From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH 0/7] KVM: x86: Let the guest write to multiple debug registers with one vmexit Date: Sun, 09 Mar 2014 09:11:36 +0100 Message-ID: <531C2238.1060202@web.de> References: <1394192571-11056-1-git-send-email-pbonzini@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="VdgwEv3un76m9KLC7PKQvHFStEOgeObtp" Cc: kvm@vger.kernel.org, alex.williamson@redhat.com, mtosatti@redhat.com, gleb@kernel.org To: Paolo Bonzini , linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1394192571-11056-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --VdgwEv3un76m9KLC7PKQvHFStEOgeObtp Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable On 2014-03-07 12:42, Paolo Bonzini wrote: > Alex Williamson reported that a Windows game does something weird that > makes the guest save and restore debug registers on each context switch= =2E > This cause several hundred thousands vmexits per second, and basically > cuts performance in half when running under KVM. >=20 > However, when not running in guest-debug mode, the guest controls the > debug registers and having to take an exit for each DR access is a wast= e > of time. We just need one vmexit to load any stale values of DR0-DR6, > and then we can let the guest run freely. On the next vmexit (whatever= > the reason) we will read out whatever changes the guest made to the > debug registers. >=20 > Tested with x86/debug.flat on both Intel and AMD, both direct and > nested virtualization. >=20 > Changes from RFC: changed get_dr7 callback to sync_dirty_debug_regs, > new patches 5-7. This looks good now to me from KVM perspective. I was just wondering how the case is handled that the host used debug registers on the thread the runs a VCPU? What if I set a hw breakpoint on its userspace path e.g.? What if I debug the kernel side with kgdb? Jan >=20 > Paolo Bonzini (7): > KVM: vmx: we do rely on loading DR7 on entry > KVM: x86: change vcpu->arch.switch_db_regs to a bit mask > KVM: x86: Allow the guest to run with dirty debug registers > KVM: vmx: Allow the guest to run with dirty debug registers > KVM: nVMX: Allow nested guests to run with dirty debug registers > KVM: svm: set/clear all DR intercepts in one swoop > KVM: svm: Allow the guest to run with dirty debug registers >=20 > arch/x86/include/asm/kvm_host.h | 8 ++++- > arch/x86/kvm/svm.c | 68 ++++++++++++++++++++++++++++-----= -------- > arch/x86/kvm/vmx.c | 43 ++++++++++++++++++++++++-- > arch/x86/kvm/x86.c | 20 +++++++++++- > 4 files changed, 114 insertions(+), 25 deletions(-) >=20 --VdgwEv3un76m9KLC7PKQvHFStEOgeObtp Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlMcIjgACgkQitSsb3rl5xQz7ACfUc6aYzg6QrzHObafVbVEuQRh 8hQAn1ZGSPGASzX4JLfz1ojuYyd4lxLw =Dita -----END PGP SIGNATURE----- --VdgwEv3un76m9KLC7PKQvHFStEOgeObtp--