIwS3I9QzQ9OERtPUMzPUExPUM1PTk5Pz0=?= Cc: linux-kernel@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Andy Lutomirski , Xiao Guangrong , Kai Huang , =?us-ascii?B?PT9VVEYtOD9xP01paGFpPTIwRG9uPUM4PTlCdT89?= , kvm@vger.kernel.org Subject: Re: [PATCH] kvm/vmx: EPTP switching test Message-ID: <20151116195453-mutt-send-email-mst@redhat.com> References: <1447598396-6678-1-git-send-email-mst@redhat.com> <20151116175105.GA17144@potion.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151116175105.GA17144@potion.brq.redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2572 Lines: 64 On Mon, Nov 16, 2015 at 06:51:06PM +0100, =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= wrote: > 2015-11-15 18:00+0200, Michael S. Tsirkin: > > This patch adds a new parameter: eptp_switching_test, which enables > > > > testing EPT switching on VMX if supported by hardware. All EPT entries > > are initialized to the same value so this adds no useful functionality > > by itself, but can be used to test VMFUNC performance, and serve as a > > basis for future features based on EPTP switching. > > > > Support for nested virt is not enabled. > > > > This was tested using the following code within guest: > > #define VMX_VMFUNC ".byte 0x0f,0x01,0xd4" > > static void vmfunc(unsigned int nr, unsigned int ept) > > { > > asm volatile(VMX_VMFUNC > > : > > : "a"(nr), "c"(ept) > > : "memory"); > > } > > > > VMFUNC instruction cost was measured at ~122 cycles. > > (Note: recent versions of gnu toolchain support > > the vmfunc instruction - removing the need for writing > > the bytecode manually). > > > > Signed-off-by: Michael S. Tsirkin > > --- > > > > I think I'd like to put this upstream so future eptp switching work can > > be implemented on top. Comments? > > I'd wait for the future. Patch is already on the list so people > interested in benchmarking VMFUNC can quickly compile a kernel and > developers will need to overwrite the code anyway. It'll bitrot though. But I'll let Paolo decide that. > (And I think that eptp switching is expected to be used in conjuction > with #VE, so it'd then make sense to implement a nop for it as well.) No idea how would I even test it, so I'm not interested in #VE at this point. If you are - go ahead and post a patch for that on top though, why not. > > diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h > > @@ -3011,6 +3035,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf) > > SECONDARY_EXEC_PAUSE_LOOP_EXITING | > > SECONDARY_EXEC_RDTSCP | > > SECONDARY_EXEC_ENABLE_INVPCID | > > + SECONDARY_EXEC_ENABLE_VM_FUNCTIONS | > > The VMFUNC vmexit should be handled to prevent guests from triggering a > WARN_ON on the host. (VMFUNC did just #UD before this patch.) Do you mean VMFUNC other than EPTP switch 0? True, thanks! > > After that, it's ok for KVM. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/